An Oscillating System with Sliding Friction

Both harmonic oscillations and friction are the types of concepts in freshman physics that are readily applicable to the “real world” and as such, most students find these ideas interesting. Damped oscillations are usually presented with resistance proportional to velocity, which has the advantage of a relatively straightforward mathematical solution. This type of resistance occurs for very slow moving bodies in fluid, although a more common resistive force in fluid is proportional to velocity squared.¹ Thus, mechanical oscillations with damping proportional to velocity may be more useful in the freshman course as an analogy for the future study of LRC circuits.² Whereas an oscillator with damping proportional to velocity has an exponential decay in amplitude, a system with sliding friction results in amplitude that decays in a linear manner.³ In this paper I present a demonstration of an oscillator with sliding friction that exhibits very good agreement with a linear fall off in amplitude. The demonstration also confirms that sliding friction is proportional to the magnitude of the normal force.