Mechanics Definitions - Edexcel Physics A-level

Centre of Mass

The average point of all parts of an object weighted according to their mass.

Conservation of Momentum

In a closed system with no external forces, the momentum of the system before an event is equal to the momentum of the system after the event.

Drag

The resistance against the motion of an object through a fluid.

Moment

The product of a force and the perpendicular distance from the line of action to the pivot about which the force is acting.

Terminal Velocity

When frictional forces and driving forces are balanced and so no acceleration occurs and the resultant force on the object is 0 N.

Lift

A force acting perpendicular to the flow of air or liquid around an object.

Projectile

Any object that is thrown, launched, or falls through the air.

Newton’s First Law

An object at a constant velocity will remain at a constant velocity unless acted on by a resultant force.

Newton’s Second Law

If an object is acted upon by a resultant force it will accelerate. The acceleration is inversely proportional to the mass of the object and directly proportional to the force acting upon it.

Newton’s Third Law

Every action has an equal and opposite reaction.