Course and Section_______ Names ___________________________
Date___________ _________________________________
COEFFICIENT OF FRICTION EXPERIMENT
In this lab you will measure the coefficient of kinetic friction between a wooden block and
the table and examine some of the factors that may affect its value. The coefficient of
kinetic friction is defined as the ratio of the frictional force to the normal force while the
block is sliding,
n
f
kF
F
=
µ
. (1)
Similarly, the coefficient of static friction is defined as the ratio of the maximum frictional
force that resists motion to the normal force,
n
f
sF
Fmax,
=
µ
(2)
We can easily measure
µ
k by measuring the horizontal force required to keep an object of a
known weight moving at constant velocity on a flat surface. For a horizontal pull, Fn is just
the weight of the object.
Preliminary questions:
Question 1:
According to your textbook, how do
µ
k and
µ
s usually compare in value? (Which is
typically larger?)
Question 2:
How do you expect the coefficient of friction to depend on the normal force? For example,
do you expect
µ
k to increase, decrease, or remain constant as the normal force is increased?
Question 3:
How do you expect
µ
k to depend on the contact area between the two sliding surfaces?
Experiment:
Place a mass of a 0.2 kg on the block. .
First, place the wooden block on the table with the largest area felt side facing down.
Attach the force sensor to the block with a string. Make sure to press the tare button on the
side of the force sensor before you take each single measurement. Set the sample rate of the
force sensor on Data Studio to 50. Use Data Studio to look at the force as a function of
time. Gradually pull until the block starts moving and then continue pulling to keep the
block moving at a constant speed (so that the force due to friction is equal the force you
applied throughout the all process. Use the motion sensor to read the velocity of the block
and check that its motion is at constant speed). Do this carefully enough to see how the
