Exercise 1: Planning your experiment
In this lab you will be exploring the exciting world of tribology, or, the science of friction. The goal of the following experiments is to determine the coefficient of static and kinetic friction between your shoe and an inclined surface of your choice (i.e., measure the mu of your shoe).
There are several common ways of making this type of measurement, and today you will be using the setup described in parts c) and d) of the Warm-Up Exercise. You will look at two cases:
1. when your shoe is just about to slide; any greater angle of the ramp will result in the shoe accelerating down the ramp, and
2. when your shoe accelerates at a constant rate down a ramp with an angle slightly larger than found in case 1.
Before you continue, collect the following:
- Inclined plane/ramp for which the angle can be adjusted. Suggestions: a long piece of cardboard works great to make a ramp, or a coffee table that you can tilt, a whiteboard, anything smooth and flat that can be tilted and has a length of at least 40cm, the longer it is the more accurate your measurement results.
- Protractor
- One shoe, or your McMaster standard calculator.
- Measuring tape
Scenario 1: Place your shoe on the flat surface and slowly tilt the ramp up increasing the angle.
For this scenario answer the following:
Exercise 1.1 (1 mark)
Draw the FBD for the forces that are acting on your shoe right before it starts sliding but is still stationary, and make sure you properly label the forces. Define your axes to be parallel and perpendicular to the ramp. Take the direction down the ramp to be the positive x-direction and up out of the ramp to be the positive y-direction. Pick the correct option directly on Crowdmark.
Exercise 1.2 (1 mark)
Write an equation for the sum of the forces acting on your shoe in the direction parallel to the ramp. Your equation should look like this:
[sum of all forces] = ma = _N
where [sum of all forces] is a list of all of the forces acting on your shoe in the parallel x-direction. Make sure you include the correct sign for your forces. You may wish to refer to one of the free-body diagrams in the Warm-Up Exercises. Pick the correct option directly on Crowdmark.
Scenario 2: Now review the case where angle of the ramp is large enough that the shoe accelerates down the ramp.
For this scenario answer the following:
Exercises 1.3 (1 mark)
Draw the FBD for the forces that are acting on your shoe when it is sliding down the ramp (remember that the length of the vector corresponds to the magnitude of the force)? Pick the correct option directly on Crowdmark.
Exercises 1.4 (1 mark)
Write an equation for the net force acting on your object in the horizontal direction. Your equation should look like this:
[sum of all forces] = ma
where [sum of all forces] is a list of all of the forces acting on your shoe in the horizontal direction. Pick the correct option directly on Crowdmark.
Exercises 1.5 (1 mark)
How does the equation in (1.4) differ from the equation in (1.2)? Pick the correct option directly on Crowdmark.
Before you continue!
Before continuing, be sure you have completed Exercises 1.1 – 1.5, which will be graded and submitted through Crowdmark.
