Reaction Force - GCSE Physics Definition

In physics, a reaction force is the force that pushes back when something applies a force on an object or surface. According to Newton's third law of motion, every action has an equal and opposite reaction, which means that forces always come in pairs. For example, if you push against a wall, the wall pushes back with the same amount of force but in the opposite direction. Reaction forces are everywhere around us and help things balance, like when you sit on a chair, the chair exerts a reaction force upwards to support you.