Contact vs non-contact forces for GCSE Physics

A contact force is a force that acts between two objects that are physically touching. A non-contact force is a force that acts between two objects without them touching, through a field. Friction, tension, normal contact force, and air resistance are contact forces. Gravity, magnetism, and electrostatic force are non-contact forces.

This guide explains both types in plain English, gives the everyday examples AQA asks about, shows how to draw a force diagram correctly, and covers the exam questions students get wrong year after year. By the end you will be ready for any force-identification or free-body diagram question in Paper 2.

A contact force is a push or pull that only acts when two objects are physically in contact with each other. The moment the objects separate, the force disappears. A non-contact force is a push or pull that acts between two objects through a field, even when they are not touching.

Fields are regions of space where a force can be felt. Gravitational fields, magnetic fields, and electric fields are all non-contact field types. For GCSE Physics you do not need to model the field mathematically, but you do need to know that the field is how the force is transmitted.

Four contact forces come up regularly in GCSE Physics: Friction, air resistance (or drag), tension, and normal contact force. Each one only acts while the objects are touching.

Friction acts between surfaces that slide or try to slide past each other. Air resistance acts on objects moving through air. Tension acts in stretched ropes, cables, or springs. Normal contact force acts at right angles to a surface, pushing back on whatever is pressing on it.

Three non-contact forces feature in GCSE Physics: Gravitational force, magnetic force, and electrostatic force. Each one acts through a field, which means it can act over a distance with nothing physical between the two objects.

Gravity acts between any two objects with mass, like the Earth and the Moon. Magnetism acts between magnetic materials, like a fridge magnet and a fridge door. Electrostatic force acts between charged objects, like a rubbed balloon and your hair.

A free-body diagram shows all the forces acting on a single object. Each force is drawn as an arrow. The length of the arrow shows the size, and the direction of the arrow shows which way the force acts. The arrow must start from the object.

For a book resting on a table, the only two forces are gravity acting downwards and the normal contact force acting upwards. Both are equal in size, so the book is in equilibrium and does not move. AQA loves to ask students to draw or label this exact diagram.

Question: "A skydiver is falling at terminal velocity. Identify the forces acting on her and state whether each is a contact or non-contact force." (4 marks)

Force 1: Weight, acting downwards. This is the gravitational force on the skydiver from the Earth. It is a non-contact force.

Force 2: Air resistance, acting upwards. This is the drag force from the air pushing against her as she falls through it. It is a contact force.

At terminal velocity, weight equals air resistance, so the resultant force is zero and the skydiver falls at a steady speed. Identify both forces, label both as contact or non-contact, and you score full marks.

Force is a vector quantity, which means it has both size (magnitude) and direction. This is why force arrows must be drawn with a clear direction. Scalar quantities, like mass, energy, and temperature, only have a size.

AQA examines this distinction directly. A typical 1-mark question reads: "State one difference between a scalar and a vector quantity." The model answer is: A vector has both magnitude and direction, whereas a scalar only has magnitude. Memorise that sentence word for word.