The Weights in This Experiment Are Heavy and Can Cause Injury If Dropped. Be Careful!

FRICTION LAB

Friction is a force that opposes motion between two objects that are touching. The amount of friction depends on the types of surfaces that are in contact with each other and the force pressing the surfaces together.
In this experiment, you will examine the effect of different surface types and different weights on the amount of friction between two objects.

SAFETY

• The weights in this experiment are heavy and can cause injury if dropped. Be careful!

PROCEDURE

1. Set up the apparatus as shown. You will need to hold the large plate in place rather than using a C-clamp.
2. Place the small plate with the smooth surface down at one end of the large plate. Place a 2-kg weight on the small plate.
3. Connect the spring balance to the small plate as shown and “zero” the spring balance.
4. Gradually start to pull on the spring balance. Increase the pulling force slowly until the small plate begins to move. Then adjust the pulling force so that the small plate moves at a constant speed. Note the force required to keep the plate moving and record it in your data table. Repeat this step twice and record the force for each trial.
5. Add a 1-kg weight to the 2-kg weight for a total of 3-kg. Repeat step 4 three times and record the force for each trial.
6. Remove the weights and turn the small plate over so that the rough surface is face-down at one end of the large plate. Repeat step 4 three times using 2-kg of weight. Repeat again using 3-kg of weight. Record the force for each trial.
7. Remove the weights and spread a small amount of soap lubricant on the surface of the large plate. Use just enough to form a thin film over the plate. Distribute the lubricant evenly by moving the SMOOTH surface of the small plate over the large plate. Position the small plate with the smooth surface down at one end of the large plate.
8. Repeat step 4 three times using 2-kg of weight. Repeat again using 3-kg of weight. Record the force for each trial.
9. Carefully clean and dry the surfaces of the two plates to remove all traces of the lubricant and return your supplies to the teacher.

OBSERVATIONS

Record your observations in your lab notebook using the following data table as a guide.

VARIABLES

/ TRIAL 1 (N) / TRIAL 2 (N) / TRIAL 3 (N) / AVERAGE FORCE (N)

Smooth, 2-kg

Smooth, 3-kg
Rough, 2-kg
Rough, 3-kg
Lubricant, 2-kg
Lubricant, 3-kg

ANALYSIS

Complete the Data Table by finding the average force for each set of trials. You do not need to show your calculations.

CONCLUSIONS

Write a conclusion for this lab based on your results. Use your data to support your response to each question.

• For any given weight, how did the surface type affect the amount of friction between the two plates?
• For any given surface type, how did the weight affect the amount of friction between the two plates?
• In winter, some drivers place sand bags in their car trunks or truck beds to better cope with driving on snow-covered roads. Does this make sense according to your lab results? Explain why or why not.

Adapted from Principles of Technology, Subunit 1: Resistance in Mechanical Systems.

Friction LabIPC