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
- Wine corks (3)
- Rubber bands (2)
- 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
- Fill your container with water. Make sure you can put your longest nail/screw vertically into the water and completely submerge it.
- Line up three corks (side by side, not end-to-end).
- Use two rubber bands to hold the corks together, forming a “raft.”
- Poke a toothpick into the center cork, so it sticks straight up. This is your boat’s mast (the part that holds the sail).
- 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.
- Poke the toothpick through opposite ends of the sail (near the edges) to hold it in place. Your completed boat should look like this:
- You’ve made your first sailboat! Put it in the water. Blow on the sail from behind. Question: What happens?
- 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.
- Put your new sailboat back in the water. Question: What happens?
- 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.
- 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.
- Now try blowing on the sail again. Question: What happens? Does your boat move in a straight line?
- 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.
- 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?
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!
Ben Finio, PhD, Science Buddies