Friction*

Teacher Version(.doc)

Student Version(.doc)

• Grade Level(s):  6th, 7th, 8th
• Primary Focus: Science; NC Standard Course of Study Areas: 7th 6.03
  • (Key Concepts: Newton’s Law, Force, Friction)
• Secondary Focus: Math; NC Standard Course of Study Areas: 6th 1.07; 7th 1.03, 4.01; 8th 1.02, 4.01
  • (Key Concepts: Flexible problem solving and using data (box plots, scatter plots, and histograms)
• Computer/Technology Skills: Calculators, Probeware, Data Visualization; NC Standard Course of Study Areas: 7th 1.10, 2.02, 3.01, 3.02, 3.05
• Essential Question:  Why do the shoes you wear make a difference for activities such as basketball, skateboarding, or salsa dancing? What is friction and how does it relate to force?
• Summary of Activity:  Students will measure the frictional force, in Newtons (N), as different shoes are pulled across a surface.
• Cognitive Teaching Strategies: Students will measure sliding friction with shoes with different soles, make predictions about surfaces, and test the predictions.
• Materials:
  • TI-84 Plus Silver graphing calculator
  • EasyData application
  • EasyLink interface
  • Vernier Dual-Range Force Sensor
  • Various shoes (athletic, dancing, clogs, etc.) 
  • paper clip 
  • tabletop
  • Linoleum floor 
  • Other surfaces (skateboard deck?) 

Part I: Initial Procedure

1. Illustrate proper technique for pulling a shoe across a surface with the Force Sensor before the experiment. Remind students not to pull the block too fast.
2.  Attach the utility handle to the end of the Force Sensor. Attach the force sensor to the EasyLink. Set the Force Sensor range switch to 10 N. Attach the EasyLink to the calculator. The calculator should turn on and launch EasyData software.
   1. Start the EasyData application, if it is not already running.
   2. Reset the application by selecting file->new.
   3. Select  from the Main screen, then select Time Graph…
   4. Select  on the Time Graph Settings screen.
   5. Enter 0.05 as the time between samples in seconds and select .
   6. Enter 60 as the number of samples and select .
   7. Select  to return to the Main screen.
   8. How many seconds will this experiment run?
3. Zero the Force Sensor. 
   1. Lay the Force Sensor on the tabletop with the side opposite from the wire on the table.
   2. Select  from the Main screen, and then select Zero…
   3. Select  to zero the Force Sensor.
4. Choose a shoe. Partly straighten a paper clip—leaving a hook at each end. Use the paper clip to attach the shoe to the Force Sensor.
5. Slowly pull the shoe across a table with a smooth surface. Hold the Force Sensor by its handle and pull it towards you. The Force Sensor should be held parallel to and about 1 cm above the surface. Once the wooden shoe is moving at a steady rate, select  to begin data collection.
6. Determine and record the force used to pull the shoe.
   1. When data collection is complete, a graph of force versus time will be displayed. Select , and then select Statistics…  
   2. Before moving the cursor, select  to set the left bound at 0 s.
   3. Move the cursor to the right edge of the graph and select .
   4. Record the mean (average) force (in N).
   5. Select  to return to the graph.
   6. Select  to return to the Main screen.
7. Repeat Steps 5–6 as you pull the shoe over the floor. 

Part II: Predicting Friction

1. You will measure friction with other shoes.  In the space provided in the data table, predict the order of friction for these shoes and surfaces—from lowest to highest.
2. Repeat Part I: Steps 5–6 for each of the shoes and surfaces.

Instructional Strategies:

1. Heavier shoes may be easier to drag across surfaces.  You may wish to supply some clean rolled up socks to stuff into the shoes.
2. You  may wish to lead the students in a discussion about the weight of the shoes and how that affects the experiment.

Additional Resources for this Lesson:

• Friction (from BBC Science Clips) gives a simulation of a car traveling on a track.  The track surface can be changed.
• Friction in our Lives (from Discovery School) provides another experiment for students using toy cars.

Re-teaching and Enrichment Strategies:

1. Test the friction of other surfaces, such as glass, metals, rubber, and different fabrics.
2. Investigate how frictional force varies with contact area and mass.
3. Design an experiment to test methods of reducing friction. 

Data Collection and Analysis:

 

HYPOTHESIS:

 

DATA:

Part I  Shoe on two surfaces
Type of shoe
Surface	Table		Floor
Force (N)

Part II  Predicting friction
Predicted order of values for 3 shoes
(Lowest)		(Highest)

Surface	Shoe 1	Shoe 2	Shoe 3
Table	N	N	N
Floor	N	N	N

QUESTIONS:

1. What is the effect of surface roughness on friction? 
2. How did you decide the order of your predictions in Part II? 
3. How good were your predictions? Explain. 
4. Give two examples of situations where friction is helpful. 
5. Give two examples of situations where it is best to reduce friction.
6. Summarize the results of this experiment.

DISCUSSION:

Why do the shoes you wear make a difference for activities such as basketball, skateboarding, or salsa dancing? What is friction and how does it relate to force?

*Adapted from: Volz, D., & Sapatka, S. (2000). Middle School Science with Calculators. Beaverton, OR: Vernier Software & Technology.