L1
Newton's second law
Force equals mass times acceleration.
Practise this conceptNewton's second law connects three quantities: the net force acting on an object, its mass, and the acceleration that force produces.
Double the force on the same mass, and the acceleration doubles too. Double the mass while keeping the force fixed, and the acceleration is cut in half — mass measures an object's resistance to being accelerated, its inertia.
The law only accounts for the net force. If two equal forces pull in opposite directions, they cancel, and the acceleration is zero even though individual forces are still acting.
Key ideas
Requires: Newton's first law, Displacement, velocity and acceleration
Unlocks: Momentum and impulse, Newtonian gravitation, Simple harmonic motion, Work and energy
Formulas
| Symbol | Name | Unit |
|---|---|---|
| force | N (newton) | |
| mass | kg (kilogram) | |
| acceleration | m/s^2 (metre per second squared) |
Common misconceptions
- A constant net force produces a constant velocity, not a constant acceleration.
- For the same force, a more massive object accelerates faster than a less massive one.
- If the net force on an object is zero, the object must be at rest.