Enter Drop Test Inputs
Use SI units. Impact duration is entered in milliseconds.
Formula Used
Impact velocity: v = √(2gh)
Impact time: t = milliseconds ÷ 1000
Velocity change: Δv = v(1 + e)
Average acceleration: a = Δv ÷ t
Average net force: Fnet = ma
Average contact force: Fcontact = m(a + g)
Impact energy: E = mgh
Average pressure: P = Fcontact ÷ A
Here, m is mass, h is drop height, g is gravity, t is contact time, e is rebound coefficient, and A is contact area.
How to Use This Calculator
- Measure the object's mass in kilograms.
- Measure the vertical drop height in metres.
- Enter the estimated or measured impact duration in milliseconds.
- Set rebound coefficient to zero for no bounce.
- Enter contact area when pressure information is useful.
- Keep standard gravity unless your test environment needs another value.
- Select the calculation button and review the result panel above.
Example Test Data
| Mass | Height | Impact duration | Rebound | Average contact force |
|---|---|---|---|---|
| 2.0 kg | 1.0 m | 20 ms | 0.00 | 462.48 N |
| 5.0 kg | 0.8 m | 12 ms | 0.10 | 1,864.56 N |
| 10.0 kg | 1.5 m | 8 ms | 0.25 | 8,573.09 N |
Example values are rounded. Use your own measurements for design decisions.
Understanding Drop Test Results
Understanding Drop Test Force
A drop test measures the load created when an object hits a surface. The load depends on more than mass. Drop height creates speed before contact. Stopping time controls how rapidly momentum changes. A short time creates a larger average force. This calculator uses milliseconds because many real impacts happen very quickly. It also includes rebound. Rebound increases the momentum change. Therefore, it can increase the calculated contact force.
Why Milliseconds Matter
Impact duration is often the strongest input. A package landing on foam may stop over many milliseconds. A steel part hitting concrete may stop much sooner. Doubling the stopping time approximately halves the momentum-based force. This relationship helps compare protective materials. It also explains why cushioning reduces damage. Use measured duration whenever possible. High-speed video, force sensors, and instrumented drop towers can provide better values.
Velocity Before Contact
The calculator finds impact speed from drop height and gravity. It assumes free fall with negligible air resistance. This assumption works well for compact, dense test objects. Very light or broad objects may experience noticeable drag. In those cases, the calculated speed can be too high. Use a measured velocity when drag is important. The displayed energy still provides a useful starting point for test planning.
Average Contact Force
The shown force is an average contact force. It is not the highest force during impact. Real force histories often rise sharply, peak, and then fall. A rigid surface can create a high, brief peak. Foam can create a lower, longer pulse. The calculator adds the object weight to the momentum-based force. This gives the average upward contact force acting during impact. The net force is also shown separately.
Rebound and Restitution
The rebound coefficient describes how much upward speed remains after impact. A value of zero means no rebound. A value of one represents an ideal elastic reversal. Most practical tests fall between these limits. A larger rebound coefficient raises the change in velocity. It therefore raises the predicted average contact force. Enter zero when the object sticks or stops without bouncing.
Pressure and Contact Area
Contact area is optional. When supplied, the calculator estimates average pressure. Convert a realistic contact patch into square centimetres. Do not use the object's entire surface unless it contacts the target. Small contact areas create greater pressure. Pressure can help assess dents, crushing, and localized material damage. It does not replace a detailed stress analysis.
Using Results Safely
Treat results as screening estimates. Actual peak force can exceed the average force shown here. Material stiffness, impact angle, deformation, fixture compliance, and sensor filtering all affect measured loads. Add a suitable safety margin for design work. Verify critical products through physical testing. Record mass, height, duration, rebound, and surface conditions for each test. Consistent inputs make comparisons more reliable.
Careful interpretation prevents false confidence and supports safer protective design choices overall.
Frequently Asked Questions
1. What force does this calculator show?
It shows estimated average contact force during impact. This includes the force needed to reverse or stop motion and the object's weight. Actual peak force can be higher.
2. Why is impact duration entered in milliseconds?
Many impacts occur in only a few milliseconds. Converting milliseconds to seconds is essential because acceleration and force equations use seconds.
3. Is the result a peak impact force?
No. The result is an average force across the entered duration. A real impact pulse can have a much higher maximum value.
4. What rebound coefficient should I use?
Use zero when the object stops without bouncing. Use a measured coefficient when available. Values between zero and one represent partial rebound.
5. Does a longer stopping time reduce force?
Yes. For the same momentum change, increasing impact duration lowers average acceleration. This lowers average contact force.
6. Can I use grams instead of kilograms?
Convert grams to kilograms first. Divide grams by 1,000. For example, 750 grams equals 0.75 kilograms.
7. Does the calculator account for air resistance?
No. It assumes free fall with negligible drag. This is usually reasonable for compact objects and short drops. Use measured speed for high-drag objects.
8. Why enter contact area?
Contact area enables average pressure estimation. Pressure helps assess local crushing, denting, and material damage near the impact point.
9. Can this be used for angled impacts?
It is intended for vertical impacts. Angled impacts need velocity components, friction effects, and a suitable contact model.
10. What gravity value should I enter?
Use 9.80665 m/s² for standard Earth conditions. Change it only when modelling another location or a controlled environment.
11. Is this enough for a safety-critical design?
No. Use it for preliminary screening and comparison. Safety-critical designs require measured force histories, validated models, and appropriate engineering review.