Verification of the
Principle of Conservation
of Momentum
Using a ticker timer
T.H.
The Professional Development Service for Teachers is funded by the
Department of Education and Skills under the National Development Plan
Apparatus
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The ticker tape timer
 This is connected to
12 V AC.
 It prints 50 dots per
second on a strip of
ticker tape paper.
 Each dot is printed
1/50 of a second
after the one before
it.
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Precautions
 Clean the runway
with spirits to remove
any dust or debris.
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Precautions
 Adjust the slope of
the runway until the
dots are equally
spaced when a
single trolley is given
a quick push.
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To see if you’ve compensated enough for
friction:
 give a trolley a
slight push
 and see if the dots
are equally
spaced.
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Set up the apparatus as in the photograph.
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Method
 Give Trolley A a push
and release it
immediately.
 It will collide with Trolley
B and the pins and cork
will ensure that they
stick together.
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Method
 Calculate the speed of Trolley A and the speed of
the combined trolleys from the ticker tape.
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Conservation of momentum
 In the absence of external forces:
 the total momentum before the collision
is equal to the total momentum after
the collision.
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Conservation of momentum
Momentum Before = mass A  velocity A
 m Av A
Momentum After =  mass A  mass B   velocity A+B
  mA  mB  v A B
Thus
mAvA   mA  mB  vAB
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Method
 Find the mass
of trolley A.
 Convert to standard
units.
 (Write the result
down.)
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Method
 Find the mass
of trolley B.
 Convert to standard
units.
 (Write the result
down.)
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Find the velocity of trolley A from this tape
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Answer
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Find the velocity of the combined trolleys.
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Answer
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Use these results to see if the experiment verifies
the principle of conservation of momentum.
mA  373  8 g
mB  355  2 g
 0  3738 kg
 0  3552 kg
v A  0  54 m s 1
v A B  0  28 m s 1
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Results
Momentum Before = mAv A
 0  3738  0  54
 0  202 kg m s 1
Momentum After   mA  mB  vA B
  0  3738  0  3552   0  28
 0  204 kg m s 1
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Conclusion
 The total momentum before the collision
equals the total momentum after (to two
significant figures.)
 This experiment verified the principle of
conservation of momentum to two
significant figures.
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Further Work
 Repeat the entire experiment, adding
weights to either or both trolleys.
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