Unit 3: Principles of Mechanical Engineering
LO5: Understand principles of dynamic systems
Coefficient of friction/limiting friction
Learner activity sheet
Activity 1
In this activity you will be conducting experiments to find the static coefficient of friction between two
surfaces.
Look at the slide and pulley arrangement and draw a force diagram for the block resting on the slide.
You will be using the limiting friction equation F = µN.
Version 1
Activity 2
Slowly and gently add weights until the block just begins to move. Record the weight of the block and the
tension in the string needed to move it. Plot these readings on a graph (Tension in the string on the y
axis, weight of the block on the x axis).
Add some weight to the block and repeat the experiment. Repeat this a sufficient number of times until
the relationship between the two values becomes clear from the graph.
Use the graph to calculate the coefficient of friction between the block and the slide.
Activity 3
By attaching samples of materials to the surfaces of the slide and the block it is possible to find the
coefficient of friction between different materials. Use double-sided sticky tape (or another suitable
method) attach samples of different materials to the base of the block and/or the surface of the slide.
Repeat the experiment in Task 2 to find the new coefficient of friction.
What are the smallest and largest values for µ that you can find?
Activity 4
How does placing the slide at an angle to the horizontal affect the experiment?
Repeat Activity 1 and Activity 2 with the slide fixed at an angle of 20o to the horizontal. You will need to
draw a new force diagram. Can you verify the result you previously obtained for the coefficient of friction
between the block and the plane?
Version 1