Workshops: Skimmer Regatta 4
Air and Motion
Students test sail shapes and sizes and add the sail that works best to their skimmer
- Summarize how the shape and size of a sail can affect a boat's movement
- Experiment and use data to choose the best sail shape, size, and position to move the skimmer as far as possible with a given air supply.
SCIENCE BACKGROUND CAPSULE
The stiff sails on the Explore activity boats change the flow of air. Air pressure builds behind the sail and pushes the sail and, consequently, the boat forward. For real sailboats with flexible sails designed to fill out into a wing shape, there is a reaction force which results from redirecting the moving air. This reaction force and the increase in air pressure drive the boat. The wind exerts a push against the back of the sail. The action of the wind blowing across the curved front surface of the filled-out sail creates a reduced pressure much like the lift force that keeps an airplane up. The factors that affect a sailboat's speed and stability are the force and direction of the wind and the size, shape, and balance of the sailboat.
Have students complete Steps 1-5 of the Explore activity in their teams. Make sure students make the boats and sails correctly and that every student has a record sheet or a copy of the Skimmer Regatta Design Team Log. Students should not use the air pump for Explore.
Have a student read Challenge! aloud. Tell students they have five minutes to work on the Challenge! activity. After five minutes call an all-class Think Tank meeting.
THINK TANK MEETING
- Ask one student from each team to draw on the chalkboard the sail shape that worked best (boat went farthest without tipping over) for their team. Also ask for a sampling of shapes that did not work well to be drawn.
- Discuss why some shapes worked better than other shapes. Explain that the sails in the Explore boats caught the "wind." The caught air built up pressure against the said and pushed the sail and, therefore, the boat forward. You might want to introduce the concept of constants and variables by explaining that by using identical boats in Explore, they were able to test how changing just a sail's shape affected the boat's movement.
- Point out that a sail's shape determines how much wind will be caught and where the push will be. Tell students that the higher up the sail the wind is caught, the more likely it is that the boat will tip over. Draw two triangles on the chalkboard, one with a point at the top and one with a point at the bottom. Ask students to pick which shape would make a better sail, and have the class discuss why this choice is correct.
- Ask students where the air pushed the most on the different sail shapes they made. Have them relate their answers to the distance the boat was able to travel and the boat's stability with each sail shape.
- Have students from each team compare their smallest and biggest sails from the Challenge! activity. Allow them to tell about their experience. Lead students to understand that, in general, the bigger the sail, the more wind it can catch to push the boat. However, if a sail is too big, it will make the boat tip over. Smaller sails have advantages because they make the whole boat weigh less, but, if a sail is too small, it will catch very little wind and the boat will move slowly.
- Have one student read the introduction of the investigate section. Check for students' understanding. Tell students to return to their teams and investigate to find the best the best combination of sail size, shape, and position to move their skimmers. Remind copy and complete the Design Choice Records. You may choose to have students use the record sheets found in the Skimmer Regatta Design Team Log.
Circulate among teams to check on their progress. Encourage cooperative problem solving, creative experimentation, and neat and thorough record keeping. Make sure everyone gets to participate.