The Physics Factbook™
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
topic index | author index | special index
Friction is the force between two surfaces in contact that opposes motion or intended motion. Friction can be found by using
f = µFn
where µ is the coefficient of friction and N is the normal force.
In order to calculate the static coefficient of friction (µs), the angle of an inclined plane was increased gradually until the object first begins to slide downward. At that angle, the weight of the object (Fg) would have succeeded in overcoming the force of static friction (fs). Using trigonometry, it can be shown that …
fs = Fg sin θ
until the time when the object begins to slip. Therefore …
µsFn = Fg sin θ
The normal force (Fn) that the object exerts on the plane surface is equivalent to the weight of the object perpendicular to the plane …
Fn = Fg cos θ
Substituting into the previous equation will produce a new equation …
µs = tan θ
helpful for determining the coefficient of static friction, with the angle of the inclined plane being an important component.
Procedure:
LoggerPro determined the acceleration due to gravity parallel to the ramp. Using trigonometry we can determine the angle of inclination …
sin θ = gparallel / g
θ = sin-1 (gparallel / g)
| Material | gparallel (m/s2) | θ (°) | µstatic |
|---|---|---|---|
| Plastic | 3.67 | 21.9 | 0.40 |
| Cardboard | 3.9 | 23.45 | 0.43 |
| Leather | 6.75 | 43.53 | 0.95 |
| Copper | 4.84 | 29.59 | 0.57 |
Leo Tam, Jenny Hua, Stephanie Ma -- 2005
Students Choice pages in The Physics Factbook™ for 2005
| Another quality webpage by Glenn Elert |
 |
home | contact bent | chaos | eworld | facts | physics |
