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Learning Introductory Physics with Activities

Paul J. Emigh, Rebecka Tumblin, Kathryn Hadley, Danielle Skinner

Section 4.6 The Force of Kinetic Friction

Definition 4.6.1. Kinetic Friction.

The magnitude of any kinetic friction force is related to the corresponding normal force
\begin{equation*} |\vec{F}^{kf}_{12}| = \mu_k |\vec{F}^{N}_{12}| \end{equation*}
The kinetic friction will act in a direction that opposes the relative motion of the objects involved.
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The constant \(\mu_k\) is called the coefficient of kinetic friction; it is a property of the surfaces of the two objects involved in the force that is usually smaller than the corresponding \(\mu_s\text{.}\)
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Exercises Activities

1. Explaining Friction.

Give a one- or two-sentence explanation of the difference between static and kinetic friction, aimed at someone who has never taken a physics course.
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2. Exploring Coefficients of Friction.

Do a search to find a table of coefficients of friction (both static and kinetic) for different substances. What is the general range of values that you see?
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4. Describe Friction.

Describe an observation you were able to make using the simulation, especially if you observed anything that you consider unexpected or surprising.
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5. Experiment with Friction.

Design and carry out a (simple) experiment to test something using the simulation. Describe your experiment, your results, and what you feel you learned from carrying out your experiment.
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