Momentum and Inertia

1. Momentum and Inertia

2. Momentum • Momentum = mass x velocity MV = P • 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)

3. Momentum • 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

4. 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.

5. Impulse-Momentum relationship F∆t = mv • This relationship helps us to analyze situations where the p changes.

6. Bouncing • 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.

7. Conservation of Momentum • If you wish to change p, you must exert an impulse on it. • 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.

8. Conservation of Momentum • 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.

9. 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

10. Elastic Collisions • Elastic collision: • 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).

11. 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