The formula
F = m · a
| Symbol | Quantity | Unit |
|---|---|---|
| F | Force | N |
| m | Mass | kg |
| a | Acceleration | m/s² |
What it means
A force is what changes an object's motion. The heavier the object, the more force it takes to accelerate it by the same amount, which is exactly what mass measures: resistance to being accelerated.
How to work it out by hand
- Multiply the mass in kilograms by the acceleration in m/s²
- The answer is in newtons
- To find mass or acceleration, divide instead
What is worth knowing
One newton is the force that accelerates one kilogram at one metre per second squared — a modest push, roughly the weight of a small apple, which is a coincidence the Newton story makes hard to forget. The law explains why seat belts matter: stopping is a change in velocity, and doing it over a longer time means less force. A crumple zone works on exactly this principle, extending the collision from milliseconds to tenths of a second and cutting the force by the same factor.