Collisions
How does the momentum of the system before the collision compare to the momentum
of the system after the collision?
Motion
Detector
Motion
Detector
Collisions
Elastic Collision – a collision during which kinetic energy is conserved.
In other words, no energy is dissipated during the collision.
Using the magnet ends…
Motion
Detector
Motion
Detector
Collisions
Inelastic Collision – a collision during which kinetic energy is not conserved.
Some of the energy is dissipated and is usually stored as
thermal energy or sound.
Using the Velcro ends…
Motion
Detector
Motion
Detector
Collisions Post-Lab
  kgm 
Pi 

s

The Law of Conservation of Momentum
In any closed, isolated system the total
momentum remains constant

Pf
  
Pi  P1fPf
 kgm 
s

Since the graph is linear
and contains (0,0)
 
Pi  Pf
Proof
2 methods
Method 1


FBR   FRB
Method 2
Newton’s
Third Law!
t BR  t RB
RB


FBR t   FRB t


J BR   J RB


p1  p2

PTotal  0
 dp
F 
dt
Newton’s Second Law
The system is isolated and by Newton’s
Third Law, any force between colliding
objects would always have an equal and
opposite pair and would therefore sum to 0!

dp
0
dt

p  constant