Experiments
Plunger Cart
012-14781A
7
Experiment 2: Coefficient of Friction
Purpose
In this lab, the Plunger Cart will be launched over the floor using the on-board spring launcher. The
cart will “decelerate” over the floor under the combined action of rolling friction and the average
floor slope. To determine both the coefficient of rolling friction µ
r
and
, the small angle at which the
floor is inclined, two separate experiments must be done. (Recall that to determine the value of two
unknowns, you must have two equations.)
Theory
The cart will be launched several times in one direction, and then it will be launched several times
along the same course, but in the opposite direction. For example, if the first few runs are toward
the east, then the next few runs will be toward the west. See Figure 2.1. In the direction which is
slightly downslope, the acceleration of the Plunger Cart is given by the following equation:
And the acceleration in the direction that is slightly upslope will be:
Numerical values for these accelerations can be determined by measuring both the distance d that
the cart rolls before stopping and the corresponding time t. Given these values, the acceleration
can be determined from the following equation:
Having obtained numerical values for a
1
and a
2
, Eqn. 1 and Eqn. 2 can be simultaneously solved
for
µ
r
and
.
Equipment Needed
Plunger Cart
Metric Tape Measure
Stopwatch
Figure 2.1
UPSLOPE
DOWNSLOPE
1
r
a
gsin
g
Eqn. 1
2
r
a
gsin
g
Eqn. 2
2
2d
a
t
Eqn. 3