AP Physics 1 Laboratory
Coefficients of Friction; the Mu Shoe Lab
DISCUSSION:
Friction is the force that resists motion and can be determined in either static situations or kinetic
situations using the following equation:
F f  N
Static friction is the amount of friction that resists the start of motion and kinetic friction resists an
object’s continued motion. The coefficient of friction depends on a number of factors including surface
area and the types of surfaces in contact. The only way to determine a coefficient of friction is
experimentally. (Note: if a graph of Ff vs. N is draw, the slope of the graph is μ).
The angle of repose is defined as the angle at which an object just starts to slide down an inclined plane.
If θ is the angle of repose, it can be shown that μ = tan θ. We will call this method to determine the static
coefficient of friction the angle of repose method.
In this experiment you will determine the coefficient of static friction between the rubber stoppers on
your calculator and an aluminum track; you will repeat this with a shoe from someone in your lab group
on the same ramp.
THE EXPERIMENT:
1. Find the coefficient of static friction by slowly raising the incline plane until the calculator just
begins to slide. Calculate the angle. Repeat 3 times and average to accurately find the angle of
repose. Then calculate the approximate value of μ for this surface combination.
Set up a neat data table on the top of the back side of this sheet (with title, label, units, etc.)
2. Now repeat with a standard/flat soled shoe (anyone with stiletto heels?). Repeat 3 times and average
to accurately find the angle of repose. Set up another neat data table as before and repeat the μ
calculation.
ANALYSIS:
In addition to any necessary measurements or calculations from the experiment itself, include the
following on a short report you will write on the back side of this sheet.
3. Apply Newton’s 2nd Law and show that μs = tan θ on incline planes.
4. Explain what happens to the angle of repose if the mass on the incline plane is doubled.
5. What would happen to the angle of repose if someone had spilled some pop on the ramp
unknowingly the day before?