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					Sticky Sneakers                             L2          Sticky Sneakers
      S 8.2.a, 8.9.c
                                                             S 8.2.a, 8.9.c

Students conduct an investigation to see the
effect of friction on a moving object.                  Problem
                                                        Friction is a force that opposes an object’s
                                                        motion. Friction can be useful. For example,
Prepare for Inquiry                                     friction between sneakers and the ground can
                                                        help an athlete to start and stop running. How
Key Concept                                             does the amount of friction between a sneaker
Sneaker soles can be used to illustrate                 and a surface compare for different brands of
friction.                                               sneakers?

Skills Objectives                                       Skills Focus
After this lab, students will be able to                controlling variables, interpreting data
• control variables in an investigation of                                                                        2. Prepare a data table in which you can record
                                                                                                                     each type of friction for each sneaker.
  friction                                              Materials                                                 3. Place each sneaker on a balance. Put masses
• interpret data to determine if the type of            • three or more different brands of sneakers                 in each sneaker so that the total mass of the
  sneaker is related to the type of friction            • 2 spring scales, 5-N and 20-N, or force sensors            sneaker plus the masses is 1,000 g. Spread
  observed                                              • mass set(s) • tape • 3 large paper clips                   the masses out evenly inside the sneaker.
                                                        • balance
        Prep Time 30 minutes
        Class Time 40 minutes                           Procedure                                                 4.         Tape a paper clip to each sneaker and
                                                         1. Sneakers are designed to deal with various                 attach a spring scale to the paper clip. (If you
Advance Planning                                            friction forces, including these:                          are using force sensors, see your teacher for
Assemble the spring scales, paper clips,                    • starting friction, which occurs when you                 instructions.)
tape, balance, and mass sets. Bring in an                      start from a stopped position                           To measure
                                                            • forward-stopping friction, which occurs                  • starting friction, attach the paper clip to
assortment of sneakers and ask students                                                                                  the back of the sneaker
                                                               when you come to a forward stop
to volunteer their sneakers.                                • sideways-stopping friction, which occurs                 • forward-stopping friction, attach the
                                                               when you come to a sideways stop                          paper clip to the front of the sneaker
Safety                                                                                                                 • sideways-stopping friction, attach the
    Review the safety guidelines in                                                                                      paper clip to the side of the sneaker
    Appendix A.
Teaching Resources                                                                                     Data Table
  Laboratory Manual
                                                                Sneaker       Starting Friction (N)         Sideways-Stopping          Forward-Stopping
  • Sticky Sneakers Student Worksheets                                                                      Friction (N)               Friction (N)

                                                                    A
Guide Inquiry
                                                                    B
Invitation
Have a student wearing sneakers
demonstrate three types of friction forces:
stopping, starting, and sideways. Ask: What             378 ◆
does friction depend on? (Sample answer:
Friction depends on the kinds of surfaces
involved and how hard the surfaces push
                                                 Introduce the Procedure                                     Troubleshooting the Experiment
together.) Have students discuss how
                                                 Demonstrate how to zero and use a spring                    • Students should zero the spring scale each
different kinds of sneakers might have
                                                 scale. Show students how to measure the                       time it is used. If the spring scale is
different kinds of friction.
                                                 force of sliding friction with a spring scale by              calibrated in grams, multiply by 0.01 to
                                                 pulling an object with a slow, constant                       obtain the approximate value in newtons.
                                                 motion. Tell students to pull an object                     • The spring scale should not be angled to
                                                 forward to measure forward-stopping                           the side or up and down while it is used, or
                                                 friction and sideways to measure sideways-                    the measurements will not be accurate.
                                                 stopping friction.




378
                                                                                                              Expected Outcome
                                                                                                              Results will vary depending on the type of
                                                                                                              sneakers.
                                                                                                              Analyze and Conclude
                                                                                                              1. The controlled variables are the adjusted
                                                                                                              masses of each sneaker at 1,000g. The
5. The force necessary to make the sneaker             4. Drawing Conclusions Do you think that using         manipulated variable is the sneaker; the
   start moving is equal to the starting friction         a sneaker with a small amount of mass in it is a
   force. To measure starting friction, pull the          fair test of the friction of the sneakers? Why or
                                                                                                              responding variable is the amount of
   sneaker backward until it starts to move. Use          why not? (Hint: Consider that sneakers are          friction.
   the 20-N spring scale first. If the reading is          used with people’s feet inside them.)               2. Friction is a force that acts in the opposite
   less than 5 N, use a 5-N scale. Record the
   starting friction force in your data table.
                                                       5. Inferring Why did you pull the sneaker at a         direction of motion. So, just as the sneaker
                                                          slow speed to test for stopping friction? Why       begins moving the spring scale shows the
6. To measure either sideways or forward stop-            did you pull a sneaker that wasn’t moving to
   ping friction, use the spring scale to pull each       test starting friction?
                                                                                                              amount of friction opposing motion.
   sneaker at a slow, constant speed. Record the       6. Drawing Conclusions Can you identify a              3. Students’ answers will depend on the
   stopping friction force in your data table.            relationship between the brand of sneaker           types of sneakers tested. In general running
7. Repeat Steps 4–6 for the remaining sneakers.           and the amount of friction you observed? If         sneakers have more starting friction,
                                                          so, describe the relationship. What do you          basketball sneakers exert more forward-
Analyze and Conclude                                      observe that might cause one sneaker to grip
                                                                                                              stopping friction, and tennis shoes exert
1. Controlling Variables What variables are               the floor better than another?
                                                                                                              more sideways-stopping friction.
   controlled? Explain your answers. What are          7. Communicating Choose one of the brands
   the manipulated and responding variables?              of sneakers that you tested. In a paragraph,        4. No, in actual use there is much more mass
   Explain your answers. (See the Skills Hand-            explain why this sneaker is the best one to         in the sneakers.
   book to read about experimental variables.)            wear while playing a particular sport or
                                                          activity. Be sure to include the results of this    5. You pull the sneaker at a slow speed to test
2. Applying Concepts Why is the reading on
                                                          lab in your explanation.                            stopping friction because your sneaker is
   the spring scale equal to the friction force in
   each case?                                                                                                 sliding slowly along the ground or floor
3. Interpreting Data Which sneaker had the
                                                      Design an Experiment                                    when you stop running. You pull a sneaker
   most starting friction? Which had the most         The strength of the friction force is determined        that is not moving to test starting friction
   forward-stopping friction? Which had the           by both the design of the sneaker and the type of       because your sneaker is not moving when
                                                      surface it presses against. Design an experiment
   most sideways-stopping friction?                                                                           you start running.
                                                      to find out how various types of surfaces affect
                                                      the force of friction acting upon the sneaker.          6. Students’ answers may state that one
                                                      Obtain your teacher’s permission before carrying        brand of sneaker provides better traction
                                                      out your investigation.                                 than another because the soles are made of
                                                                                                              different materials or have different tread
                                                                                                              designs.
                                                                                                              7. Students’ choice of a sneaker for a
                                                                                                              particular sport should reflect their
                                                                                                              knowledge of actions in the chosen sport
                                                                                                              that would be best completed with the
                                                                                                              sneaker with the appropriate starting
                                                                                                              friction, sideways-stopping friction, or
                                                                                                              forward-stopping friction from the table
                                                                                                              comparing their frictions.

                                                                                                    ◆ 379     Extend Inquiry
                                                                                                              Design an Experiment Students should
                                                                                                              suggest different surfaces such as wood,
                                                                                                              concrete, grass, or clay used for various
                                                                                                              sports. They should choose one brand of
                                                                                                              sneaker as the controlled parameter and
                                                                                                              different surfaces as the variable parameter.




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