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What is a force?
Beginner
A push or pull that can change an object's motion or shape.
F = maA force is an interaction that can change a body's velocity or deform it. It is a vector, measured in newtons, and it always comes from another object. The net force, the vector sum of all forces, determines the acceleration.
A 2 N push and a 3 N push in the same direction give 5 N; in opposite directions, 1 N.
Forces are not carried by moving objects; "force of motion" is not a thing.
In more detail
A force is a push or pull that can change an object's velocity or shape. It is a vector, with a magnitude in newtons and a direction.
Real-world uses
- Crash test engineers measure the forces acting on dummies to assess injury risk.
- Physiotherapists design exercises that apply controlled forces to muscles and joints.
- A tug pulling a ship, a hand squeezing a sponge and gravity pulling an apple all show a force changing motion or shape.
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Frequently asked questions
Is a force needed to keep something moving?
No. A force is needed to change motion. An object moving at constant velocity has no net force on it.
What is the SI unit of force?
The newton, equal to one kilogram metre per second squared.
Is a force needed to keep something moving?
No. Once moving at constant velocity, no net force is needed. A force is needed to change the motion, such as to speed up, slow down or turn.
Related topics in Newton's Laws & Forces
Contact and non-contact forces · Newton's first law · Inertia