PASCO ME-9430, Инструкция по эксплуатации и руководство по экспериментам, Страница: 9 / 30

012-04840E
Dynamics Cart
5
®
Experiment 2: Coefficient of Friction
Figure 2.1
a
1
= + gsin
θ
– µ
r
g (EQN-1) (since cos
θ
= 1)
a
2
= – gsin
θ
– µ
r
g (EQN-2)
t 2
2d
a = (EQN-3)
EQUIPMENT NEEDED:
– Dynamics Cart (ME-9430)
– Metric tape (SE-8712)
– Stopwatch (SE-8702)
Purpose
In this lab, the Dynamics 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
θ,
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 down-slope, the acceleration of the cart is given by:
And the acceleration in the direction that is slightly up-slope 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:
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Having obtained numerical values for
a
1
and
a
2
,
EQN-1
and
EQN-2
can be solved
simultaneously for µ
r
and
θ
.