Newton's Second Law of Motion formula
| Symbol | Quantity | SI unit | Meaning |
|---|---|---|---|
| F | Net force | N | Net (resultant) force on the body |
| m | Mass | kg | Mass of the body |
| a | Acceleration | m/s² | Acceleration produced |
What is Newton's Second Law of Motion?
Newton's Second Law of Motion: The net force on a body equals its mass times its acceleration; equivalently, force equals the rate of change of momentum. — Isaac Newton, 1687
Newton's second law connects force and motion. A net force produces an acceleration in the same direction, and a larger mass needs a proportionally larger force for the same acceleration. One newton is the force that accelerates 1 kg at 1 m/s².
Remember that F is the net force: add all forces as vectors (thrust, friction, gravity, normal force) before applying the law.
How to use this calculator
- Choose the quantity you want to find in the Calculate menu. It is highlighted as the result field.
- Enter the known values. Scientific notation such as
1.6e-11is accepted. - Select a unit for each value. Units are converted to SI automatically.
- The answer updates as you type. Open Show calculation steps to see the working, or use Copy result to share a link with your inputs.
Worked example
What net force accelerates a 1200 kg car at 3 m/s²?
- F = 1200 × 3 = 3600 N (3.6 kN).
Frequently asked questions
What is the difference between mass and weight?
Mass (kg) is the amount of matter. Weight is the gravitational force on it, W = mg, measured in newtons. A 10 kg mass weighs about 98 N on Earth and 16 N on the Moon.
Does F = ma hold at very high speeds?
No. Near the speed of light you must use relativistic momentum, and the simple F = ma no longer applies.