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.

1.
See for instance Section 2.4 of G.R. Fowles and G.L. Cassidy, Analytical Mechanics, 6th ed. (Saunders College Publishing, 1999).
2.
Daniel
Hoyt
, “
More on damped oscillators
,”
Phys. Teach.
43
,
196
197
(April
2005
).
3.
M. I.
Molina
, “
Exponential versus linear amplitude decay in damped oscillators
,”
Phys. Teach.
42
,
485
487
(Nov.
2004
).
4.
See the following reference for another setup: C.
Barratt
and
George L.
Strobel
, “
Sliding friction and the harmonic oscillator
,”
Am. J. Phys.
49
,
500
501
(May
1981
).
5.
PASCO scientific, http://www.pasco.com.
6.
Vernier Software & Technology, www.vernier.com. Logger Pro version 3.3 was used in this demonstration.
7.
I. Richard
Lapidus
, “
Motion of a harmonic oscillator with sliding friction
,”
Am. J. Phys.
38
,
1360
1361
(Nov.
1970
).
8.
Robert. C.
Hudson
and
C. R.
Finfgeld
, “
Laplace transform solution for the oscillator damped by dry friction
,”
Am. J. Phys.
39
,
568
570
(May
1971
).
9.
The author would like to thank the referee for suggesting this approach.
10.
See for instance Section 8.8 of George Arfken, Mathematical Methods for Physicists, 3rd ed. (Academic Press, 1985); or an introductory text on ordinary differential equations.
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