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Newton’s second law calculator

GCSEA-level Forces

The resultant force on an object equals its mass multiplied by its acceleration.

F = m a

This free calculator is for GCSE and A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.

Quantity to find

3000 N
m/s²

Working

  1. Write the equation
    F = m a
  2. Substitute the values
    F = 1200 × 2.5
  3. Calculate
    F = 3000 N
  4. Give the answer to 3 significant figures
    F = 3000 N

Worked example

Find F, the resultant force. Given: mass m = 1200 kg; acceleration a = 2.50 m/s².

  1. Write the equation
    F = m a
  2. Substitute the values
    F = 1200 × 2.5
  3. Calculate
    F = 3000 N
  4. Give the answer to 3 significant figures
    F = 3000 N

Symbols and units

SymbolQuantitySI unit
FResultant forceN
mMasskg
aAccelerationm/s²

Newton’s second law: rearranged

  • To find resultant force: F = m a
  • To find mass: m = F / a
  • To find acceleration: a = F / m

Exam tip

F is the resultant (net) force, not just one of the forces acting. Subtract opposing forces first.

Common questions

What is the formula for newton’s second law?

The equation is F = m a, where F is the resultant force (N); m is the mass (kg); a is the acceleration (m/s²).

What units should I use for newton’s second law?

In SI units: resultant force in N, mass in kg, acceleration in m/s². The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange F = m a?

Rearranging gives these forms: to find resultant force: F = m a. to find mass: m = F / a. to find acceleration: a = F / m.

Practise newton’s second law questions

Press the button for a question with random numbers. Work it out on paper first, then type your answer.

Related

Read the full explanation on the Newton’s second law formula page. More forces equations: Weight, Moment of a force, Hooke’s law, Pressure, Pressure in a liquid, Density, Horizontal component of a force, Vertical component of a force. See the full list on the physics equation calculator page.