# What Is the Law of Conservation of Momentum?

The law of conservation of momentum says that the momentum before an event must be the same as the amount after due to its constant conservation. It is an element of the law of inertia.

Exploring Momentum
Momentum is an object's mass multiplied by its velocity. This is expressed in a formula that reads p = mv. It has both direction and magnitude, making it a vector quantity.

Law of Conservation of Momentum Examples
One example would be a vehicle accident. Two vehicles crash into each other, and their momentum is the same before and after the crash. This is determined by measuring the individual vehicle's velocity and mass. The velocities may change, but the momentum will be exactly equal.

The law of conservation of momentum is also demonstrated in a game of football. When two players run into each other, it is their momentum that determines which ones gets tackled, and not their mass. This is based on Newton's third law of motion.

Newton's First Law
Newton's first law is the law of inertia. When an object is resting, it will stay this way until an unbalanced force acts upon it. Likewise, unless an unbalanced force occurs, when an object is in motion, it will stay that way and maintain its speed.

A skateboarder is a good example. The skateboarder is moving along at a consistent speed. Unless something gets in the way (referred to as the unbalanced force), the skateboarder will keep going until he stops. Now, if there is a rock in the road and the skateboard hits it, it stops the board, and the skateboarder either stops or can fall off the board. In this scenario, the rock is the unbalanced force.

Newton's Second Law of Motion
This law says that when a force acts on a mass, acceleration is produced. As the mass of the object being accelerated increases, the force needed to accelerate it must also increase. Basically, the heavier the object, the more force that is needed to make it move. Force is determined by the formula F = MA, or force equals mass multiplied by acceleration.

For example, if two cars of unequal weight need to be pushed one mile, the heavier vehicle will require more force to get it to move. The formula for force allows someone to determine the amount of force needed to move both vehicles based on their mass and the acceleration being used.

Newton's Third Law of Motion
This law says that every action that occurs has an opposite and equal reaction. Every time an action happens, a reaction force occurs that is in the opposite direction, but equal in size. For example, an object is pushing another object. Using this law, it shows that with equal force, the object is pushed in the opposite direction by the other object.

A rocket is a good example of this law. In order for a rocket to take off, it has to push down on the ground. The engines of the rocket provide a powerful force focused on the ground. The ground pushes the rocket up as the opposite reaction using an equal force.

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