Exercise 2: Measuring coefficient of static friction

In Exercise 1, you considered a shoe at rest on a ramp. You will now be performing this experiment to determine the coefficient of static friction between the shoe and the surface it is resting on.

 

Procedure:

(see below video for extra guidance if needed)

Set up your experiment by placing your shoe (or calculator) on a flat surface that can be tilted to create a ramp/inclined plane. If you are in the lab, make sure your object is in front of the red line.

Slowly increase the angle of your ramp until the shoe begins to slide. Write down the angle of the ramp when your shoe begins to slide and record it in the coefficient of static friction table below. Repeat this measurement three times and take the average of your measured values.

In the lab:


At home:

Note: Leave the coefficient of static friction (𝝁s) column blank for now, you will be calculating it in the next section.

 

Results:

Coefficient of Static Friction Data (excel file download)

Angle of ramp

Coefficient of static friction

Trial #
θ

[°]

𝝁s

[unitless]

1

2

3

Average

 

Analysis

Your shoe remains motionless due to friction until the angle is great enough such that the max force of static friction is smaller in magnitude compared to the force of gravity parallel to the ramp. In Exercise 1, you wrote an equation for the net force acting on your shoe in this scenario where it is motionless and just on the verge of slipping.

Rearrange this equation so that you can calculate the coefficient of static friction, 𝝁s, as a function of θ (i.e. 𝝁s is on the left-hand side of the equation and everything else including θ is on the right-hand side). Use this equation to fill in the rest of the above chart with your calculated values of μs.

Exercise 2.1 (3 marks)

Submit your completed chart from above (chart template). 

Exercise 2.2 (2 marks)

Right before your shoe starts sliding, θ reaches a maximum which means the force of gravity down the ramp is also at a maximum. This force is balanced by the static friction acting up the ramp. By reducing the angle of the ramp by a factor of 2, μs does not change, yet the object remains stationary. As the angle of the ramp decreases, the normal force increases. Explain why your object remains stationary in a few short sentences.

Exercise 2.3 (1 mark)

Alter your equation (fstatic = 𝝁s FN) to reflect this. Hint: Is fstatic = 𝝁s FN true at all times? Or should you reconsider the equal sign? Other options include >, <, ≤, and ≥. Pick the correct option directly on Crowdmark.

Before you continue!

Before continuing, be sure you have completed Exercises 2.1, 2.2, and 2.3 which will be graded and submitted through Crowdmark.

 

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Physics 1A03 - Laboratory Experiments Copyright © by Physics 1A03 Team is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, except where otherwise noted.