What is a contact force?

A contact force is a force that acts between two objects that are physically touching each other.

In GCSE Physics, understanding contact forces is crucial as they are fundamental to many physical interactions. Contact forces arise from the direct physical interaction between objects. Examples include friction, tension, normal force, and applied force. When you push a book across a table, the force you exert on the book is a contact force. Similarly, the friction between the book and the table that resists its motion is also a contact force.

Friction is a type of contact force that opposes the relative motion of two surfaces in contact. It is why you can walk without slipping and why cars can brake to a stop. Tension is another contact force, which occurs in ropes, strings, or cables when they are pulled tight by forces acting from opposite ends. For instance, when you pull a rope in a tug-of-war, the tension in the rope is a contact force.

The normal force is the support force exerted upon an object in contact with another stable object. For example, when a book rests on a table, the table exerts an upward normal force on the book, balancing the downward force of gravity. Applied force is any force that is applied to an object by a person or another object. For example, when you push a door to open it, you are applying a contact force.

Understanding these forces helps us analyse various physical situations, predict the motion of objects, and solve problems related to mechanics. By recognising and calculating contact forces, we can better understand the principles of motion and the interactions between different objects in our everyday lives.