Foundations of Physics
Workshop: The Momentum Collider
The Momentum
Collider
CPO Science
Key Questions
 What is Momentum?
 What are some useful properties of
momentum?
 How can we measure and observe
momentum?
 What role does momentum play in
collisions and how can we use it for
calculations?
What is Momentum?
 Property of moving matter
 Like mass, it measures an object’s resistance to
a change in speed or direction
 The product of an object’s mass and velocity
 IMPORTANT – Remember velocity is a vector so
DIRECTION is very important
Setting up the Collider
 Allows us to measure and
observe momentum
 The collider is level and
plumb
 This ensures the projectile
and target will collide
squarely
 Practice releasing the
projectile a few times
Two Objects
 Loop the String of the Target over the
post on the side of the hanger
 Take a few practice swings with the
projectile to get a feel for the release
Measure the Projectile’s Velocity
 Loop the String of the Target over the post on
the side of the hanger
 Only the projectile will be swung
 Swing the projectile through the photogates
once, then catch it so it does not swing back
through
 Calculate the velocity of the projectile; the
diameter of the projectile is 2.50 cm
 Velocity is a vector!! It is direction
sensitive!
Collect Data
 Use the CPO Data Collector and
photogates to see how long it
takes the marble to break the light
beam at points A and B
 Calculate speeds
Investigate Motion of
Projectile
 How would you calculate the
velocity?
0
What about MASS?
 Don’t we need MASS to calculate
momentum?
 We will calculate the mass of the
target from our measurements of
velocities and the mass of the
projectile at the end
 How? We will use a
“conservative” approach
Conservation of Momentum
 Like energy, momentum obeys a
conservation law
 After the collision both balls may
be moving with different speeds
and in different directions
 the total momentum after the
collision must be equal to the
total momentum before the
collision
 mpv0 = mtvt + mpvp
Different Kinds of Collisions
 In an elastic collision, the objects bounce
off of each other with no loss in the total
kinetic energy.
 In an inelastic collision, objects may
change shape, stick together, or ‘lose’
some kinetic energy to heat, sound, or
friction.
 Momentum is conserved in both elastic
and inelastic collisions, even when kinetic
energy is not conserved.
Two Objects…Again
 This time we will use both objects to
perform a collision (target diam. 3.175 cm)
 Double check to make sure they are aligned
 Predict with your group – Elastic or
Inelastic?
Performing A Collision
 Allows us to
measure and
observe momentum
 The collider is level
and plumb
 This ensures the
projectile and target
will collide squarely
Observations
 The projectile collided with the target
 The projectile actually bounced
backward in the opposite direction!
 The target swung in the same direction
as the projectile, even though the
projectile “bounced off” it
 Try it again but this time, record data
Calculate the Three Velocities
 1st velocity– the velocity of the projectile
as it approaches the collision vo
 2nd velocity– the velocity of the
projectile as it bounces back vp
 3rd velocity – the velocity of the target
after the collision vt
Using Conservation of
Momentum
 the total momentum after the collision must
be equal to the total momentum before the
collision. Insert velocity values in cm/sec
 mpv0 = mtvt + mpvp
Conservation of Momentum
 mp113.9 = mt74.5 + mp-32.3
 mp113.9 = mt74.5 - mp32.3
 Don’t Forget About Direction!
 mp146.2 = mt74.5
mp146.2 = mt74.5
 Divide both sides by 74.5
 mp146.2/74.5 = mt
 mp1.96 = mt
 If the projectile ball has a mass of
67.2 g, what is the mass of the target
ball?
We have used Momentum
 We calculated the ratio of the masses
involved in the collision
 We used the Conservation of
Momentum Equation to do it
 What would happen if they were the
same mass?
 What are other ways you can think of to
use this equation?