What Do You Think As students answer these questions ask them to think of the

# What do you think as students answer these questions

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What Do You Think? As students answer these questions, ask them to think of the shoes they wear daily and how they are different from the sports shoes they wear on the field. You might want to remind them that this is the time for them to write their responses without any hesitation. It is important that at this stage students discuss answers among themselves. Facilitate their discussion and make sure that your students are engaged in the process of preparing for the concepts they are about to learn. Teaching Tip Although using a shoe may not appear to be the most sanitary method of performing this activity, the students’ enthusiasm for it more than makes up for this aspect. Keeping a spray can of deodorant/disinfectant handy is usually a good idea. If the students do not list the weight of the shoe as a variable, ask them if a heavy crate is easier or harder to push across a floor. 1.b) Some variables the students may come up with include shoe size, tread style, shoe brand, weight of shoe, whether the shoe is high or low cut, etc. The students should quickly realize that if they are to use just one shoe, factors such as size, brand, etc., would not be variables for that shoe. They may also think that the “weight” (mass) is not a variable, but point out that objects can easily be slipped inside the shoe to increase its weight. The students’ design should show how a variable might affect the shoe’s frictional force. Check it for safety and feasibility using available equipment. Investigate 1.a) Answers will vary depending on the brand of shoe used and the size of the shoe. If you wish, you may use blocks of wood; some instructors prefer the increased precision. Students really like using shoes though.
Chapter 2 Physics in Action Active Physics 416 NOTES
Active Physics 417 CHAPTER 2 Section 7 Frictional Forces: The Mu of the Shoe 2.a) Students should record a data table in their logs that includes mass, force of spring scale, surface type, etc. Students should also realize that graphing the data will be a good analysis tool. 3.a) Students should record the surface type. Surfaces may be varied by taping sandpaper or rubber mats to the lab tables, or the students may use the floor. Using a carpeted area may prove problematic, since the loops of the carpet will provide a very uneven frictional force as they bend under the applied force. 3.b) Encourage students to strive for consistent results. Hooking the scale to a low point on the shoe helps make it slide rather than tilt. Ask them if they notice whether the force necessary to start the shoe moving is more or less than the force necessary to keep it moving at a slow, constant speed. Students should look for a consistent average reading on the spring scale.
Chapter 2 Physics in Action Active Physics 418 3.c) μ results will vary. Generally, the coefficient of friction should be less than 1, and in the region of 0.3-0.8.

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• Fall '12
• E.Smith

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