Estimate average impact force from object mass and velocity using either stopping distance (work-energy theorem) or stopping time (impulse-momentum theorem).
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Average impact force
70,000 N
G-force
101.97 g
Kinetic energy
3500.00 J
Δ velocity
10.000 m/s
Force (N)
70,000
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Science — Physics
When a moving object stops, the kinetic energy it carries must be absorbed over the stopping distance or stopping time. This determines the average impact force. Understanding impact force is fundamental to crash safety engineering, fall protection design, and sports equipment testing.
The work-energy method uses F = ΔKE / d, where d is the stopping distance. A car travelling at 60 km/h (16.67 m/s) with mass 1500 kg has KE = 208,375 J. If it stops over 0.5 m (crumple zone), average force ≈ 416,750 N — about 28 g-forces on the occupants. The impulse-momentum method uses F = mΔv / t; the same car stopping in 0.03 s gives F = 1500 × 16.67 / 0.03 ≈ 833,500 N.
G-force is the ratio of impact deceleration to standard gravity (9.80665 m/s²). Humans can tolerate brief accelerations up to 20–50 g depending on direction and duration, but sustained or repeated exposure to even 5–10 g can cause injury. Race car roll cages and airbag systems are designed to extend stopping time and distance, reducing peak g-force within survivable limits.
Frequently asked questions
Force equals the change in kinetic energy divided by stopping distance. Doubling the stopping distance halves the average force. This is why crumple zones in cars, foam padding in helmets, and gymnastics mats all work by increasing the distance over which kinetic energy is absorbed.
This calculator gives the average force over the entire stopping distance or time. Real impacts involve complex force curves; peak force can be several times the average. Detailed crash analysis requires finite-element simulation or instrumented testing.
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