Momentum and Inertia Momentum n Momentum mass x

Momentum and Inertia

Momentum n Momentum = mass x velocity MV = P Momentum is inertia in motion. n A moving object has more p than an object with less m. n An object at rest has no p (v = 0) n

Momentum If the p of an object changes, the m, v, or both MUST change. n If the v changes, then the object is accelerating n a produces F n The greater the F, the greater the change in v n

Impulse The F sustained for a longer period of time produces more ∆p. n This relationship of F to t is called impulse. n Impulse = F∆t n The greater the impulse, the greater the ∆p.

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

Bouncing When an object bounces off a surface, the impulse is greater. n 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. n

Conservation of Momentum n If you wish to change p, you must exert an impulse on it. n n The impulse must be exert on the object by something outside the object. When a cannon is fired, according to Newton’s 3 rd, the ball has an equal but opposite force to the cannon. n 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 Remember p is vector quantity (magnitude AND direction) n If no net force or net impulse act on a system, the momentum of that system cannot be changed. n Law of Conservation of Momentum n n In the absence of an external force, the momentum of a system remains unchanged.

Collisions n The collision of objects clearly shows the conservation of p. Net momentum before collision = Net momentum after collision n Two main types of collisions n Elastic and inelastic

Elastic Collisions n Elastic collision: n When objects collide without being permanently deformed or without generating heat. Ex: billiard balls (pool); swinging balls apparatus n The momentum from the first object is transferred to the second object (or vice versa). n

Inelastic Collisions Inelastic collisions: n When colliding objects become entangled or coupled together, thereby generating heat or disfigurement. n The net p before the collision equals the net p after the collision n Net (mv) before collision = Net (mv) after collision