Author: lbrown (page 1 of 2)

The Aerodynamics of Flying a Frisbee

Introduction

Are you good at tossing a Frisbee? Have you ever wondered how a Frisbee is able to fly through the air so well? If you can throw a perfect, arcing curve, right on target, you have already trained your arm on the aerodynamics of Frisbee flight! In this science activity, you will investigate how the angle at which you throw the Frisbee affects its flight’s direction and distance. Next time you are out tossing a Frisbee, this little lesson in aerodynamics may help make your throws be even better!

Time: 20-30 minutes

Key concepts: aerodynamics, forces, physics, lift, drag

 

 

 

Materials

  • A Frisbee
  • Long string or hose
  • Tape measure
  • Large open area to toss a Frisbee in
  • Optional: A helper
  • Optional: A piece of paper and a pen or pencil

 

 

Prep Work

  1. Use the long string or hose to make a long, straight line in front of you, at least 25 feet long. You will be throwing the Frisbee so that it is directed down this centerline.
  2. Practice throwing the Frisbee down the straight line a few times so you get used to tossing it. If you have not thrown a Frisbee much before, you may want to try practicing it for a little while. Tip: A good way to throw a Frisbee is by standing sideways with the Frisbee held in front of you (near the shoulder you are looking away from), then bringing the Frisbee horizontally across you as you throw it.
  3. If there is wind during any of your Frisbee throws, note the wind speed and direction.

 

Procedure

  1. Throw the Frisbee as flat and horizontal as you can, aiming it down the centerline you made. You can have a helper watch to confirm the angle at which you throw the Frisbee. Question: How far did the Frisbee travel? How far did it travel away from the centerline, and in what direction?
  2. If you have a piece of paper and a pencil or pen, you can record this data and all following flight data.
  3. Throw the Frisbee as flat and horizontal as you can at least four more times. Each time throw the Frisbee with similar arm motion and speed, use a similar spin, and have the same release point. How far did the Frisbee travel each time? How far did it travel away from the centerline, and in what direction?
  4. Throw the Frisbee tilted up, aiming for between 1 o’clock and 2 o’clock (about a 45-degree angle up from the ground). Throw it this way at least five times. Other than changing the launch angle, try to keep all other aspects of the Frisbee flights the same. How far did the Frisbee travel each time when thrown at an upward angle? How far did it travel away from the centerline, and in what direction?
  5. Throw the Frisbee tilted down, aiming for between 4 o’clock and 5 o’clock (about a 45-degree angle down towards the ground), at least five times. Again try to keep all other aspects of the Frisbee flights the same. How far did the Frisbee travel each time when thrown at a downward angle? How far did it travel away from the centerline, and in what direction?
  6. Did you see a consistent relationship between launch angle and flight direction? Question: Is there a relationship between launch angle and distance? Why do you think you saw the relationships that you did?

 

What Happened?

To fly well, the Frisbee needs enough lift — which is the force that allows a Frisbee to stay in the air, and opposes the downward force of gravity — and not too much drag — which is the backward force on a Frisbee, going against its movement through the air. When a Frisbee is thrown tilted downward, it hits the ground sooner, so it does not have as much time to travel before it lands. As a result, it does not go as far. A Frisbee will go farther if you throw it horizontally or at an upward angle, since it will have a good amount of lift and will not crash into the ground right away. However, you may have noticed that if you throw a Frisbee up at too steep of an angle, it will probably stall out near the end of its flight, causing it to land gently and/or off to the side. When something flying through the air stalls, there is too much drag and not enough lift. Overall, the horizontal launches probably resulted in the overall “best” Frisbee throws in terms of distance and straightness.

 

Digging Deeper

Two key forces that act on a Frisbee during its flight are lift and drag. Lift is the force that allows the Frisbee to stay in the air, and it opposes the force of gravity on the mass of the Frisbee in flight. The Frisbee itself creates this lift force as it flies through the air. The Frisbee pushes air out of the way as it moves, and causes a slight downward motion of the air. The air pushes back up on the Frisbee, creating the lift force. Drag is a backward force on the Frisbee, and it goes against the Frisbee’s movement through the air, slowing it down. The force of drag acts perpendicular to the force of lift. The Frisbee’s shape, velocity, and angle at which it moves relative to the still air (called the “angle of attack”) all affect both the lift and drag.

As a side note, you have probably noticed that a Frisbee does not travel far if it is thrown without spin. Spinning the Frisbee helps it fly by supplying angular momentum, which helps keep the Frisbee stable while it is rotating. The faster it spins, the more stable it should be.

 

For Further Exploration

  • In this activity, you investigated how the launch angle of the Frisbee affects its flight’s distance and direction, but you only tested a few angles. You can try this activity again but test even more angles, such as angles in between the ones you tried in this activity. You can videotape your throws and then watch the video to analyze and confirm the angles at which you threw the Frisbee. How well does the Frisbee fly using other launch angles? Is there an angle that consistently correlates with the “best” flight in terms of distance and stability?
  • In this activity there was not a focus on the effects of wind on a Frisbee’s trajectory, but wind can definitely be a factor. How will the flight of the Frisbee be affected by throwing the Frisbee into the wind? What about across the wind or with the wind? How does the launch angle change the flight in each of these conditions?
  • You could compare the flight of a Frisbee to the flight of an Aerobie (open ring flying disk). What differences do you notice? Can you explain them in terms of aerodynamic forces?
  • The National Aeronautics and Space Administration (NASA) website has a great section on Aerodynamics. See The Beginner’s Guide to Aerodynamics.

 

Science Careers

 

Credit

Teisha Rowland, PhD, Science Buddies

Ben Finio, PhD, Science Buddies

Program Your Own COVID-19 Simulator with Scratch

Introduction

Do you keep hearing phrases like “social distancing” and “flatten the curve” in the news? What do they mean? Why are they important? In this activity, you will use the kid-friendly programming language Scratch to write a simulation that uses bouncing dots to represent healthy and sick people. The simulation will show how we can take measures to slow the spread of a transmissible disease like COVID-19.

Time: 1-2 hours

Key Concepts: Programming, disease transmission, social distancing
Materials
All you need is your MacBook with access to Scratch

 

Prep Work

1. Create an account at scratch.mit.edu.

2. Optionally, if you have never used Scratch before, you can follow some of their tutorials.

 

Procedure

  • Watch this video for an overview of how to create a basic COVID-19 simulator in Scratch:

 

  • Now, you can either start with a blank project of your own, or you can “remix” this Science Buddies Scratch project. You can also run the simulation here:

  • Once you have a working simulation, explore the effects of social distancing.
  • What happens if you increase the number of “people” in the simulation? To do this in the Science Buddies project, increase the “num_clones” variable.
  • What happens if the people in the simulation practice social distancing? To do this in the Science Buddies project, increase the second number in the “pick random 1 to 1” block. Question: Why is social distancing important to help slow the spread of infectious diseases like COVID-19?
  • See the Further Exploration section suggestions about more things you could add to your program.

What Happened?

In your Scratch simulation, people are represented by colored dots that bounce around the screen. Green dots are healthy and red dots are sick. The virus is passed between dots that touch each other, representing close personal contact. When all the dots are moving around, they bump into each other very frequently, allowing the virus to spread rapidly. When people “stay home” (some of the dots hold still), it takes much longer for the virus to spread.

Digging Deeper

Infectious diseases like COVID-19 are spread primarily through close person-to-person contact, including through droplets people emit when they cough or sneeze. This means that you are at the highest risk for catching the virus through daily contact with other people, like shaking hands with a sick person or sitting next to a coughing person on the bus. Once you are infected with the virus, you, in turn, can spread it to others. This is why social distancing—avoiding large gatherings, and staying at least 6 feet away from others in public places—is important to help slow the spread of the virus. Slowing the spread of the virus means that, at any given time, fewer people overall will have it. This, along with other preventative measures like frequent hand washing, helps “flatten the curve,” and keep the total number of sick people below our healthcare system’s capacity. You can visualize this effect by implementing social distancing in your Scratch simulation, which slows the rate at which the virus spreads.

 

Further Exploration

  • Add a timer and make your program stop when every person is infected.
  • Add counters for the number of healthy and sick individuals in your simulation.
  • Add recovery to your simulation, so individuals eventually get better (or die) after they become infected.
  • Make the dots bounce off of each other instead of passing through each other.
  • Add an animated graph showing the number of healthy/infected (and recovered/dead) individuals over time.
  • Include a “super spreader” (a dot that moves faster than all the other ones).

 

Credits

Ben Finio, PhD, Science Buddies

Why Soda Fizzes — Boyle’s Law Demonstration

Introduction

You have probably cracked open a soda before to see the liquid fizz right up out of the bottle, creating a huge mess. Why does that happen? It has to do with the carbon dioxide gas that is added to the liquid to make it fizzy. Opening the bottle releases the built-up pressure by the gas inside, causing the gas-liquid mixture to rush out the bottle. In this activity, you will demonstrate with the help of air- and water-filled balloons how a gas changes volume depending on its pressure.

Time: 30-45 minutes

Key Concepts: Boyle’s Law, gas, volume, pressure
Materials
  • Small balloons such as water balloons (2, additional 2 optional)
  • 60 mL syringe (without needle) Note: the syringe needs to be airtight.
  • Scissor
  • Tap water
  • Food color (optional)

Prep Work
  1. Fill the syringe with water. Then fill one balloon with some of the water and tie its opening with a knot. Cut the neck off right above the knot. The balloon should still be small enough to fit into the syringe.
  2. Use the syringe to fill the second balloon with a little bit of air. It should be the same size as the water-filled balloon. Again, tie the balloon opening with a knot and cut off the remaining parts right above the knot.

 

Procedure

  1. Put the air-filled balloon inside the syringe at the very end. Insert the plunger into the syringe and try to push the balloon into the tip of the syringe. Question: How hard is it to push the plunger in? What happens to the air inside the syringe?
  2. Pull the plunger back again and move the balloon into the middle of the syringe. Then close the front opening (the tip) of the syringe with one finger and push the plunger into the syringe again. Question: What do you notice? How does the balloon look or change when you push the plunger in?
  3. Release your finger from the tip of the syringe. Place the balloon into the tip of the syringe and push the plunger into the syringe until it touches the balloon. Then pull the plunger all the way back while again closing the tip of the syringe with your finger. Question: Does the balloon shape change? How? Can you explain why?
  4. Replace the air-filled balloon inside the syringe with the water-filled balloon. Then place the plunger into the syringe. Close the tip of the syringe with your finger and push the plunger into the syringe as far as you can. Question: How does the balloon change this time?
  5. Release your finger from the tip of the syringe and push the plunger all the way into the syringe until it touches the balloon at the tip of the syringe. Then close the tip of the syringe again with your finger and try to pull the plunger back as far as you can. Question: What happens to the water-filled balloon? Does it behave differently than the air-filled balloon? If yes, how and why?

 

What Happened?

Did you see the air inside the air-filled balloon contract and expand? You should have! Without closing the tip of the syringe with your finger, you can easily push on the plunger. The air can escape through the opening at the tip of the syringe. However, when you close the syringe with your finger, the air can’t escape anymore. If you press on the plunger, you increase the pressure of the air and thus the air in the balloon contracts or decreases its volume. You should have seen the air-filled balloon shrivel up and get smaller in size. The opposite happens when you pull the plunger back while closing the opening of the syringe. This time, you decrease the pressure of the air inside the syringe and its volume increases. As a result, the air-filled balloon expands and grows in size. A perfect demonstration of Boyle’s law!

The results look different with the water-filled balloon. Although you are compressing the air inside the syringe when pressing on the plunger, the water inside the balloon does not get compressed. The balloon stays the same size. The water balloon also keeps its shape when pulling out the plunger while closing the tip of the syringe. In contrast to gases, liquids are not compressible as their particles are already very close together. Boyle’s law is only valid for gases.

When you filled the syringe with water as well, you still should have seen the air-filled balloon shrinking while pushing the plunger into the syringe. The air-filled balloon also should have expanded when pulling the plunger out while the tip of the syringe was closed. You might have noticed, though, that you were not able to push and pull the plunger in and out as far as you could with the air-filled syringe. This is again due to the fact that liquids cannot be compressed like gases. You should have observed that also when trying to push the plunger in or pulling it back in the water-filled syringe with the water-filled balloon. It was impossible to move the plunger in and out!

 

Digging Deeper

The difference between solids, liquids, and gases is how the particles (molecules or atoms) they are made of behave. Particles in solids are usually tightly packed in a regular pattern. Although the particles in a liquid are also close together, they are able to move freely with respect to one another. Gas particles, however, are widely spread out and occupy lots of space. They continue to spread to any space that is available. This means that in contrast to liquids and solids, the volume of a gas is not fixed. Robert Boyle, a chemist and physicist form the 17th century, discovered that the volume of gas, meaning how much space it occupies, is related to its pressure, and vice versa. He found that if you pressurize a gas at a constant temperature, its volume contracts. If you decrease its pressure, its volume increases.

You can observe a real-life application of Boyle’s Law when you fill your bike tires with air. When you pump air into a tire, the gas molecules inside the tire get compressed and packed closer together. This increases the pressure of the gas, and it starts to push against the walls of the tire. You can feel how the tire becomes pressurized and tighter. Another example is a soda bottle. To get carbon dioxide gas into the liquid, the whole bottle is usually pressurized with gas. As long as the bottle is closed, it is very hard to squeeze, as the gas is confined to a small space and pushes against the bottle’s walls. However, when you remove the cap, the available volume increases, and the gas escapes. At the same time, its pressure decreases. If the gas/liquid mixture was shaken too much, the liquid would shoot out of the bottle together with the gas—and there you have the mess!

One rather important demonstration of Boyle’s law is our own breathing. Inhaling and exhaling basically means increasing or decreasing the volume of our chest cavity. This creates low pressure or high pressure in our lungs, resulting in air either getting sucked into our lungs or leaving our lungs.

 

For Further Exploration

Use the same setup as in your experiment, but this time, add water to your syringe in addition to the air-filled and water-filled balloons. You can add a drop of food coloring to make the water more visible. Then close the tip of the syringe and try to press the plunger into the syringe and pull it out again. What happens this time? How does the water inside the syringe make a difference?

Credits
Svenja Lohner, PhD, Science Buddies

When Science is Sweet: Growing Rock Candy Crystals

Introduction

Have you ever looked at rock candy and wondered how it’s made? Rock candy is actually a collection of large sugar crystals that are “grown” from a sugar-water solution. Sugar, like many other materials, can come in many different physical states. As a solid it can either be amorphous, without shape, like when it forms cotton candy, or crystalline, with a highly ordered structure and shape, like when it forms rock candy crystals.

Crystals form when the smallest particles of a substance, the molecules, arrange themselves in an orderly and repetitive pattern. Molecules are too small for us to see moving around and arranging themselves, but you can get a rough idea of what this would look like by taking a small shallow tray and filling it with marbles, ball bearings, or other spheres. As you add more spheres, the bottom of the tray becomes covered, then the spheres must form layers on top of one another, and a structure or pattern emerges.

So how do the molecules of a substance get together to form a crystal? First there have to be enough molecules in one area that they have a high chance of bumping into one another. This happens when a solution, which is made up of a liquid and the compound that will be crystallized, is saturated. In the rock candy, the liquid is water and the compound is sugar. A solution is saturated when the liquid holds as much of the compound dissolved in it as possible. For example, when making rock candy, you dissolve as much sugar as possible in water to make a saturated solution. If you add more compound than can dissolve in the liquid, the undissolved bits remain as solids in the liquid. In a saturated solution, the molecules bump into one another frequently because there are so many of them. Occasionally when they bump into each other, the molecules end up sticking together; this is the beginning of the crystallization process and is called nucleation. Once several molecules are already stuck together, they actively attract other molecules to join them. This slow process is how the crystal “grows.”

Time: Average (6-10 days)

Key Concepts: crystalline solid, seed crystals

 

 

Figure 1. This diagram illustrates the large number of molecules in a saturated solution. With so many molecules in the liquid, there is a high chance of them bumping into one another and creating a nucleation event.

In this science project, you will make a saturated solution of sugar and water in order to grow your own rock candy sugar crystals. You will compare the rate of growth between rock candy that is left to nucleate on its own in the solution, and rock candy that starts off with some assistance. To assist this rock candy, you will jump-start the nucleation process by adding sugar crystals, called seed crystals, to the string first.

Terms and Concepts

Here are some terms you should know, and questions you should think about before starting this project. Look up these words and concepts.: Amorphous solid, Crystalline solid (also known as crystal), Molecule, Solution, Compound, Saturated, Nucleation, Seed crystals.

Materials

  • Yarn or cotton string
  • Glass jar (a 14 oz jar works well)
  • Water
  • Tablespoon
  • Large plate
  • Granulated white sugar
  • Screw, or other small nontoxic object to use as weight
  • Wooden skewer, Popsicle® stick, or pencil
  • Tape
  • Saucepan
  • Stove
  • Measuring cups
  • Wooden mixing spoon
  • Potholders
  • Paper towel
  • Adult supervision
  • Optional: Food coloring
  • Optional: Concentrated food flavoring

Prep Work

Day 1: Seed the string
  1. Cut a string approximately two inch longer than the height of the glass jar.
  2. Soak the string in a cup of water for 5 minutes.
  3. Use your hand to squeeze the excess water from the string.
  4. Roll the string in one tablespoon of sugar on a plate. The string will be coated with sugar.
  5. Lay your sugar-coated string on a clean, dry plate overnight.

Day 2: Set up the jar
  1. Tie one end of your sugar-coated string to a screw or other small object that can serve as a weight. This weight prevents the string from floating in sugar water. It is ok if some of the sugar falls off while you are tying the string to the weight.
  2. Tie the other end of the string to a skewer, Popsicle® stick, or pencil. This stick will rest across the mouth of the jar and keep the string up.
  3. To adjust the length of the string, lower the weighted end of the string into the jar and rest the skewer across the mouth of the jar. Roll the skewer to wind the string until the weight is hanging approximately one centimeter (cm) from the bottom of the jar. Tape the string to the skewer so that the length of the string is fixed. Question: Why do you think the crystal should not touch the bottom of the jar?
  4. Take the skewer with string attached out of the jar and set it aside.
  5. Caution: Be sure to do steps 6-25 under adult supervision or with adult help!
  6. Heat enough water to fill the jar. When the water is boiling, carefully pour it into the jar. You might want to use a funnel to avoid spilling too much water.
  7. Let the jar full of hot water sit until your sugar-water solution is ready. Question: Why do you think it is important to preheat the jar?
  8. You will now make the sugar-water solution. Be extra careful; the sugar-water solution will get extremely hot and can cause a bad burn if spilled.
  9. Warm up ½ cup of water in a pot. (Note: if you are using jars that are larger than 14 oz, use ¾ cup of water, or, for even larger jars, 1 cup of water.)
  10. Turn the heat on to low.
  11. Add 1 cup of sugar to the water. (Note: add 1½ cups of sugar if you used ¾ cup of water in step 9, or 2 cups of sugar if you added 1 cup of water in step 9.)
  12. Mix with a wooden mixing spoon. Question: Why is it not advised to use a plastic or metal spoon?
  13. Stir the solution until you no longer see sugar crystals floating around in the water. Question: What do you think happens to the sugar?
  14. Turn the heat back up and wait until the sugar-water solution returns to a rolling boil. Make sure to keep stirring so the temperature is consistent throughout the solution. Caution: Be careful not to splatter! This sugar water is extremely hot and will burn if spilled on your skin.
  15. Remove the boiling sugar-water solution from the stove.
  16. Continue to add sugar 1 tablespoon at a time. Stir thoroughly after each added spoonful, making sure that the sugar is completely dissolved before adding another spoonful. The sugar is completely dissolved when you no longer see sugar crystals in the solution. To distinguish between the tiny little bubbles in the solution and undissolved sugar, you can stop stirring for a moment; the undissolved sugar crystals will settle to the bottom of the pan, but the bubbles will remain suspended throughout the solution. Question: Why do you think we need to have that much sugar dissolved into the solution?
  17. Keep adding sugar until no more will dissolve in the solution. If you think you have added too much sugar to your solution, do not worry. Keep stirring and if, even after a full 2 minutes of stirring, you have undissolved sugar at the bottom of your pot, return the pot to the stove. Heat the solution until it just begins to boil, then remove it from the stove. This should help you to get that last bit of sugar into the solution. Question: Why do you think we need to have all sugar dissolved into the solution?
  18. Optional: If you would like to explore what happens when you add a few drops of food coloring or flavoring (vanilla, mint, etc.) to your sugar-water solution, do that now. Question: Do you think you will end up with colorful or flavorful candy, or do you think these additives will stay in the water?
  19. Allow the sugar-water solution to cool for 5 minutes. Meanwhile, pour the hot water out of the glass jar. Caution: The jar will be hot, so use oven mitts or potholders to handle the jar.
  20. While you wait, choose a place to leave your jar undisturbed for a week. As large fluctuations in temperature can interfere with the crystallization process, avoid places that get direct sunlight or are near a heating or cooling vent. Also, remember that you will want to see what happens in the jar without moving it.
  21. After the sugar-water solution has cooled for about 5 minutes, pour the solution into the preheated glass jar. Caution: Be extremely careful when pouring the sugar-water solution; it is hot and will burn if spilled on your skin.
  22. Using potholders, move the hot jar to the place where you will leave it undisturbed for one week.
  23. Gently lower the weighted string into the jar.
  24. Securely tape the skewer holding the string to the edges of the jar to prevent the string from being accidentally jostled. Question: Why do you think it is important that the string does not move around in the jar?
  25. Loosely cover the jar with a paper towel to prevent dust and debris from flying in, while still allowing evaporation to occur. Question: Why would it be important to allow water to evaporate out of the water solution?

Days 3 to 6: Observe crystal growth

Look at your jar once a day but try not to move the jar or the string while you observe. Shining a flashlight through the jar can help see the growing crystals. Question: What do you see? Are there any crystals growing? Where on the string are the crystals? Are there crystals on places other than the string?

 

Day 7: Enjoy the candy
  1. After up to a week of growth, remove the string from the jar. If there is a layer of hardened sugar syrup coating the top of your jar, you can use a spoon to gently break that layer before pulling out your sugar crystal.
  2. Briefly rinse the rock candy crystal in cold water, then leave it on a paper towel for 30 minutes to dry.
  3. Observe your rock candy. Question: What does the rock look like? Does it remind you of something you have seen in nature, and if so, what? Is the rock thicker in certain places? Why would it form that way?
  4. Now you can eat your candy!

 

What Happened?

After a day or two, you probably saw crystals forming on the string; these crystals probably grew larger day after day.

When you stirred sugar into hot water, the sugar seemed to disappear. You could no longer see the sugar because it broke down into the tiniest sugar particles; the sugar dissolved in the hot water. These tiny sugar particles are so tiny that you cannot see them.

When this sugar-water solution cools, the dissolved sugar particles, which are continuously bumping into each other, start to occasionally stick together; this is the beginning of the crystallization process. Once several sugar particles are stuck together, they actively attract other sugar particles to join them. This is how the crystal “grows.”

You lowered a sugar-coated string into the solution. The little pieces of sugar on the sugar-coated string are meant to act as seeds; they attract other sugar particles to join them, so the sugar crystals grow on them.

You preheated the jars before adding the sugar solution. Adding your very hot sugar-water solution to a cold jar would result in a dramatic temperature change of the sugar solution. This sudden cooling might initiate the formation of small crystals along the glass. The small crystals would then act as seeds and that could disrupt the growth of your rock candy formation. To prevent this disruption, you warmed the jar before you added the hot sugar-water solution.

It is advised to use a wooden spoon to stir, not a plastic or metal one because a plastic spoon might melt in the sugar-water solution while a metal spoon might burn you when it gets hot.

Credit 

David B. Whyte, PhD, Science Buddies

The Chemistry of Clean: Make Your Own Soap to Study Soap Synthesis

Introduction

It’s not clear who first invented soap. There are documents suggesting that it was used by ancient Phoenicians over 5,000 years ago. Substances believed to be soaps have been found in ancient Egyptian ruins. It might have been invented independently in several regions at different times. An intriguing story about how the Romans learned to make soap involves the tradition of sacrificing animals on Mount Sapo. Parts of the sacrificed animals were burned as offerings to the gods. Fats from the burnt animal flesh mixed with ashes from the fires. When it rained, the Roman’s noticed that a substance formed in the pools of water that ran from the ashes that had been mixed with the animal fats. Upon experimentation, they learned that this new substance, later called soap, had useful properties, including the ability to clean surfaces. Chemists now refer to the chemical reaction for making soap as saponification, in honor of the discovery on Mount Sapo.

Soap is formed by mixing fats or oils with strong bases, such as sodium hydroxide. Sodium hydroxide is also called lye. The traditional way to make lye is to leach ashes with water. The ashes contain substantial amounts of sodium hydroxide, which dissolves in the water, forming a solution of sodium hydroxide. Before soap became available from large companies, people made their own by mixing animal fats with lye in a pot and boiling it. You could tell when it was “done” by taking a small amount of the mixture and adding it to some clean water. If there were droplets of fat on the surface of the water, the reaction was incomplete. More lye was added and the reaction continued. It was later discovered that the soap could be purified by adding salt to it. The addition of salt caused the soap to form a solid that excluded impurities, such as the sodium hydroxide. This soap was milder and suitable not just for washing clothes or pots, but also for use on skin. The figure shows the chemical reaction that is the basis for soap synthesis.

 

Figure 1. Saponification of a fat molecule. The bonds that connect the long chains of the fat molecule to the “backbone” are broken by the reaction of sodium hydroxide (and heat), yielding glycerol and three fatty-acid molecules (soap). The “acid” part of the fatty acid is the side with the oxygen (O) atoms. This end mixes well with water. The fatty part is the long chain of carbons, shown here as the crooked lines. This end mixes well with fats and oils. In the second step, the fatty acids are converted into relatively pure fatty-acid salts by the addition of sodium chloride.

 

Now to explain, chemically, how soap works to clean things. Fats mixed with strong bases are hydrolyzed into fatty acids. Fatty acids have the very useful property of having one end that mixes well with water (it is hydrophilic, or “water-loving”) and another end that mixes well with oils and fats (it is hydrophobic, or “water-hating”). The part that mixes well with water is the “acid” part. The part that mixes well with fats is the “fatty” part. This dual nature allows soaps to dissolve fat, grease, and dirt in water. Without soap, oil and water don’t mix. With soap, they do.

 

 

Making Soap: A Basic Chemical Reaction

Soap is the result of a basic chemical reaction between fats or oils and lye. The process of achieving the chemical reaction is called saponification. By carefully choosing a combination of quality oils, adding your favorite fragrance or essential oils, and swirling in a lively colorant, your handmade soap suddenly takes on a charming, rustic character.
There are two  basic methods for making soap at home.
  1. Melt and pour: This easy process involves melting pre-made blocks of soap and adding your own fragrance.
  2. Cold process: The cold process is the most common method of making soap from scratch using oils and lye.
Making soap with a melt and pour base is safe, easy, and convenient. The base has already gone through the saponification process, so you won’t need to handle lye. First, purchase pre-made blocks of uncolored, unscented soap “base” from a craft store or soap supplier. The soap base is then melted in a microwave or a double boiler. When the soap is fully melted you can add fragrance, color, and additives. Pour the mixture into a mold and the soap is ready to use when it hardens.
Each method has pros, cons, and variations. Review the two most popular methods to select your method.

To get started with melt and pour soap making, you’ll need a few tools after you purchase a soap base.
  • A microwave or double boiler
  • A heat-resistant bowl for the microwave
  • Measuring spoons and whisks
  • Fragrance, color, or additives, as desired
  • A mold
The most popular soap bases are white or clear glycerin. For a more luxurious soap, try a base made with goat’s milk, olive oil, or Shea butter. You’ll cut the soap base up into chunks to help it melt faster. If you use a microwave to melt the chunks, put the base in a microwave-safe bowl and stir at 30-second intervals until the chunks are liquid and smooth. Or melt in a double boiler over low heat, stirring until liquid and smooth. Then, allow the base to cool to 120 degrees Fahrenheit, then stir in colorants, fragrances, and additives of your choice. Finally, pour the mixture into your soap mold, wait a day until the soap is hardened and dry, remove from the mold, and your creation is ready to use.
There are a few tricks to know about when making melt and pour soap. The melted base will be thin, which means additives may sink to the bottom unless you wait until the base cools a bit before adding in. Melt and pour soap cools and hardens quickly so you’ll have to learn to time it right when using additives. If the base is too hot, it can burn and become gloppy and tough to work into a mold.
Some additives work better than others in melt and pour soaps. Try sandalwood powder or dried calendula flower petals for best results. Many herbs tend to change color in the soap. Other additives include exfoliants, fruit seeds, and milk powders.

 

Cold Process Soap Making Method

The cold process method is a little more complicated and takes longer than melt and pour soap. It also involves using lye, which is a caustic substance. To make cold process soap, you’ll heat your choice of oils in a soap pot until they reach approximately 100 degrees Fahrenheit. Then, you’ll slowly add a lye-water mixture and blend the soap until it thickens to trace. After the mixture reaches trace, add fragrance, color, and additives, then pour it into a mold. The raw soap takes about 24 hours to harden and a few weeks to cure before it’s ready to use.

To get started making cold process soap, be prepared to need more equipment and clean-up time than you would with melt and pour soap. Work where there is a heat source and access to water. There are several tools you’ll want to have on hand for this method of soap making, but begin with the basics:
  • Animal fats or vegetable oils
  • A pitcher of lye-water
  • A soap pot
  • Fragrance or essential oil, as desired
  • Natural or synthetic colorant, as desired
  • A mold to pour the raw soap into
  • Safety gear
You’ll need to have a cool, dry place where the soap can cure. Since this method of soap making includes the saponification process, you’re able to use fresh additives such as milk and fruit. Fresh additives can be included because of the high pH environment of the saponification process preserves the ingredients and prevents the formation of bacteria or mold. The texture of cold process soap is also thicker, which means you can use heavier additives that won’t sink to the bottom.
Take note that any vanilla ingredient might not be a reliable additive in cold process soap making because of the potential alcohol content, and it may turn your soap brown.

 

Safely Working With Lye

Lye is a caustic ingredient. When working with lye, wear protective gear including eye goggles, gloves, long sleeves, and pants to fully cover any exposed skin from spillage.

 

Questions

  1. What are other oils, besides coconut, that are used to make bath soaps?
  2. Based on your research, why is potassium hydroxide used instead of sodium hydroxide to make certain kinds of soaps?
  3. Based on your research, what is a micelle?
  4. What is the chemical name of the most common fatty-acid molecule found in coconut oil?
  5. How does the “split-personality” of a soap molecule make it a good cleaning agent?
  6. What is a triglyceride?
  7. The procedure for this science project uses 3-molar (3M) sodium hydroxide. What does the term molar mean?

 

Credits

David B. Whyte, PhD, Science Buddies

Color-changing Cabbage Chemistry

Introduction

What if you could take a single liquid, and change it into a rainbow of colors without using food dye. You can! In this activity, you will use red cabbage to make what is called an indicator solution. Indicator solutions can change colors depending on what you add to them. In this case, adding something acidic (like lemon juice) will change it to one color while adding something basic (like bleach) will change it to another. Try and see how many colors you can make using different household acids and bases.

Time: 45 minutes to 1 hour

Key Concepts: chemical reaction, acids, bases, pH indicator

 

  • A small red cabbage
  • Lemon or lime juice
  • Vinegar
  • Optional: Other foods to test, such as clear soda pop, baking soda solution, egg whites, tomatoes, cottage cheese
  • Small white paper cups, drinking glasses, or small white dish (at least 3)
  • Grater
  • Strainer
  • Optional: Large spoon
  • A boiling pot of water
  • Large bowls or pots (2)
  • Bleach cleaning product

 

 

Prep Work

  1. Children should wear goggles or other protective eyewear and adults should supervise and use caution when handling bleach because it can irritate eyes and skin.

Procedure

  1. Grate a small red cabbage. Put the grated cabbage into a large bowl or pot.
  2. Boil a pot of water. Use caution when handling the boiling water. Pour the boiling water into the bowl with the cabbage pulp until the water just covers the cabbage.
  3. Leave the cabbage mixture steeping, stirring occasionally, until the liquid is room temperature. This may take at least half an hour. The liquid should be reddish-purple in color.
  4. Place a strainer over another large bowl or pot and pour the cabbage mixture through the strainer to remove the cabbage pulp. Press down on the pulp in the strainer, such as by using a large spoon, to squeeze more liquid out of the pulp.
  5. In the bowl, you should now have a clear liquid that will either be purple or blue in color. (It should look darker after the pulp is removed.) This will be your indicator solution.
  6. Fill a small white paper cup, drinking glass, or small white dish with 1 tablespoon (tbsp.) of your cabbage indicator solution. What is the color of your indicator solution?
  7. Add drops of lemon or lime juice to the indicator solution until you see the solution change in color. Gently swirl the solution and make sure the color stays the same. Question: What colour did the solution become?
  8. The color of the solution will change depending upon how acidic or basic it is. This is based on the pH of the solution. pH is a numerical measure of how acidic or basic something is. A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. The solution will be the following colors based on its pH: Red indicates pH 2; Purple indicates pH 4; Violet indicates pH 6; Blue indicates pH 8; Blue-green indicates pH 10; Greenish-yellow indicates pH 12. In summary, acidic solutions should be red or purple in color, neutral solutions should be violet, and basic solutions should be blue, blue-green, or greenish-yellow in color.
  9. Based on its color, what is the pH of the lemon or lime juice solution?
  10. In another small white paper cup, add 1 tbsp. of your original cabbage indicator solution. Add drops of vinegar until you see the solution change color. Question: What color did the vinegar solution become? What is the pH of the solution? Is it an acid or a base?
  11. In a third small white paper cup, add 1 tbsp. of your original cabbage indicator solution. Handling it with caution, add drops of the bleach cleaning product until you see the solution change color. Question: What color did the bleach solution become, and what does this indicate about its pH? Is it an acid or a base?
  12. If you want to test the pH of other foods, again add 1 tbsp. of your original cabbage indicator solution to a small white paper cup and add drops of the food until you see the solution change color. If the food is not in liquid form, crush it or dissolve it in a small amount of water before adding it to the indicator solution. What color did the solution become, and what does this indicate about its pH, and whether it is an acid or a base?

 

Cleanup

Dilute the bleach solution with water before pouring it down a drain.

 

What Happened?

A solution with a pH between 5 and 7 is neutral, 8 or higher is a base, and 4 or lower is an acid. Lime juice, lemon juice, and vinegar are acids, and so they should have turned the indicator solution a red or purple color. Bleach is a strong base and so it should have turned the indicator solution a greenish-yellow color.

 

Digging Deeper

Acids are solutions that lose hydrogen ions, “donating” them to the solution, and usually taste sour. Some very common household solutions are acids, such as citrus fruit juices and household vinegar. Bases are solutions that pull hydrogen ions out of solution and onto itself, “accepting” them, and usually feel slippery. Bases have many practical uses. For example, antacids like TUMS are used to reduce the acidity in your stomach. Other bases make useful household cleaning products.

To tell if something is an acid or a base, a chemical called an indicator is used. An indicator changes color when it encounters an acid or base. There are many different types of indicators, some that are liquids and others that are concentrated on little strips of “litmus” paper. Indicators can be extracted from many different sources, including the pigment of many plants. For example, red cabbages contain an indicator pigment molecule called flavin, which is a type of molecule called an anthocyanin. Very acidic solutions will turn anthocyanin a red color, while neutral solutions will make it purplish, and basic solutions will turn it greenish-yellow. Consequently, the color an anthocyanin solution turns can be used to determine a solution’s pH (which is a numerical measure of how basic or acidic it is).

 

For Further Exploration

  • There are other plants that can be used to make pH indicators as well: red onion, apple skins, blueberries, grape skins, and plums. Which different sources of pigment produce the best indicators?
  • You can use an indicator solution to write secret messages. Just use full strength lemon juice to write an invisible message on paper and let the message dry. To reveal the message, paint indicator over the paper with a paintbrush.

 

Additional Resources

Links

Science Careers

Credits
Teisha Rowland, PhD, Science Buddies

Do-It-Yourself DNA

Introduction

Have you ever wondered how scientists get a sample of DNA from a plant, animal, or another organism? All living organisms have DNA. DNA, which is short for deoxyribonucleic acid, is the blueprint for almost everything that happens inside the cells of an organism — overall, it tells the organism how to develop and function. DNA is so important that it can be found in nearly every cell of a living organism. In this activity, you will make your own DNA extraction kit from household chemicals and use it to extract DNA from strawberries.

Time: 20-30 minutes

Key Concepts: DNA, genome, genes, biochemistry, DNA extraction
Materials:
  • Rubbing alcohol
  • Salt
  • Water
  • Strawberries (3)
  • Dishwashing liquid for hand-washing dishes
  • Measuring cup for liquids
  • Measuring spoons
  • Glass or small bowl
  • Funnel
  • Tall drinking glass
  • Cheesecloth
  • Re-sealable plastic sandwich bag
  • Small glass jar, e.g., spice jar or baby food jar
  • Bamboo skewer, available at most grocery stores. If you are using a baby food jar or a short spice jar as your small glass jar, you could use a toothpick instead of a skewer.

 

Prep Work

  1. Chill the rubbing alcohol in the freezer. You will need it to be very cold to do the activity.

Procedure

  1. Mix 1/3 cup (C) water, ½ teaspoon salt, and 1 tablespoon (tbsp.) dishwashing liquid in a glass or small bowl. Set the mixture aside for now. This is your extraction liquid, which is what you will use to extract (or remove) the DNA from the strawberries.
  2. Completely line the funnel with cheesecloth. Put the funnel’s tube into a tall drinking glass (not the glass with the extraction liquid in it). Set this setup aside for now.
  3. Remove the green tops from the strawberries and discard the tops. Put the strawberries in a re-sealable plastic sandwich bag and push out all of the extra air. Seal the bag tightly.
  4. With your fingers, squeeze and smash the strawberries for two minutes. How do the smashed strawberries look?
  5. Add 3 tbsp. of the extraction liquid, you prepared to the strawberries in the bag. Push out all of the extra air and reseal the bag. Question: How do you think the detergent and salt will affect the strawberry cells?
  6. Squeeze the strawberry mixture with your fingers for one minute. How do the smashed strawberries look now?
  7. Pour the strawberry mixture from the bag into the funnel. Let it drip through the cheesecloth and into the tall glass until there is very little liquid left in the funnel (only wet pulp remains). How does the filtered strawberry liquid look?
  8. Pour the filtered strawberry liquid from the tall glass into the small glass jar so that the jar is ¼ full.
  9. Measure out ½ C of cold rubbing alcohol. Tilt the jar and very slowly pour the cold rubbing alcohol down the side of the jar. Pour until the alcohol has formed approximately a one-inch deep layer on top of the strawberry liquid. You may not need all of the ½ cup of alcohol to form the one-inch layer. Do not let the strawberry liquid and alcohol mix.
  10. Study the mixture inside of the jar. The strawberry DNA will appear as gooey clear/white stringy stuff. Question: Do you see anything in the jar that might be strawberry DNA? If so, where in the jar is it?
  11. Dip the bamboo skewer into the jar where the strawberry liquid and alcohol layers meet and then pull up the skewer. Question: Did you see anything stick to the skewer that might be DNA? Can you spool any DNA onto the skewer?

What Happened?

When you added the mixture of salt and detergent (i.e., the dishwashing liquid) to the smashed strawberries, the detergent helped lyse (or pop open) the strawberry cells. This caused the cells to release their DNA into the liquid in the bag. At the same time, the salt helped create an environment where the different strands of DNA could gather together in a clump, making it easier for you to see them. (When you added the salt and detergent mixture, you probably mostly just saw more bubbles form in the bag, due to the detergent.) When you added the cold rubbing alcohol to the filtered strawberry liquid, the alcohol should have made the DNA come together and separate itself from the rest of the liquid. You should have seen the white/clear gooey DNA strands in the alcohol layer, as well as between the two layers. A single strand of DNA is extremely tiny, too tiny to see with the naked eye, but because the DNA clumped together in this activity you were able to see just how much DNA three strawberries have when combining all of their octoploid cells! (“Octoploid” means they have eight genomes, or sets of their genes.)

Digging Deeper

Whether you are a human, rat, tomato, or bacterium, each cell will have DNA inside of it (with some rare exceptions, such as mature red blood cells in humans). Each cell has an entire copy of the same set of instructions, and this set is called the genome. Scientists study DNA for many reasons. They can figure out how the instructions stored in DNA help your body to function properly. They can use DNA to make new medicines. They can genetically modify foods to be resistant to insects. They can figure out the suspect of a crime. They can even use ancient DNA to reconstruct evolutionary histories!

To get the DNA from a cell, scientists do a DNA extraction. There are many DNA extraction kits available from biotechnology companies for scientists to use. During a DNA extraction, a detergent will cause the cell to pop open, or lyse, so that the DNA is released into surrounding liquid. Then the DNA is separated from the rest of the liquid (a process called precipitation) by adding alcohol. In this activity, strawberries are used because each strawberry cell has eight copies of the genome, giving them a lot of DNA per cell. (Most organisms only have one genome copy per cell.)

For Further Exploration

  • You can try this DNA extraction activity to purify DNA from lots of other things. Grab some oatmeal or kiwis from the kitchen and try it again! Which foods give you the most DNA?
  • If you have access to a milligram scale (called a balance), you can measure how much DNA you get (called a yield). Just weigh your clean bamboo skewer and then weigh the skewer again after you have used it to fish out as much DNA as you could from your strawberry DNA extraction. Subtract the initial weight of the skewer from its weight with the DNA to get your final yield of DNA. What was the weight of your DNA yield?
  • Try to tweak different variables in this activity to see how you could change your strawberry DNA yield. For example, you could try starting with different amounts of strawberries, using different detergents, or using different starting sources of DNA (such as oatmeal or kiwis). Which conditions give you the best DNA yield?

Additional Resources

Links

Science Careers

Credits
Teisha Rowland, PhD, Science Buddies

A Candle Seesaw Balancing Act

Introduction

Do you love playing on a seesaw? Why is it that depending on where you sit on the beam, and the weight of the person on the other side, you either fly up into the air or fall down to the ground? And why is it so difficult to perfectly balance the seesaw? It can all be explained with physics! In this activity, you will investigate the balancing forces of a seesaw—with a seesaw made of candles!

Time: 20-30 minutes

Key Concepts: Physics, gravity, force, lever, mass

 

 

Materials

  • Two identical birthday candles
  • Strong tape
  • Needle that is longer than the candle’s diameter
  • Aluminum foil
  • Knife
  • Two glasses the same height
  • Lighter or matches
  • Adult helper
Prep Work
  1. Tape the birthday candles together at their ends, so that both wicks are facing opposite directions.
  2. Put a large piece of aluminum foil on your work area to protect it from any wax spills.
  3. Set the two glasses next to each other in the middle of the aluminum foil. The gap between the glasses should be small enough to place the needle across it.
  4. Take the needle and push it all the way through the side of the candle exactly where the ends of both candles meet. This should be exactly in the middle between both wicks. If it is too difficult to push the needle through the candle, try to heat the needle in a flame before you push it through the wax.
Procedure
  1. Place the candle in the gap between the glasses so that the parts of the needle that are sticking out on each side of the candle rest on the rim of each glass. Question: Can you see the similarities between your experimental setup and a seesaw?
  2. If your candle seesaw is unbalanced, change the location of the needle in the candle. Once the needle is placed exactly in the middle of the two candles, the seesaw should be balanced. Question: Why does the needle have to be exactly in the middle of the candle to balance the seesaw?
  3. Make sure that your surface is covered with aluminum foil along the entire length of the candle.
  4. Once the candle is balanced and doesn’t drop down on either side, ask your adult helper to carefully light up both candles. Don’t light both candles at the same time—wait for a couple of seconds before you light the second one.
  5. Watch how both candles burn and observe the movement of your candle seesaw. Question: What happens? If you see movement, can you explain why the candle seesaw is moving?
  6. Once the candles burn down by about one fourth, blow out both candles and cut the top (approximately 1 cm or about ½ inch) of one of the candles.
  7. Place the candle between the glasses again, so that the parts of the needle that are sticking out on each side of the candle rest on the rim of each glass. Question: Is the seesaw still balanced as before? Why or why not?
  8. Again, ask your adult helper to light both candles the same way as before.
  9. Watch the candles burn and observe what happens. Question: How are your observations different this time?
  10. Make sure to blow out both candles before they burn completely.

 

 

What Happened?

Did you notice that what you were building resembled a seesaw? Both candles taped together formed a long beam that was attached to the needle, which acted as the pivot (or fulcrum). The candle beam was able to rotate freely from one side to the other just like a real seesaw. As you don’t put any extra weight on the candle beam as you would on a playground seesaw, the only force pulling down on the beam is the weight of the candle itself. To balance the seesaw, it is important that both forces pulling down on each side of the beam are exactly the same. This is only true if the needle is placed exactly in the middle of the candle beam. If one side is slightly longer, this would also make it heavier and it would drop down as you might have observed. However, if the needle is placed in the middle, the gravitational forces pulling down on each side should cancel each other out and it should stay balanced.

This changes once you light the candles. When the candle is burning, a chemical reaction occurs that converts the candle wax to a gas. You probably also noticed that the solid wax turned into a liquid and dripped onto the aluminum foil. The wax lost through burning and dripping makes the candle shorter, and therefore, lighter. As this side of the candle beam becomes lighter, it moves upwards, while the other, heavier side drops down. The rotation is reversed once the other candle loses wax and becomes lighter again. The key to this seesaw movement is that both candles are not losing the same amount of wax at the same time. This is the reason why you have to light them one after the other. If both candles start burning at exactly the same time and lose the same amount of wax at the same time, the candle seesaw would stay balanced.

If you cut part of the candle on one side, the longer, now heavier side of the beam would dropdown. When you lit the candles, you probably noticed that the candle seesaw didn’t move at all, as the longer side will always be heavier while both candles are burning. However, if you would have only lit up the candle on the heavier side, you would have noticed that as soon as the candle burnt down enough to make it shorter and lighter, the seesaw dropped down on the other side.

Credits
Svenja Lohner, PhD, Science Buddies

Candy Diffusion Art: The Molecules Move!

Introduction

Here is a fun project you can try with leftover candy you have. You will make some amazing art using nothing but colored candy and hot water—and a little bit of science. Save some of your candy and get started!

Time: 10 minutes

Key Concepts: Chemistry, molecules, diffusion, gradient

Materials 
  • Hard-shelled colored candies, such as M&Ms® or Skittles®
  • Small plate
  • Glass or measuring cup
  • Warm tap water
  • Dishtowel or paper towels
  • Spoon
  • Sugar
  • Workstation than can tolerate spills and color dyes
  • Food coloring (optional)

Prep Work

  1. Arrange pieces of candy in a circle around the inner rim of the plate. Use at least two different colors, alternating them in groups of two or three.
  2. Fill a measuring cup or glass with warm tap water.

Procedure

  1. Slowly pour warm tap water into the middle of the plate, until it partially covers the candy (or fully, depending on how deep the plate is).
  2. Watch the plate closely for a few minutes. What happens?
  3. Empty and dry off the plate.
  4. Make a circle of candy around the plate again.
  5. Put a small pile of sugar (about a quarter teaspoon) directly in the middle of the plate.
  6. Slowly pour warm tap water near the center of the plate (but not directly onto the pile of sugar).
  7. Watch the plate closely for a few minutes. Question: What happens this time? Is it different from what happened the first time?
  8. Clean off the plate and repeat the test. Try different color patterns and/or arranging the candy (and sugar) in different shapes. What patterns and artwork can you make?

 

What Happened?

When you pour water onto the plate, the candy’s colored coating starts to dissolve in the water. As a result, you can see the colored dye diffuse towards the center of the plate. This diffusion can result in amazing, colorful rainbow patterns, as the colors remain mostly separate at first instead of bleeding together. You might have seen a “pie wedge” type pattern with different slices of each color you arranged around the rim.

When you put sugar in the middle of the plate something strange happens. The dye seems to hit an invisible wall in the water and stop diffusing at first, then diffuses much more slowly. This occurs because in addition to colored dye, the candy’s coating also contains sugar. Both the sugar and the dye dissolve into the water, forming a mixture called a solution. With your first test the sugar wants to spread out from where there is a high concentration of sugar (right next to the candy) to where there is a lower concentration of sugar (the middle of the plate). The whole solution (sugar and dye molecules) moves along this gradient from high concentration to low concentration. Although you can’t see the sugar from the candy coatings, you can see the colored dye. With your second test, however, there is already a lot of sugar in the middle of the plate—there is not a steep sugar gradient between the rim of the plate and the center. This prevents the sugar (and the dye) from spreading towards the center as rapidly. You might wonder “well, there are still no dye molecules in the middle of the plate, so shouldn’t the dye molecules keep diffusing, even if the sugar doesn’t?” That’s a good question! Different types of molecules diffuse at different rates in water. In this case the solution with the sugar molecules diffuses much faster than the dye molecules would on their own. This explains why, if you drop some food coloring into still water, it diffuses much more slowly than the dye from the candy. The food coloring does not contain any sugar.

If you watch the plate for a while, you might have noticed that the colors remain separated for quite some time. This can seem surprising—you might expect the colors to all blend together and turn a muddy brown. Remember, however, that it’s the sugar gradient that drives the diffusion. After the whole plate is filled up with colors, the sugar concentration is the same everywhere—there is no sugar gradient between the different colors. So the colors will continue to diffuse slowly due to the random motion of the molecules—but this process is much slower than the initial diffusion caused by the sugar gradient.

For Further Exploration

  1. Watch the plate for about five to 10 minutes. Do the colors continue to diffuse at the same rate they did initially?
  2. Leave the plate out all day and check on it periodically or let it sit overnight. How long does it take the colors to blend completely?
  3. Try the test with cold water instead of warm water. Do the colors diffuse at a different rate?
  4. Drop some food coloring into a plate of still water and watch how it diffuses. How is it similar to or different from the way the dye diffused from the candy? Can you figure out why?

 

Credits
Ben Finio, PhD, Science Buddies

DIY Sail Boats: Float or Sink?

Introduction 

It’s time to set sail! Even if you live nowhere near a lake or ocean, you will get to do some sailing in this science activity as you build your own toy sailboat. But first, you have to make sure your boat doesn’t capsize! Are you up for the challenge?

Time: 20-30  minutes

Key Concepts: Forces, weight, buoyancy, gravity, center of mass

 

Materials

  • Wine corks (3)
  • Rubber bands (2)
  • Toothpick
  • Several screws or nails
  • Craft foam, wax paper, or paper milk carton to make a sail
  • Aluminum foil
  • Sink, bathtub, or a large container you can fill with water. The container should be deeper than the length of your nails/screws.
  • Tap water

Prep Work

  1. Fill your container with water. Make sure you can put your longest nail/screw vertically into the water and completely submerge it.

Procedure

  1. Line up three corks (side by side, not end-to-end).
  2. Use two rubber bands to hold the corks together, forming a “raft.”
  3. Poke a toothpick into the center cork, so it sticks straight up. This is your boat’s mast (the part that holds the sail).
  4. Cut a square of thin waterproof material (see materials list – don’t use regular paper) to make a sail. It should be about 6 cm x 6 cm.
  5. Poke the toothpick through opposite ends of the sail (near the edges) to hold it in place. Your completed boat should look like this:
  6. You’ve made your first sailboat! Put it in the water. Blow on the sail from behind. Question: What happens?
  7. Now make a skinnier boat by removing the rubber bands and the two outer corks. Keep the sail in place. Rotate your sail 90 degrees so it matches the next picture.
  8. Put your new sailboat back in the water. Question: What happens?
  9. Uh-oh! Your sailboat probably fell over! That’s not good. To fix it, try adding a keel. Stick a nail or screw into the bottom of the boat, directly under the sail.
  10. Try putting the boat back in the water. If it doesn’t stay upright, keep adding nails or screws (in a straight line with the first one) until it can float without tipping over.
  11. Now try blowing on the sail again. Question: What happens? Does your boat move in a straight line?
  12. Right now, your keel is made of one or more nails/screws, but they are not connected to each other. Cut a rectangular piece of aluminum foil and tightly wrap it around the nails/screws to make a “fin” shape.
  13. Put your boat back in the water and try blowing on the sail again. Try making different boats and compare their performance. Question: Which design is the most stable? Which one goes the fastest?

What Happened?

Your first sailboat was probably pretty stable because it was very wide (made from three corks). However, when you removed two corks to make it skinnier, your sailboat probably became unstable and tipped over. It’s similar to standing with your feet tight together instead of spreading out slightly—it’s harder to balance. When you added nails/screws to the bottom of your sailboat, you lowered its center of mass and made it more stable. However, individual vertical nails don’t do a very good of job pushing against the water—the water can flow right around them. That means they don’t do a good job of making the boat go straight. If you blew on the sail, your boat might have curved off to one side or spun in circles. When you wrapped the nails in aluminum foil, you made the shape more like a fin. It can cut through the water very easily in one direction but provides a lot of resistance against the water in the other direction. That makes it easier for your boat to move forward, and harder for it to move sideways. This is why real sailboats can be long, skinny, and have tall sails—they have a part called the keel that prevents them from tipping over and helps them go straight!

Credit

Ben Finio, PhD, Science Buddies

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