Year 9 Forces

Force

A push or pull acting on an object.

Direction

The way in which a force acts or an object moves.

Magnitude

The size or strength of a force.

Force-arrow diagram

A diagram that uses arrows to show forces acting on an object.

Contact force

A force that acts when two objects touch.

Non-contact force

A force that acts without objects touching.

Friction

A force that opposes motion between surfaces in contact.

Gravity

The force that attracts objects towards Earth.

Weight

The force caused by gravity acting on an object's mass.

Net force

The overall force after all forces have been combined.

Resultant force

Another name for the net force acting on an object.

Balanced forces

Forces that are equal in size and opposite in direction, giving a net force of zero.

Unbalanced forces

Forces that do not cancel out, producing a net force.

Constant velocity

Moving at a steady speed in a straight line.

Newton's First Law

An object stays at rest or moves at constant velocity unless acted on by an unbalanced force.

Inertia

The tendency of an object to resist changes in motion.

Mass

The amount of matter in an object.

Newton's Second Law

The acceleration of an object depends on the force applied and its mass.

Acceleration

The rate at which velocity changes.

F = ma

Formula linking force, mass and acceleration.

Newton (N)

The unit used to measure force.

Newton's Third Law

When one object exerts a force on another, the second object exerts an equal and opposite force back.

Action-reaction pair

The two equal and opposite forces described by Newton's Third Law.

Interaction

When two objects affect each other by exerting forces.

Normal contact force

The support force exerted by a surface on an object in contact with it.