What is a force?

Force: F = m × a. A force is a push or a pull, with a size and a direction, measured in newtons: one newton is about the weight of a small apple. Forces add like arrows, and only the net force changes how something moves.

Read how it works: What is a force? · The history of force and the newton · More boxes on Glassbox

Chapters in this interactive model

1. A push or a pull, with a size and a direction: Measure forces in newtons, add them as arrows, and find what is left over.
2. Weight, lifts and a click pen: Weight is a force, scales measure pushes, and springs push back.
3. Chains, brakes and a spinning drum: Machines move forces around, make them bigger, and have to survive them.
4. Every push has a partner: Forces come in pairs. When the ones on a single object cancel, it stays put.
5. Four forces, and three myths: Every push you feel is one of four forces. And forces don’t work quite the way it feels.