Skimmer Regatta 2

Friction and Motion

Students determine the best surface on which to race their skimmer

• Define friction as the force that slows movement when two objects rub against each other.
• Experiment and use data to find the surface over which the skimmer will move as far as possible with a given supply of air.

When surfaces move against one another, a force called friction resists motion. All moving objects, including fluids such as air and water, have friction between them and any surface they touch. Different surfaces create different amounts of friction. If there is not a lot of friction between an object and the surface over which it moves, the object moves easily. In general, as friction increases, ease of movement decreases. On way friction can be reduced is by lubricating the surfaces between moving objects.

In Explore, students move a wind-up walking toy over different surfaces and then change the surface of their toy's feet to observe the effects of friction on the toy's speed and stability. In Investigate, students move the skimmer over different surfaces to observe the effects of friction on the skimmer's ability to move as far as possible. Using information obtained from Skimmer Regatta 1, students will choose the surface over which their skimmers will move the farthest when powered by a push of air. All surfaces increase the distance the skimmer travels, but most students will find that the waxed paper allows the skimmer to move the farthest with the given air supply.

Have students complete Steps 1-5 of the Explore activity in their teams. Be sure every team sets up the strips properly and that each student has a record sheet or a copy of the Skimmer Regatta Design Team Log.

Have a student read Challenge! aloud. Tell students they have eight minutes to work on the Challenge! activity. After eight minutes call an all-class Think Tank meeting.

1. List each surface on the chalkboard. Have students describe each surface listed. [Smooth, rough, sticky, slimy] Also have them describe the surface of the toy's original "shoes." Have them refer to their record sheets to describe how the toy moved over each surface.
2. Discuss the results of the Challenge. Ask students what kind of shoes enabled the toy to move fastest and steadiest. Ask students what they think made some shoes work better than others.
3. Help students understand that the shoes have different surfaces that come in contact with the different strips. Tell the students that friction occurs when two surfaces move across each other. Have them rub their hands together to illustrate the pull and resistance of friction.
4. Ask students to name and describe some other surfaces they touch each day. [Air (smooth); water (smooth); clothes (smooth or rough); food (rough, sticky, or smooth); books (smooth); furniture (smooth or rough); toys; sports equipment; and so on] Discuss whether these surfaces create a lot of friction or a little.
5. Tell students that there is always friction between two touching surfaces. Friction "fights" the force that makes an object move. When engineers want to move an object a particular distance or at a particular speed, they have to take friction into account. For example, when engineers deign sailboats, they investigate friction between the bottom of the boat and the water.
6. Explain that while too much friction makes it hard for an object o move, sometimes too little friction makes it hard to move, too. For example, riding a bicycle on grass is difficult because there is too much friction, but it is also hard to ride on ice because there is too little friction. Have students tell which surfaces in Explore had too much friction with the walking toy and which had too little.
7. 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 surface to use in the Skimmer Regatta. In Step 2, place the straws about 3 or 4 cm apart and brace the books against them. Remind students to read each numbered question, experiment to find the answer, and copy and complete the Design Choice Record. 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. Check that students are calculating the average distance correctly. Make sure everyone gets to participate.