Physics 4AL
Lab for Science and Engineering Mechanics
Experiment 4:
Momentum and Impulse
Lab Section:
LAB 5
Name:
SunYi Lim
UID:
503576474
Date:
7/15/10
TA:
Chris Tyndall
Partner:
Jaimie Yap
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Introduction
In this experiment, we will calculate the momentum and impulse for a system composed of a ‘frictionfree’
track, a photogate, a glider with bumpers and measuring block, and a force transducer. It is normally thought that the
Newton’s second law is:
=
F
ma
However, this equation only applies to singlepoint masses. By using a more general expression of the second law,
we will be able to calculate the change of momentum and the impulse of our system. The general equation is:
=
F
dPdt
where F is the force and P is momentum. For this experiment, we will be using the differentiated form of the above
equation.
First, the force transducer will be calibrated by using different hanging masses to determine the voltage to
force conversion factor α. Then, we will record collision data between the glider and the force transducer. These
time intervals should be recorded for 5 different speeds, with 5 runs per lab partner (using different type of
bumpers). Next, we will calculate magnitudes of the velocities and momentum before and after the collision, as well
as the change in momentum using excel. Voltage correction is to be corrected in order to calculate the impulse of the
system.
Theory & Equations
As stated in the introduction, the general form of the Newton’s second law can be described as below:
=
F
dPdt
Another way of writing this equation is to use a differential equation. If we integrate with respect to time
to express the change in momentum:

=
P1P2 Fdt
Where, the right hand side is known as the impulse, and the left side is the change in momentum. The
notion of impulse is associated with a force that acts for a very short time. In this experiment, the force
transducer allows us to measure F(t) at closely spaced time intervals, compared with the time over which the
force is different from zero. Science Workshop records the numbers, which enables us to numerically integrate
as a Riemann sum. To test the impulse equation we will need to measure the vector change in momentum from
before to after the interval in which F(t) ≠ 0.
The magnitudes of the velocities and momenta before and after collision can be calculated using the
time t1 and t2 from Science Workshop by using following equations:
=
v2
Lt2
=
v1
Lt1
=
P1
Mv1
=
P2
Mv2
Where t1 is the time obtained when the block enters the photogate first time, and t2 is the time when the block
bounces back. M here is the weight of the glider, which should be measured in the beginning.
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 Summer '10
 SLATER
 Momentum, Observational error, Force Transducer

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