Case 1
- Mass of the object
- 80kg
- Speed at impact
- 10m/s
- Stopping distance
- 0.5m
8,000.00N
Open with these valuesImpact Force Calculator
8,000.00N
Result: 8,000.00 NAn impact spreads the kinetic energy over the stopping distance, so the average force is ½mv² divided by that distance. An 80 kg body at 10 m/s stopped over half a metre averages 8000 N; give it a full metre and the force halves. This is the average, not the peak.
Worked examples
Case 2
- Mass of the object
- 1000kg
- Speed at impact
- 20m/s
- Stopping distance
- 1m
200,000.00N
Open with these valuesCase 3
- Mass of the object
- 70kg
- Speed at impact
- 5m/s
- Stopping distance
- 0.2m
4,375.00N
Open with these valuesHow it's calculated
F = ½ × m × v² ÷ d
- StepEnter the mass of the moving object in kilograms.
- StepEnter its speed at the moment of impact in metres per second.
- StepEnter how far it travels while coming to rest — the crush, the padding, the bend of your knees.
- ResultRead the average force over that distance.
Reference table
| Mass, speed, distance | What it is | Average force |
|---|---|---|
| 50, 2, 0.1 | A 50 kg load stopped in 10 cm | 1000 |
| 70, 5, 0.2 | A person landing stiff-legged | 4375 |
| 80, 10, 0.5 | A body at 36 km/h, half a metre of give | 8000 |
| 1000, 20, 1 | A tonne at 72 km/h, one metre of crush | 200000 |
| 1500, 15, 0.8 | A 1.5 t car at 54 km/h | 210937.5 |
Questions
How do I calculate impact force?
Divide the kinetic energy by the stopping distance: F = ½ × m × v² ÷ d. For an 80 kg body at 10 m/s stopped over 0.5 m the energy is 4000 J, so the average force is 8000 N.
Why does a longer stopping distance reduce the force?
The same energy has to be absorbed over a longer path, and force is energy divided by distance — doubling the distance halves the force. Crumple zones, airbags, climbing ropes and bending your knees all work by lengthening that path.
Is this the average or the peak force?
The average, assuming constant deceleration over the distance you enter. Real collisions are not constant, and the instantaneous peak can be several times higher. Use the figure to compare scenarios, not as the maximum at any single instant.
How do I find the impact speed for a fall?
Ignoring air resistance, the speed just before landing is v = √(2 × g × h). A 1.5 m fall gives about 5.4 m/s. Enter that speed together with the mass and how far you sink on landing.
How do I turn the force into g-force?
Divide the force by the object's own weight, that is by m × g. For 8000 N on an 80 kg body that is 8000 ÷ (80 × 9.81) ≈ 10 g. Textbooks round the 9.80665 standard value to 9.81 for this.
Sources and last check
Information, not professional advice.