Force Calculator

The formula this calculator uses

F = m x a

F

Force in newtons, the net push or pull that changes motion

m

Mass in kilograms, the amount of matter and a measure of inertia

a

Acceleration in metres per second squared, the rate of change of velocity

W

Weight in newtons, equal to m x g, the force gravity exerts

g

Standard acceleration due to gravity, 9.80665 metres per second squared

How to check the result by hand

1. 1

   Put every quantity into SI units first

   Mass belongs in kilograms and acceleration in metres per second squared. A 1200 kilogram car at 3 metres per second squared is already in the right form, so no conversion is needed before the multiplication.

2. 2

   Multiply mass by acceleration for the net force

   1200 x 3 = 3600, so the net force is 3600 newtons. This is the force that actually changes the car's speed, not the force the engine produces, which must also overcome friction and drag.

3. 3

   Compute the weight separately with W = m x g

   Weight is a different question and a different formula: 1200 x 9.80665 = 11767.98 newtons. Keeping the two calculations apart stops the weight from being mistaken for the force needed to accelerate.

4. 4

   Check the direction and subtract opposing forces

   The second law uses the net force, so any friction or drag acting against the motion is subtracted. If 1000 N opposes the car, the engine must supply 4600 N to leave 3600 N of net force.

5. 5

   Sanity-check against the weight and convert if needed

   The 3600 N of net force is only 0.30591486389337846 of the car's 11767.98 N weight, which is exactly 3 m/s^2 divided by 9.80665. Converting to imperial units, 3600 N is 809.3121951589578 pounds-force.