# The Third Law of Motion Section 3.

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The Third Law of Motion Section 3

The Third Law of Motion For every action force, there is an equal and opposite reaction force Jumping on a trampoline cause the trampoline to exert an equal force upward The forces will always be equal but in opposite directions

The Third Law of Motion Action and Reaction forces do not cancel each other out This is because the force is equal but the force is being applied to different objects

Rocket Propulsion In aerospace engineering, the principal of action and reaction is very important. Newton's third law explains the generation of thrust by a rocket engine Hot exhaust gas is produced through the combustion of a fuel The hot exhaust gas flows through the rocket nozzle and is accelerated to the rear of the rocket In re-action, a thrusting force is produced on the engine mount.

Momentum A moving object has a property called momentum
Momentum will have the direction of the velocity Momentum can be positive or negative Momentum = mass (kg) x velocity (m/s) p = m x v

What is the momentum of a car with a mass of 1300 kg traveling at a speed of 28 m/s?

A baseball thrown by a pitcher has a momentum of 6. 0 kg m/s
A baseball thrown by a pitcher has a momentum of 6.0 kg m/s. If the baseball’s mass is 0.15 kg, what is the baseball’s speed?

What is the mass of a person walking at a speed of 0
What is the mass of a person walking at a speed of 0.8 m/s if their momentum is 52 kg m/s?

Law of Conservation of Momentum
The momentum of an object doesn’t change unless its mass, velocity or both change The total momentum of all objects in a collision will be the same before and after the collision Total momentum can’t be lost or created. Law of conservation of momentum If a group of objects exerts forces only on each other, their total momentum shouldn’t change.