Momentum and
Inertia
Momentum

Momentum = mass x velocity
MV = P
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Momentum is inertia in motion.
A moving object has more p than an object
with less m.
An object at rest has no p (v = 0)
Momentum

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If the p of an object changes, the m, v, or
both MUST change.
If the v changes, then the object is
accelerating
a produces F
The greater the F, the greater the change in
v
Impulse


The F sustained for a longer period of time
produces more ∆p.
This relationship of F to t is called impulse.
Impulse = F∆t

The greater the impulse, the greater the ∆p.
Impulse-Momentum relationship
F∆t = mv

This relationship helps us to analyze
situations where the p changes.
Bouncing

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When an object bounces off a surface, the
impulse is greater.
The impulse required to bring an object to a
stop and then to throw it back again is
greater than the impulse required merely to
bring it to a stop.
Conservation of Momentum

If you wish to change p, you must exert an
impulse on it.

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The impulse must be exert on the object by
something outside the object.
When a cannon is fired, according to
Newton’s 3rd, the ball has an equal but
opposite force to the cannon.

Same thing with p (within the system of the
cannon and the ball)…the overall p before and
after do not change.
Conservation of Momentum
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Remember p is vector quantity (magnitude
AND direction)
If no net force or net impulse act on a
system, the momentum of that system
cannot be changed.
Law of Conservation of Momentum

In the absence of an external force, the
momentum of a system remains unchanged.
Collisions

The collision of objects clearly shows the
conservation of p.
Net momentum before collision =
Net momentum after collision

Two main types of collisions

Elastic and inelastic
Elastic Collisions

Elastic collision:

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When objects collide without being permanently
deformed or without generating heat.
Ex: billiard balls (pool); swinging balls
apparatus
The momentum from the first object is
transferred to the second object (or vice
versa).
Inelastic Collisions
Inelastic collisions:
 When colliding objects become
entangled or coupled together, thereby
generating heat or disfigurement.
 The net p before the collision equals the
net p after the collision

Net (mv) before collision = Net (mv) after collision