The 3 rd Law of Motion, Momentum and Impulse

1. The 3rd Law of Motion, Momentum and Impulse 3.1

2. Newton’s 3rd Law of Motion • Newton’s 3rd Law is about action and reaction pairs. • The 3rd Law states that every action creates a reaction that is equal and opposite. • The key to understanding this law is to understand that the action-reaction pairs do not cancel each other out. If you push on the ground on a pair of skates, you are able to move forward because the ground is able to match your force in the opposite direction.

3. Momentum • Why is it that an object with a large mass is harder to stop than an object with a smaller mass which is moving at an identical speed? • The answer is momentum. Momentum is a lot like inertia but it also includes a speed (velocity). • The formula for momentum is p = mv • Momentum is measured in kg . m/s

4. Impulse • If a force is applied to an object and the momentum is changed, this change is referred to as an impulse. • Impulse is caused by a force being in contact with an object for a period of time thereby causing a change in the object’s momentum. • Ft = mv2 – mv1 “Ft” is the part of the equation that stands for momentum, mv2 is the final momentum and mv1 is the initial momentum.

5. The Law of Conservation of Momentum • One important law to understand deals with how momentum is conserved in an action-reaction pair. • Basically the law of conservation of momentum states that a closed system (outside forces are absent) that momentum is not lost when transferred between objects. • When a cue ball “breaks” in a game of pool, the cue ball’s momentum before contact is transferred into the total momentum of all of the pool balls after contact.