Energy, Machines, and Motion
Part One: Energy
Lesson 6: The Force of Friction
In Lesson 6 students explore the concept of sliding friction as a force in three different inquiries. Students will investigate the frictional force of a wooden block when you change the surface it is being pulled across, the amount of weight that is being pulled, and the orientation of the block as it is being pulled.
Focus Question: What are the factors that affect the force of friction?
3. Lesson Set-up and Management
EALR 2: Inquiry
Core Content: Questioning and Investigating
6-8 INQC Collecting, analyzing, and displaying data are essential aspects of all investigations.
6-8 INCD For an experiment to be valid, all (controlled) variables must be kept the same whenever possible, except for the manipulated (independent) variable being tested, and the responding (dependent) variable being measured and recorded. If a variable cannot be controlled, it must be reported and accounted for.
6-8 INCF It is important to distinguish between the results of a particular investigation and general conclusions drawn from these results.
EALR 4: Physical Science
Core Content: Balanced and Unbalanced Forces
6-8 PS1B Friction is a force that acts to slow or stop the motion of objects.
- Students learn friction is the force that resists motion between two surfaces in contact with each other.
- Students determine if different surface types affect the amount of friction on a wooden block.
- Students determine if different weight will affect the amount of friction on a wooden block
- Students determine if a block with the same weight and surface type will not be affected if you change the orientation or surface area of the block.
3. Lesson Set-Up and Management
Materials:
- Students will be given a different spring scale that measures greater forces. The increments of this tool are different from the first spring scale they used. Consider spending a few minutes discussing the differences.
- Students will have five different surface types to test, wooden
table, wax paper, paper towel, fine sandpaper, and course sandpaper.
Have a place where all surfaces types are set up for students to see.
Place all five surface types side by side.
You could include placing tape to outline
the area of the wooden table top as well.
- The illustration in the student guide shows the different surface types taped on the ends. Consider taping the material down on the side so it does not affect the test.
- In Inquiry 6.3 students place a rubber band around one wooden block to
change the surface area of the block being pulled. Consider placing the rubber
band differently so the long skinny side is being tested. This side has been
sanded the same as the orientation of Inquiry 6.1 and 6.2 keeping a variable
controlled more closely.
Inquiry 6.2 students will add blocks to change the load. Have students measure force with the smaller spring scale first. If the force is too large, switch to the other spring scale. Inquiry 6.3 students will change the orientation of the load. This change results in a smaller surface area. Our class decided to use this orientation rather than the orientation of Figure 6.3 because the sides have been sanded the same. This is decision you and your class may consider. You will need to add a rubber band so the block can be pulled horizontally.
Student Management:
- As students begin to pull on the blocks during each inquiry they will experience a static force (more force to get the block started). You will need to let them practice pulling the force at a constant rate so they get a more accurate reading of the force required to pull the block across the surface types.
- Students will be keeping track of data from each of the three investigations. Make sure you are helping students interpret the data that they collect during each inquiry.
- After the third inquiry students will be asked to summarize all of the data. Students will want to make sure they have results for each inquiry in their notebooks
- During Inquiry 6.2 students will not collect all of the data for all of the different weights and surface types. You will need to devise a system of collecting the data and recording it for the entire class.
- Consider creating an Excel document for students to add their “team” data for Inquiry 6.2. This can be quickly averaged, printed and pasted into a student notebook.
- Lesson 6.3 students will gather data with only one block pulled across different surface types with two different orientations. To move through the lesson more quickly have different groups gather data with only one surface type, bringing back data to the group.
- The attached documents are data tables that have been created and used by middle school students:
Writing Support:
- In the Getting Started section students make a list of what they
know or think they know about friction in their notebook. Consider
using a table to have students think about how friction is helpful or
not helpful.
How Friction Works For You
How Friction Works Against You
- Students will need to know what variables are being kept the same
and the variable that is being changed for each of the three
inquiries. Students may have more success if you create a chart for
each of the three inquiries. The following chart is an example of what
could be placed at the beginning of each of the three inquiries:
Variables for Inquiry 6.1
Controlled Variables
Manipulated Variable
Responding Variable
Same block
Same way of taping each surface type
Same person pulling block
The surface the block is being pulled across: wood, wax paper, paper towel, fine sandpaper, course sandpaper
Force of pulling measured in newtons.
Variables for Inquiry 6.2
Controlled Variables
Manipulated Variable
Responding Variable
Variables for Inquiry 6.3
Controlled Variables
Manipulated Variable
Responding Variable
- In the final reflection questions students are asked to summarize
what they have learned about the force of friction during the three
inquires. A writing strategy to help them organize their thinking
could include a claims and evidence chart for each of the three
lessons. The following chart is an example:
Claims:
Evidence:
Inquiry 6.1 (what were the overall results)
Students place evidence here…
Inquiry 6.2…
Inquiry 6.3…
Reading Support:
- There are two reading selections that follow the inquiry that
illustrate the benefits of friction.
- Nature Puts on the Brakes outlines the nature of air friction and terminal velocity.
- Rock Climbing: Two People, One Powerful Force explains how friction assists rock climbers.
Math Support:
- Students will be keep track of data, average trials and construct graphs for each of the three inquires.
- Students could calculate the surface area of the block sliding across different surfaces in Inquiry 6.3 and compare that to the surface area of the blocks they used during Inquiry 6.1 and 6.2.
- Slight differences in data for Inquiry 6.3 may arise. These small differences may lead some students to the wrong conclusion. Consider graphing the results to show the relationship of the differences in force.
- Consider calculating the coefficient of friction with the block on its side and flat, making predictions and observations.