Have you ever watched a sailboat or a windsurfer zip along without the help of a motor? You're witnessing the power of the wind. But getting speed from the wind is all about harnessing it well. And knowing just a little bit about how pressure works can help you design a better boat. Then you can challenge different sail designs to a breath-powered boat race. Anchors aweigh!
Air is made up of tiny particles called molecules. When you blow on your hand, you can feel a breeze because you are pushing the air molecules with your breath. The force of air molecules pushing against the surface of an object in scientific terms is known as "pressure." In this activity you will explore firsthand how air pressure can make objects move.
- Materials for at least two similar boats, such as aluminum foil; Styrofoam cartons; pieces of pool noodle
- Materials for at least two similar sails, such as paper or foam craft sheets
- A long, straight aquatic racetrack (Some items that work well for this include water-filled, capped vinyl rain gutters—which can be found at home improvement stores—long plastic tubs or a bathtub. A large body of still water, such as a swimming pool with a straight edge, can work, too.)
- Craft sticks
- Water to fill your racing spot, if necessary
- Someone to act as the official for the race
- Area without too much wind
- Build at least two identical boats using materials that are lightweight and waterproof, such as from aluminum foil or pieces of pool noodles. Why does the boat need to be lightweight? Why should they be matching?
- Next, make the masts by taping straws or craft sticks perpendicularly to the boats or by carefully cutting a slit into pool noodle pieces and inserting the craft sticks. Each boat gets one mast.
- Now it's time to design the sails! What shapes might help the boat move the fastest?
- Cut a piece of lightweight paper or foam craft sheet to act as the mainsail for each boat. No need to match this time! In fact, try different shapes to see what works best.
- Carefully poke holes in either end of the sheets and slide the sails onto the mast of each boat through the holes—or tape them to the masts.
- Optional: Decorate your boats in any way you'd like.
- Prepare the racetrack and get ready to race!
- Place the first boat at the starting line and be prepared with a straw to start blowing on your boat's sail. Why do you think it is important to find a spot without too much wind for this test?
- When the official says, "Go!" he or she should start the stopwatch. Start blowing through a straw aimed at the first boat's sail. Follow the boat down the track and blow at the sail as you go, but don't use the straw itself to push the boat forward! Have the official stop the stopwatch as soon as the boat reaches the designated finish line of the track. How long did it take for the boat to get to the end of the track? How many times did you have to blow through the straw? Did you boat seem to sail easily?
- Next it's time to try out the second boat! After you've caught your breath repeat the procedure. Which boat got to the finish line faster? Did they sail differently?
- Extra: You can challenge a friend or family member to a race. If you don't have two identical tracks to race simultaneously, you can each compete in a speed trial with the stopwatch to see who can get the fastest time. What variables other than sail or boat designs might be at play when racing against another person?
- Extra: How much do you think your sail size made a difference? Try the activity again by building boats with sails of different sizes but similar shapes. How big or little of a sail was the most successful? Why do you think that is?
- Extra: How fast can you get your boat to go? Try out sails of all different shapes, sizes and materials. What was the best combination of size, shape and material?
Observations and results
Air pressure moves the boat because more force is being exerted on one side of the boat than the other. The harder you blow, the faster the air molecules move and the more pressure you put on the boat’s sail. Your breath is acting just like wind does on real boats!
More to explore
How It Works: Sailboats, from the Smithsonian Institution
The Physics of Sailing, from QUEST
Sailing, from PBS Kids
Design and Race Boats, from the Museum of Science and Industry, Chicago
This activity brought to you in partnership with Museum of Science and Industry in Chicago