WJEC AS Physics Unit 1.3 - Dynamics

Force

Force

A force on a body is a push or a pull acting on the body from some external body

Newton’s Third Law

If Body A exerts a force on Body B, then Body B exerts an equal and opposite force on Body A

F=ma

• The mass of a body x its acceleration is equal to the vector sum of the forces acting on the body

• This vector sum is called the resultant force

Momentum

• Momentum of an object is its mass multiplied by its velocity

• p=mv

• Vector

• Unit; Ns or kgms^-1

The principle of conservation of momentum

• The vector sum of the moments of bodies in a system stays constant even if forces act between the bodies, provided there is no external resultant force

Elastic collision

A collision in which there is no change in total kinetic energy

Inelastic collision

A collision in which kinetic energy is lost

Momentum-time graphs

• gradient = Force

• Flat = constant momentum, no net force acting. Travelling at a constant speed. In equilibrium

• Negative gradient = negative force

• Curve; draw a tangent and calculate gradient for force

• Maximum force = gradient of the steepest part of the graph