PASCO ME-6950 PAScar with Mass - Manual (Page 6)

012-07361B PAScar with Mass
5
Experiment 2: Coefficient of Friction
Figure 2.1
a
1
= + gsin
θ – µ
r
g (since cos 2
θ + sin
2
θ =1)
a
2
= – gsin
θ – µ
r
g
a =
EQUIPMENT NEEDED:
– PAScar (ME-6950)
– Metric tape (SE-8712)
– Stopwatch (SE-8702)
Purpose
In this lab, the PAScar will be launched over the floor using the on-board spring
launcher. The car 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
θ, the small angle at which the floor is inclined, two separate experi-
ments must be done. (Recall that to determine the value of two unknowns, you must
have two equations.)
DOWNSLOPE UPSLOPE
t 2
2 d
(EQN-1):
(EQN-2):
(EQN-3):
Having obtained numerical values for a
1
and a
2
, EQN-1 and EQN-2 can be simultaneously solved
for µ
r
and
θ.
Numerical values for these accelerations can be determined by measuring both the
distance d that the car rolls before stopping and the corresponding time t. Given these
values, the acceleration can be determined from:
Theory
The car 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 car is given by:
And the acceleration in the direction that is slightly upslope will be: