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Newton's second law
Beginner
Net force equals mass times acceleration.
ΣF = maThe net force on a body equals its mass times its acceleration, ΣF = ma, and acceleration points along the net force. Apply it separately to each axis.
A 5 kg block pushed by 20 N with 5 N friction: a = 15/5 = 3 m/s².
Use the net force, including friction, not just the applied force.
In more detail
Newton's second law states that the net force on an object equals its mass times its acceleration, F = ma. Acceleration is in the direction of the net force.
Real-world uses
- Engineers size engines and brakes using F = ma for the vehicle's mass and target acceleration.
- Rocket designers calculate thrust needed to achieve a given acceleration.
- Car designers use F = ma to work out how much engine force is needed to reach a given acceleration for a car of known mass.
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Frequently asked questions
Is F = ma true for every force?
It applies to the net force, the vector sum of all forces acting on the object.
Does a larger force always mean larger acceleration?
Yes, for the same mass. For larger mass, the same force gives smaller acceleration.
Is the net force or the single force used in F = ma?
The net force, which is the vector sum of all forces acting on the body.
Related topics in Newton's Laws & Forces
Contact and non-contact forces · Newton's first law · Inertia · Units of force · Newton's third law · Weight and normal force