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:

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. Record this angle in the coefficient of static friction table provided below. Repeat this measurement three times and take the average of your measured values. Please see the video below for extra guidance if needed.

Helpful hint: By placing an object under the ramp, you can adjust the angle by either sliding the object or sliding the ramp itself.

In the lab:


At home:

Note: If you would like to view this video in full screen, you can click on the McMaster logo found in the bottom right corner (this opens the video in a new tab).

Be sure to leave the coefficient of static friction (𝝁s) column blank for now, as you will be calculating it in the next section.

Results:

Coefficient of Static Friction Data

A 5 by 3 table. The headings of each column read trial number, angle of ramp, otherwise known as theta, which measured in degrees, and finally, coefficient of static friction, otherwise known as mu s, which is dimensionless. The first column, under trial number, reads 1, 2, 3, and then average. The remaining cells are intentionally left blank to be filled in as an exercise.

The link to download the Excel file that you may use for Lab 2 (for Exercise 2 and Exercise 3) is found below. The first tab includes the table for Exercise 2 (seen above), while the second tab has the table you will be using for Exercise 3.

Lab 2 Excel Chart Download

Analysis

Your shoe remains motionless due to friction until the angle is great enough such that the maximum 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.

Helpful hint: Remember that the normal force in this experiment is related the gravitational force, but these forces are not equal here.

Exercise 2.1 (3 marks)

Submit your completed chart from above. Please do not submit a photo of your screen taken by a separate device. Upload to Crowdmark using any of the formats shown in the Excel Help tab.

Exercise 2.2 (2 marks)

Right before your shoe starts sliding, θ reaches a maximum, meaning 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. Thus, 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. Helpful hint: Is fstatic = 𝝁sFN true at all times? Or should you reconsider the equal sign? Other options include >, <, ≤, and ≥. Pick the correct option(s) directly on Crowdmark.

Think about it:

Does your calculated coefficient of friction make sense to you?

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.