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What is a force?

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Quick answer

A force is a push or a pull that can change an object's motion, direction, or shape. Forces are why things speed up, slow down, fall, or stay still — from gravity holding you to the ground to friction stopping a rolling ball.

Key things to understand

  1. A force has both size and direction, and is measured in newtons (N).
  2. Forces cause acceleration: Newton's second law says force = mass × acceleration (F = ma).
  3. Forces come in pairs — for every action there's an equal and opposite reaction (Newton's third law).
  4. Common forces include gravity, friction, tension, and the normal (support) force.
  5. When the forces on an object are balanced, its motion doesn't change; when unbalanced, it speeds up, slows down, or turns.

People also ask

What are the four fundamental forces?
Gravity, electromagnetism, the strong nuclear force, and the weak nuclear force — these underlie every interaction in the universe.
What's the difference between mass and force?
Mass is how much matter an object contains; force is the push or pull acting on it. Weight is actually the force of gravity on a mass.
Can a force exist without movement?
Yes. If you push a wall it doesn't move, but you still apply a force — the wall pushes back equally, so the forces are balanced.