Collisions
momentum and impulse
Learning outcomes

What is the linear momentum

The rate of change of momentum

The principle of conservation of momentum

Types of collision
The Newton’s 2nd law
The net force on an object is equal to its mass, times its acceleration
F net =
𝑑 (𝑚 𝑣)
𝑑𝑡
F net =m a
Linear Momentum
Momentum is VECTOR quantity that can be calculated
using the equation:
P=m V
The Unit of momentum in the SI system: kg m s-1 OR N s
Object:
Larger objects have more momentum than small objects
Faster objects have more momentum than slower objects
Impulse
Product of a force acting on an object multiplied by the time for
which it acts
The change of momentum
J= ∆ 𝑃 = 𝑚 𝑢 − 𝑣 = 𝐹 ∆ 𝑡
Impulse can be measured in kg m s-1 OR N m
The Newton’s 3rd law
When two bodies interact, the forces they exert on each other
are equal and opposite
∆𝑇
+
A
B
FB
A
B
FA = FB
VA
VB
the change of
momentum
same collision time T
𝐹𝐴 ∆𝑇 = 𝐹𝐵 ∆𝑇
∆𝑃𝐴 = − ∆𝑃𝐵
∆𝑃𝐴 + ∆𝑃𝐵 = 0
FA
The conservation of momentum
The total linear momentum of a system remains constant in
collisions / explosions provided no external force are
applied
Elastic collision
No kinetic
energy lost
Inelastic collision
Kinetic energy lost
Perfectly inelastic collision
𝑃=𝑚𝑣
𝑣
𝑃=𝑚 2
2
When two objects collide and move together as one mass, the collision is called
perfectly in elastic collision
In Collisions
 Elastic:
NO KE lost
 Inelastic:
KE lost
 Perfectly
Inelastic: stick together
The total momentum is always conserved