Physics 100 – Conservation of Linear Momentum
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SAN DIEGO MESA COLLEGE
PHYSICS 100 LAB REPORT
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TITLE: Conservation of Linear Momentum
(Inelastic Collisions)
Objective:
To demonstrate conservation of linear momentum for completely inelastic collisions.
Theory:
Consider the situation in which a mass m1 , moving with velocity vi , collides with a
stationary mass m2 , and the two then move as a single mass m1 + m2 , with velocity vf
afterwards. The momentum before and after are given by:
initial momentum:
final momentum:
Pi = m1vi
Pf = (m1 + m2)vf
Respectively, the conservation of momentum states:
Pi = Pf
Equipment:
Air Track
2 Photogates
“needle”attachment
“flag “attachment
12” Ruler
Setup:
Revised by Dr. Goldstein on 11-‘02
Blower with hose
2 Gliders
“wax” attachment
50g Masses
White Bubble Level
Physics 100 – Conservation of Linear Momentum
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Procedure:
Refer to the diagram.
Set up an air-track and level it.
Position 2 photogates along the track (see figure 1).
Insert the “needle” attachment in one glider and the “wax” attachment in the other.
Insert the “flag” attachment on the top of the moving glider.
Measure and record the length of the flag, L.
Record the mass of the moving glider as m1 and the mass of the other glider as m2.
Place the moving glider near one end of the track, before the first photogate.
Place the other glider somewhere between the two photogates.
Give the moving glider a push.
After the gliders collide, become stuck, and pass through the second photogate, stop them before
they rebound.
Record the times from the two photogates, and call them t1 and t2 respectively.
Repeat the above steps by giving the moving glider a lighter or harder push (not too hard though).
Then repeat the procedure with different choices of m1 and m2 by placing additional weights on
the sides of the gliders. Always add two weights to a glider, one on either side for balance. And
change the weights on both gliders (don’t just add weights to one glider or the other).
CALCULATIONS
The velocity of the glider can be calculated from the time it takes the flag of the glider to pass
through the photo gate.
v = L flag / t = L/ t
Since m 2 is originally at rest,
p i i = m1v i
and
v i = L/ t 1
After the collision both masses have the same velocity. Thus,
p f = (m 1 + m 2 ) v f
and
v f = L/ t 2
Revised by Dr. Goldstein on 11-‘02
Physics 100 – Conservation of Linear Momentum
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Do sample calculations of V I , V F , P I , and P F in the space below for case 1.
Data:
.
Case
m1
kg
m2
kg
t1
s
t2
s
vi
m/s
Analysis:
Is momentum conserved within experimental errors?
Revised by Dr. Goldstein on 11-‘02
vf
m/s
Pi
kg-m/s
%
Pf
difference
kg-m/s
Physics 100 – Conservation of Linear Momentum
Conclusions:
Revised by Dr. Goldstein on 11-‘02
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