Friction: Investigation 4 –
This Investigation is designed to:
- demonstrate to you that the frictional force between an object and a surface depends on the smoothness of the combination of surfaces,
- encourage you to calculate the coefficient of friction between two surfaces, and
- use graphs to illustrate the relationships between frictional force and the coefficient of friction between surfaces
Student Preparation for the Investigation includes having students gather the following materials. This preparation takes place on lab day after student groups have settled at their assigned lab tables.
Note: The materials are listed in students’ SDRs. They are also listed below for your reference.
- (1) 5 N spring scale
- (1) woodblock with hook
- (1) meter stick
- (1) roll of masking tape
- (1) penny per student
Note: The following materials should be available at the distribution center:
- (10) 11.5 x 27.9 cm pieces of sandpaper
- (5) 14 x 17 cm pieces of sandpaper
- (1) roll of wax paper
- (1) roll of aluminum foil
Note: If students were unable to leave their pieces of tape on the table, instruct them to set up their lab table as in Investigation One through Three, using four pieces of tape to create a starting line and a finish line. The lines should be 50 cm apart.
Direct one student from each lab group to collect the materials listed in their SDRs.
- The variable you will investigate is the smoothness of surfaces.
- Before beginning the experiment, identify the independent and the dependent variable in this experiment.
- Your group will investigate three combinations of surfaces. Look at Table A of your Investigation 4 Student Data Record. The table outlines all of the possible combinations of surfaces they may investigate. All students must measure the frictional force of the woodblock against the table, the first combination listed and marked with a star. Then you must choose two additional combinations to explore.
- During the Experiment, every procedural step is important. If one step is skipped, data can become invalid. To help you keep on track, read each step thoroughly, complete the step, then check it off (Read it – Do it – Check it).
- Reflect on the PreLab video as you move through the procedural steps.
- Complete all of the procedural steps in your SDR.
Note: The procedural steps are listed below for your reference.
- Arrange four pieces of tape on your table so that you have a starting line and a finish line 50 cm apart.
- In this Investigation, you will alter the surface of the woodblock and the table so that each becomes either more or less smooth.
- You will investigate a total of three combinations.
- Look at Table A. Decide which combinations you would like to investigate.
- Everyone will investigate the first combination marked with a star.
- Mark a star beside two other combinations you would like to investigate.
- To alter the surface of the woodblock (Figure 8-a):
- Wrap a piece of sandpaper, wax paper, or aluminum foil around the bottom of the block.
- Tape the paper or foil to the block.
- To alter the surface of the table (Figure 8-b):
- If using sandpaper, wax paper, or aluminum foil, spread it on the table so that it covers the table from 20 cm before the starting line to 20 cm after the finish line.
- Tape the edges of the paper or foil to the table.
Note: The piece of wax paper or foil that you lay on the table should cover the table from 20 cm before the starting line to 20 cm after the finish line. These pieces can be the width of the roll. If using sandpaper, you will need two long pieces (11.5 cm x 27.9 cm) By placing the two pieces end to end, they will be able to cover approximately 55 cm of the bench. Although this does not provide the 50 cm length of the bench that the aluminum foil and the wax paper provide, you should nonetheless be able to obtain an accurate measurement of frictional force by reading the spring scale throughout the distance pulled and calculating an approximate average force.
- If using gravel, spread it on the table so that it covers the same area as the paper and foil.
Note: You should spread gravel from 20 cm before the starting line to 20 cm after the finish line, just as with the paper or foil.
- Obtain the materials from the distribution center.
- Perform each trial:
- Measure the frictional force between the two surfaces using the spring scale.
- Measure the mass of the woodblock using the triple beam balance.
Note: The mass of the woodblock may vary as you wrap it with aluminum foil, wax paper, or sandpaper.
Record: Write the frictional force and mass for each trial in Table B.
Note: If one group completes the tasks earlier than the rest of the groups, the group that worked more quickly may wish to perform another trial with another surface combination.
Let students know your expectations for clean up. Ask them to clean up.