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Penny drop impact calculator

Would a penny dropped from a skyscraper really kill someone? This tool applies quadratic air drag to find the terminal velocity a coin actually reaches, its true impact speed after any fall height, and the kinetic energy — debunking the famous myth with physics.

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The Penny drop impact calculator turns Drop height, Height unit, Object, Custom mass (g) — custom only, Custom diameter (mm) — custom only, Orientation (falling attitude) into Terminal velocity, Impact velocity (with drag), Impact velocity if no air (vacuum), Kinetic energy at impact, Danger level, instantly and for free. For instance, with Drop height = 380, Height unit = meters (m), Object = US penny (2.5 g, 19 mm), Custom mass (g) — custom only = 2.5, Custom diameter (mm) — custom only = 19 and Orientation (falling attitude) = Tumbling (realistic) it returns Terminal velocity = 11.08 m/s, Impact velocity (with drag) = 11.08 m/s and Impact velocity if no air (vacuum) = 86.331 m/s.

How to use it

  1. Enter your values: Drop height, Height unit, Object, Custom mass (g) — custom only, Custom diameter (mm) — custom only, Orientation (falling attitude).
  2. Read the result instantly: Terminal velocity, Impact velocity (with drag), Impact velocity if no air (vacuum), Kinetic energy at impact, Danger level.

Frequently asked questions

How does the Penny drop impact calculator work?

It takes Drop height, Height unit, Object, Custom mass (g) — custom only, Custom diameter (mm) — custom only and Orientation (falling attitude) and derives Terminal velocity, Impact velocity (with drag), Impact velocity if no air (vacuum), Kinetic energy at impact and Danger level from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

6 values: Drop height, Height unit, Object, Custom mass (g) — custom only, Custom diameter (mm) — custom only and Orientation (falling attitude). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Drop height = 380, Height unit = meters (m), Object = US penny (2.5 g, 19 mm), Custom mass (g) — custom only = 2.5, Custom diameter (mm) — custom only = 19 and Orientation (falling attitude) = Tumbling (realistic), the calculator returns Terminal velocity = 11.08 m/s, Impact velocity (with drag) = 11.08 m/s and Impact velocity if no air (vacuum) = 86.331 m/s. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Drop height = 760, Height unit = feet (ft), Object = US nickel (5 g, 21 mm), Custom mass (g) — custom only = 5, Custom diameter (mm) — custom only = 38 and Orientation (falling attitude) = Flat face-on (max drag) instead, Terminal velocity goes from 11.08 m/s to 13.438 m/s — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which “Height unit” option should I choose?

You can pick between « meters (m) », « feet (ft) » and « stories (×3 m) ». Each one changes what the calculator works out, so switch and compare — the default is « meters (m) ».

What does it give for smaller values?

Scaled down to Drop height = 0, Height unit = meters (m), Object = US penny (2.5 g, 19 mm), Custom mass (g) — custom only = 0, Custom diameter (mm) — custom only = 0 and Orientation (falling attitude) = Tumbling (realistic), Impact velocity (with drag) comes out at 0 m/s. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Checking a homework answer, sizing something before building it, and getting an order of magnitude before committing to a design — a torque on a bolt, the force a spring returns, the frequency a circuit resonates at, how long light takes to arrive.

What is the most common mistake?

Feeding in a value in the wrong unit. Physics formulas assume SI throughout, so grams instead of kilograms or centimetres instead of metres shifts the answer by powers of ten without any warning.

How accurate is it, and what are the limits?

Reality check: a US penny tops out near 11 m/s (~25 mph) and carries far too little energy to kill — the skyscraper-penny myth is busted. Drag uses ρ_air = 1.225 kg/m³ and an orientation-dependent drag coefficient.

What is the difference between the Penny drop impact calculator and the Voltage drop calculator?

This one returns Terminal velocity and Impact velocity (with drag); the Voltage drop calculator returns Voltage drop (V) and Voltage drop (%). That is the whole difference — open the one whose figure you need.

Further reading

All guides →
ExplainerProjectile Motion Explained: Range, Height, Flight Time — and Why 45° Is Not Always BestThree formulas cover the whole of projectile motion on level ground. The catch is level ground: the moment launch and landing heights differ, the 45° result stops being true.ExplainerHow the Doppler Effect Works: The Formula, the Sign Convention, and Why Moving the Source Is Not the Same as Moving the ListenerFor sound, f' = f(v + v_o)/(v − v_s) — and getting the signs backwards is the classic error. Here is the convention spelled out, a 440 Hz source computed at four speeds, and why light needs a different equation entirely.ExplainerWhat Is the Reynolds Number? The Formula, the Units That Cancel, and Why 2 300 Is Only for PipesRe = ρvL/μ compares inertia with viscosity, and the units really do cancel. See the number worked out for honey, a household pipe, an artery, a swimmer and a wing — and why the 2 300 threshold belongs to pipe flow alone.ExplainerHow Buoyancy Works: Archimedes' Principle, and Why Ice Floats With 10.5 % Above WaterThe upward force equals the weight of the fluid pushed aside. That one sentence decides whether something floats, and if it floats, exactly how much of it stays under.GuideThe Four Kinematics Equations: Which One to Use, and What Each One Leaves OutFive variables, four equations, and each equation is missing exactly one of them. Choose by looking at the variable the question never mentions.ExplainerWhat Is Kinetic Energy? The KE = ½mv² Formula ExplainedKinetic energy is the energy of motion, given by KE = ½mv². Learn what the formula means, why speed matters most, and see worked examples in joules.