ID:_____NAME:_________________________________________DATE:___________CLASS:______
Ch. 7 Collision Notes: 7.4 – 7.6

Law of Conservation of Momentum:
IN THE ABSENCE OF AN EXTERNAL FORCE, THE MOMENTUM OF A SYSTEM REMAINS UNCHANGED. In other
words, In the absence of outside influences, the total amount of momentum in a system is conserved.
 The momentum of the cue ball is transferred to other pool balls.
 The momentum of the pool ball (or balls) after the collision must be equal to the momentum of the cue
ball before the collision
NEWTON’S CRADLE NOTES: (write down any observations here):
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CANNONS: The momentum before firing is
zero. After firing, the net momentum is still
zero because the momentum of the cannon is
equal and opposite to the momentum of the
cannonball.
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
Velocity cannon to left is negative
Velocity of cannonball to right is positive
7.5: Collisions
Qualities
Describe how they
collide – bounce,
stick together,
etc…
Give real life
examples:
ELASTIC
INELASTIC
What happens to
the momentum
after collision? Is
it conserved? Is it
shared, or
transferred…
Are the objects
permanently
deformed postcollision?
Is heat generated
during the
collision?
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•

Go to
Elastic collisions with equal massed objects show no change in speed to conserve momentum
Elastic collisions with unequally massed objects show changes in speed to conserve momentum
– Larger mass collides with smaller mass—smaller mass object’s speed is greater than the larger
mass object
– Smaller mass object collides with larger mass object—larger mass object’s speed is much less
than the smaller mass object
Addition of mass in inelastic collisions causes the speed of the combined masses to decrease in order
for momentum to be conserved
a. A moving ball strikes a ball at
rest. Momentum of the first
ball was transferred to the
second; velocity is identical
b. Two moving balls collide headon. The momentum of each
ball was transferred to the
other; each kept same speed in
opposite direction
c. Two balls moving in the same
direction at different speeds
collide. The momentum of the
first was transferred to the
second and the momentum of
the second was transferred to
the first. Speeds to conserve
momentum.
http://www.walter-fendt.de/ph14e/collision.htm
Spend 3-5 minutes playing around with the app. After 3-5 minutes, please begin the
scenarios on the next page. You need to type into the boxes to change masses, velocities, etc. Watch for
trends! (HINT – You may want to toggle between the Velocity and Momentum options on the bottom right in order
to get accurate data AFTER collision. You have to hit “Reset” in order to start a new data trial.)
Scenario #1:
Elastic collision between wagons of equal mass, with one of the wagons initially at rest.
1. Make a hypothesis about initial and final momentums before playing with the app:
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2.
Try the app, and fill in the below chart:
Collision Type: Elastic
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Total Momentum:
3.
What is the relationship between the initial and final total momentums?
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4. Describe the motion of the wagons before and after the collision? (Was your hypothesis correct?)
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Scenario #2:
Elastic collision between wagons of unequal mass, with one of the wagons initially at rest.
5. Make a hypothesis about initial and final momentums before playing with the app:
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6.
Try the app, and fill in the below chart:
Collision Type: Elastic
BEFORE
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
7.
AFTER
Mass of Wagon 1
Total Momentum:
What is the relationship between the initial and final total momentums?
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8.
Describe the motion of the wagons before and after the collision? (Was your hypothesis correct?)
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Scenario #3:
INelastic collision between wagons of equal mass, with one of the wagons initially at rest.
9. Make a hypothesis about initial and final momentums before playing with the app:
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10.Try the app, and fill in the below chart:
Collision Type: Inelastic
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Total Momentum:
11.What is the relationship between the initial and final total momentums?
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12.Describe the motion of the wagons before and after the collision? (Was your hypothesis correct?)
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Scenario #4:
INelastic collision between wagons of unequal mass, with one of the wagons initially at
rest.
13.Make a hypothesis about initial and final momentums before playing with the app:
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14.Try the app, and fill in the below chart:
Collision Type: Inelastic
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Total Momentum:
Velocity of Wagon 2
Velocity of Wagon 1
Total Momentum:
Velocity of Wagon 2
15.What is the relationship between the initial and final total momentums?
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16.Describe the motion of the wagons before and after the collision? (Was your hypothesis correct?)
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PART 2 – Try your own if time allows! Fill out the charts below with your own data.
Collision Type:________________________ (elastic or inelastic)
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Collision Type:________________________ (elastic or inelastic)
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Collision Type:________________________ (elastic or inelastic)
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Velocity of Wagon 1
Velocity of Wagon 2
Total Momentum:
Collision Type:________________________ (elastic or inelastic)
BEFORE
AFTER
Mass of Wagon 1
Mass of Wagon 2
Mass of Wagon 1
Mass of Wagon 2
Velocity of Wagon 1
Total Momentum:
Velocity of Wagon 2
Velocity of Wagon 1
Total Momentum:
Velocity of Wagon 2
Momentum = mass x velocity
p = mv
Impulse = change in momentum
Ft =  (mv) which means that Ft = (mvf) - (mvo) OR Ft = m (vf - vo)
Additionally,
F =  (mv) which means that F = (mvf) - (mvo) OR F = m(vf - vo)
t
t
t

Whenever objects collide in the absence of external forces:
(net momentum of both objects BEFORE collision) = (net momentum of both objects AFTER collision)
(net momentum) BEFORE collision = (net momentum) AFTER collision
net (mv) i = net (mv) f
Σ (mv) i = Σ (mv) f
If there are 2 objects…
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

We will label their masses as m1 & m2
We will label their initial velocities as vi1 & vi2
We will label their final velocities as vf1 & vf2
If momentum is conserved, then:
(mass of first object
x first object’s initial velocity) +
(mass of second object
x second object’s initial velocity)
=
x
(mass of first object first object’s final velocity)
ELASTIC COLLISION EQUATION:
+
(mass of second object
x second object’s final velocity)
INELASTIC COLLISION EQUATION:
***This looks more complicated than it actually is!!! It’s very simple: read the problem, label one object as m1
with a velocity of vi1. Do the same with the other object, but call it 2. Then, AFTER COLLISION, it is no longer the
“initial” scenario…..it is the FINAL scenario. So, call them m1 with a velocity of vf1, and do the same except call it
object 2