Example data table
| # | Mass | Height | Stopping distance | Impact velocity (m/s) | Avg contact force (N) |
|---|---|---|---|---|---|
| 1 | 1 kg | 1 m | 10 mm | 4.4287 | 990.47 |
| 2 | 2.5 kg | 2 m | 20 mm | 6.2631 | 2476.2 |
| 3 | 5 kg | 2 m | 50 mm | 6.2631 | 2010.4 |
| 4 | 10 kg | 1.5 m | 30 mm | 5.4240 | 5001.4 |
| 5 | 0.5 kg | 3 m | 15 mm | 7.6707 | 985.57 |
| 6 | 750 g | 150 cm | 8 mm | 5.4240 | 1386.4 |
| 7 | 2 lb | 6 ft | 0.5 in | 5.9891 | 1290.0 |
| 8 | 12 lb | 4 ft | 1 in | 4.8900 | 2615.6 |
| 9 | 3 kg | 1.2 m | 2 cm | 4.8514 | 1794.6 |
| 10 | 1.2 kg | 40 in | 12 mm | 4.4640 | 1008.1 |
Formula used
The calculator first estimates the impact speed from the drop height: v = √(2gh) (no drag), or a quadratic-drag numerical estimate when enabled.
Using the stopping distance method, the average deceleration is: a ≈ v² / (2d). The average contact force (normal force) is then: F̄ ≈ m·a + m·g.
Using the impact time method, the average deceleration is: a ≈ Δv / t, where Δv = v (no rebound) or Δv = (1+e)v with rebound coefficient e. Peak force is estimated by multiplying by your chosen profile factor.
How to use this calculator
- Enter the object mass and drop height, then choose units.
- Select a stopping method: distance (compression) or time (contact duration).
- Set advanced options: profile factor, rebound (time method), or air drag.
- Optionally add contact area to estimate pressure.
- Click Calculate, then download CSV or PDF if needed.
Dropped object impact force guide
Why impact force spikes
A dropped object can produce forces far higher than its weight because the object’s speed must be reduced to zero over a short distance or time. For example, a 5 kg tool dropped from 2 m reaches about 6.26 m/s (no drag) and carries roughly 98 J of kinetic energy before impact. Its static weight is only about 49 N, so impact forces can be tens or hundreds of times larger.
Inputs that change results most
Impact depends most on mass, drop height, and stopping distance or contact time. Doubling height increases speed by √2, while doubling mass doubles force for the same deceleration. Typical contact times range from 5–50 ms for hard impacts, while soft padding can increase stopping distance from 1 mm to 30 mm. You can enter kg, g, or lb, and heights in m, cm, ft, or inches.
Distance method: stiffness and compression
With the distance method, deceleration is estimated by a ≈ v²/(2d). If a 2 kg object hits at 4.4 m/s and stops in 10 mm, average deceleration is about 968 m/s², or ~99 g. Increasing stopping distance to 30 mm cuts that to ~33 g, usually lowering damage. Distance is a good proxy for stiffness: rubber mats compress more than concrete.
Time method: impulse and rebound
With the time method, a ≈ Δv/t. If the same 4.4 m/s impact lasts 15 ms, average deceleration is about 293 m/s². If rebound is included with e = 0.3, Δv becomes (1+e)v, raising the estimate by 30% for time-based results. Shorter times (like 8 ms) can double the force without changing the drop.
Air resistance: when it matters
Air resistance can matter for light or wide objects. Enabling drag uses air density ρ (often 1.225 kg/m³), Cd, and projected area A. A small, dense part may change little over 1–3 m, but a flat plate or box can lose noticeable speed. Try Cd ≈ 0.47 for a sphere, and Cd ≈ 1.05 for a cube.
Peak factor and pressure estimates
Real impacts are not perfectly “flat.” A half‑sine profile gives peak ≈ 1.57× average, while a triangular profile gives peak ≈ 2× average. If you enter a contact area, the calculator also estimates pressure using pressure = force ÷ area.
Use results to compare scenarios, not to certify equipment. In practice.
FAQs
1) Does this calculator give an exact impact force?
Not exactly. It estimates average and peak contact force from simplified physics. Real impacts vary with material stiffness, angle, rotation, and how force spreads through parts. Use it for comparison, screening, and planning, not certification.
2) Which stopping method should I choose?
Use stopping distance when you can estimate compression or crush distance. Use impact time when you have sensor data or a known contact duration. If you are unsure, try both to see how sensitive the result is.
3) What stopping distance is typical?
Hard surfaces can be 1–5 mm, wood or plastic covers may be 5–20 mm, and thick rubber pads can exceed 20–50 mm. Enter a range (minimum, typical, maximum) to understand best‑ and worst‑case forces.
4) How does contact area affect pressure?
Force is unchanged by contact area, but pressure changes. Pressure equals force divided by area, so a smaller contact patch raises pressure sharply. Use the area that actually touches at impact, not the object’s full footprint.
5) When should I enable air resistance?
Enable it for light, wide, or high‑drag objects, and for taller drops where speed might approach a terminal value. For dense tools over 1–3 m, the difference is often small, but testing both settings is quick.
6) What does the peak factor mean?
It converts average contact force to an estimated peak. Flat assumes peak ≈ average, half‑sine uses 1.57×, and triangular uses 2×. Choose a factor that matches the expected force‑time shape of your impact.