Physics Tools
What It Does
Works out force, mass, or acceleration from the other two using Newton’s second law (F = ma), and optionally the weight (W = mg) and the maximum friction force (f = μN). Everything runs in your browser.
How to Use It
- Enter exactly two of force, mass, and acceleration, leaving one blank.
- Read the computed value and the equation used.
- Optionally pick a planet for weight, or enter
μ(and a normal force) for friction. - Click Copy on any computed value.
About Newton’s Second Law
Newton’s second law states that the net force on an object equals its mass times its acceleration, F = ma. Rearranged, it also gives the acceleration a known force produces (a = F/m) or the mass implied by a force and an acceleration (m = F/a). A common source of confusion is mass versus weight: mass (kilograms) measures how much matter an object contains and never changes, while weight (newtons) is the gravitational force on that mass, W = mg, and so depends on where you are — the same 10 kg weighs about 98 N on Earth but only about 16 N on the Moon. Friction opposes motion along a surface; its maximum magnitude is f = μN, where N is the normal (support) force — on a flat surface simply the weight mg. Because force, acceleration, and displacement are vectors, signs encode direction: a negative force or acceleration points opposite to your chosen positive direction. Everything here is computed on your device.
Example
m = 10 kg, a = 2 m/s² → F = ma = 20 N; on Earth W = mg = 98.1 N.
Frequently Asked Questions
How many values do I need to enter?
Exactly two of force, mass, and acceleration — the third is computed from F = ma. The weight and friction panels work independently from the data you give them.
What’s the difference between mass and weight?
Mass is the amount of matter (kilograms) and is the same everywhere. Weight is the gravitational force on that mass (W = mg, newtons) and changes with local gravity, so an object weighs less on the Moon than on Earth.
Why can a force or acceleration be negative?
They are vectors. A negative value simply means it points opposite to the direction you chose as positive — for example a braking force that opposes forward motion. Mass, by contrast, is always positive.
What does friction depend on?
The maximum friction force is f = μN: the coefficient of friction μ (how “grippy” the surfaces are) times the normal force N pressing them together. On a level surface N = mg. It does not depend on the contact area or speed.
Is my data sent to a server?
No. Every calculation runs locally in your browser; nothing you enter is transmitted or stored.