A FORCE is a push or pull that acts on an object due to an interaction with another object.
Forces are VECTOR quantities — they have magnitude and direction.
Measured in NEWTONS (N).
Forces can: change speed, change direction, change shape of an object.
All forces arise from interactions between two objects:
Object A exerts a force on object B.
Object B exerts an equal and opposite force on object A (Newton's Third Law).
Contact Forces
CONTACT FORCES require the two objects to be PHYSICALLY TOUCHING.
EXAMPLES:
FRICTION — opposes relative motion between surfaces in contact. A book sliding along a table.
AIR RESISTANCE (drag) — friction between an object and air/fluid. A car moving through air.
TENSION — pulling force through a string, rope or cable. A hanging weight.
NORMAL CONTACT FORCE — perpendicular force from a surface on an object resting on it. Book on a table.
COMPRESSION — a pushing force through a solid. A compressed spring.
UPTHRUST — upward force from a fluid on a submerged object. A boat floating.
Contact forces act through direct physical interaction between surfaces.
Non-Contact Forces
NON-CONTACT FORCES act between objects that are PHYSICALLY SEPARATED — no touching required.
Three fundamental non-contact forces at GCSE:
GRAVITATION (gravity):
Attractive force between any two objects with mass.
The Earth attracts all objects towards its centre.
Acts over very large distances — the Sun's gravity holds planets in orbit.
ELECTROSTATIC FORCE:
Force between charged objects.
Opposite charges attract; like charges repel.
Example: charged balloon sticks to a wall (different charges attract).
MAGNETIC FORCE:
Force between magnets or between a magnet and a magnetic material.
Opposite poles attract; like poles repel.
Acts through space without physical contact — a magnet picks up iron filings from a distance.
All three non-contact forces can attract or repel (except gravity — gravity is always attractive).
⚠️ Common Mistake
Gravity is a NON-CONTACT force — it acts at a distance without objects touching. Weight is the gravitational force on an object. Normal contact force is NOT the same as weight — normal force is a REACTION from the surface, perpendicular to it.
📌 Key Note
Contact: friction, air resistance, tension, normal contact, compression, upthrust. Non-contact: gravity (always attractive), electrostatic (attract/repel), magnetic (attract/repel). Force = vector (N). Forces cause changes in speed, direction or shape.
🎯 Matching Activity — Contact or Non-Contact?
Sort each force into contact or non-contact. — drag the symbols on the right to match the component names on the left.
Contact force
Drop here
Contact force
Drop here
Contact force
Drop here
Non-contact force
Drop here
Non-contact force
Drop here
Gravity — attractive force between masses, acts without touching
Tension — pull through a rope or string physically attached to objects
Normal contact force — surface pushes perpendicularly on resting object
Magnetic force — acts between magnets across empty space
Friction — acts between surfaces in direct physical contact
🎯 Test Yourself
Question 1 of 2
1. A book rests on a table. Which two forces act on the book and what type are they?
2. Which of the following is a non-contact force?
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