Calculator
Net force98.1 N
Method, variables and units
Force Calculator
Formula: F = m x a
Assumption: The calculation uses Newton's second law for net force in an inertial frame.
Worked example
Force Calculator
A 10 kg object accelerating at 9.81 m/s^2 has a net force of 98.1 N.
Force in everyday situations
| Situation | Mass | Acceleration | Net force |
|---|---|---|---|
| Weight of a 1 kg bag on Earth | 1 kg | 9.81 m/s² | 9.81 N |
| Weight of a 70 kg person | 70 kg | 9.81 m/s² | 687 N |
| Same person on the Moon | 70 kg | 1.62 m/s² | 113 N |
| Car braking hard (1,500 kg) | 1,500 kg | 8 m/s² | 12,000 N |
| Lift starting upwards (500 kg cabin) | 500 kg | 1 m/s² | 500 N (plus weight) |
One newton is the force that accelerates 1 kg by 1 m/s². A kilogram-force (kgf), still used on some scales and gauges, is the weight of 1 kg in standard gravity: 1 kgf = 9.80665 N. A car of 1,500 kg that stops from 100 km/h (27.8 m/s) in 3.5 seconds decelerates at about 27.8 / 3.5 ≈ 7.9 m/s², so the tyres must supply a net braking force of roughly 1,500 × 7.9 ≈ 11,900 N.
Common mistakes
- Using weight in kilograms as force: bathroom scales show mass; the force on the floor is mass × 9.81 N.
- Forgetting that F = m × a gives the net force; when gravity, friction or drag also act, the applied force must be larger.
- Using grams instead of kilograms: 500 g is 0.5 kg in the formula.