Contact and Non-Contact Forces — AQA GCSE Physics
A force is a push or pull on an object due to an interaction with another object. Forces are vectors.
Two categories of force
- Contact forces — the objects must be physically touching. Examples: friction, air resistance (drag), tension in a rope, and the normal contact force.
- Non-contact forces — act at a distance, without the objects touching. Examples: gravitational force, magnetic force and electrostatic force.
Force as a vector
All forces have magnitude and direction, so they are vectors and can be shown as arrows. The arrow's length represents the size of the force and the direction shows which way it acts.
Interaction pairs
When two objects interact, they exert equal and opposite forces on each other (Newton's third law). For example, the Earth pulls on you (your weight) and you pull on the Earth with an equal and opposite force.
Resultant forces
When several forces act on an object, they can be combined into a single resultant force. If the resultant is zero, the object is in equilibrium.
Exam tips
- Contact forces need touching (friction, tension, normal, air resistance).
- Non-contact forces act at a distance (gravity, magnetism, electrostatic).
- All forces are vectors — show them as arrows.
- Interacting objects exert equal and opposite forces.