3.13 - 3.14 Forces and Newtons laws Part 2

Newton’s First Law

A body will remain at rest or continue to move with constant velocity unless acted upon by a resultant external force.

Newton’s Second Law

The resultant force acting on an object is directly proportional to the rate of change of momentum and the change in momentum occurs in the same direction as the resultant force.

Newton’s Third Law

If body A exerts a force on body B, body B exerts a force on body A which is equal in magnitude but opposite in direction.

Two objects A and B collide. Explain, using Newton's third law of motion, the relationship between the impulse experienced by A and the impulse experienced by B during the collision.

• By Newton's 3rd Law, the force exerted on B due to A is equal in magnitude and opposite in direction to the force exerted on A due to B;

• the time of contact during the collision is the same for both objects and impulse = Ft;

• Hence, the impulse on A is equal in magnitude and opposite in direction to the impulse on B.

Linear Momentum

Linear Momentum = Mass × Velocity

Impulse

Force x time for which the force acts

Conservation of Momentum

The total momentum of a closed system is a constant (provided no external forces are applied).

Elastic Collison

A collision with no loss of kinetic energy.

Inelastic Collision

During the collision there is some loss of kinetic energy.

Explain why linear momentum is a vector quantity

The product of a scalar (mass) and a vector (velocity) is a vector (momentum).