Free Fall Calculator
Drop something from a known height and, ignoring air resistance, both the fall time and the impact speed follow directly — the calculation behind everything from a dropped phone screen to a skydiving physics problem.
Inputs
Result
3.029 s
Impact speed 29.71 m/s
How the free fall calculator works
Fall time: t = √(2h ÷ g).
Impact speed: v = t × g (equivalently, √(2gh)).
Worked example: dropped from 45 m
- t = √(2×45 ÷ 9.81) = √9.174 ≈ 3.03 s.
- Impact speed = 3.03 × 9.81 ≈ 29.7 m/s (about 107 km/h).
Common mistakes to avoid
Ignoring that this assumes no air resistance
Real falling objects, especially light or large-surface-area ones like a sheet of paper or a skydiver at high speed, experience significant air resistance that this idealised calculation doesn't account for — actual fall time and speed can differ substantially for such objects.
Assuming heavier objects fall faster
In the absence of air resistance, all objects fall at the same rate regardless of mass — mass doesn't appear anywhere in either formula, which is exactly the famous result usually attributed to Galileo.
Frequently asked questions
Why doesn't mass appear in either formula?
Gravitational acceleration is the same for all masses in the absence of air resistance — a heavier object experiences more gravitational force, but also has proportionally more inertia resisting that force, and the two effects exactly cancel.
How significant is air resistance in practice?
For dense, compact objects falling relatively short distances (like a dropped tool from a few metres), air resistance is often negligible. For light objects, long falls, or high speeds, it becomes significant and this idealised calculation increasingly overstates the real impact speed.
What does terminal velocity have to do with this?
Terminal velocity is the speed at which air resistance exactly balances gravity, so the object stops accelerating — this calculator's ever-increasing impact speed with height eventually becomes unrealistic once terminal velocity would actually be reached first.
How would this change on the Moon?
Enter the Moon's gravity (about 1.62 m/s²) instead of Earth's — the fall would take considerably longer and result in a lower impact speed for the same height, exactly as seen in footage of Apollo astronauts dropping objects.
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