Free Fall Calculator — Drop Time, Height, Impact Speed

Real-world use cases

• Check a kinematics homework answer

  The problem set asks how long a stone takes to fall from a 45 m bridge and how fast it hits the water. Enter h = 45, leave g at 9.81, and read t ≈ 3.03 s and v ≈ 29.7 m/s straight off. Then work it by hand and compare. When the numbers disagree, it is almost always a dropped factor of two in ½gt² or a square root left off the velocity, and seeing the right answer makes the slip obvious.

• Reconstruct a fall from the landing speed

  You know an object hit the ground at 25 m/s but not how high it started. Switch to impact-speed mode, enter 25, and the tool returns a fall of about 31.9 m over 2.55 s using h = v²/(2g) and t = v/g. This is the kind of back-calculation you need when only the final velocity was measured, for a lab write-up or a physics estimate.

• Compare gravity on the Moon and Mars

  Teaching why the same drop behaves differently across worlds, set a 10 m height and tap through Earth, Moon, and Mars. The fall time jumps from 1.43 s on Earth to about 3.51 s on the Moon, and the impact speed drops with it. Sharing the resulting link lets students reopen the exact comparison without re-typing anything.

• Sanity-check a drop test or stunt timing

  A maker or filmmaker needs to know how long a prop falls from a known rig height so a camera or trigger can be timed. Enter the height in time mode flipped to height mode, read the fall time, and you have the window to work with. Because the model is the no-air upper bound, real light props arrive a touch later, which is the safe direction to err.

Common pitfalls

• Forgetting the factor of one half in h = ½gt². Writing h = gt² doubles the distance, so a 2 s fall looks like 39.2 m instead of the correct 19.62 m. The half comes from integrating constant acceleration over time; it is not optional.

• Confusing fall distance with fall speed. Distance grows with t² while speed grows with t, so after the first second the object is moving at 9.81 m/s but has only dropped 4.9 m. Plotting them as if both were linear is a common slip.

• Expecting real objects to match the result. This model has no air resistance, so a feather, a flat sheet, or any long high-speed drop will fall slower than predicted as drag builds toward terminal velocity. Use it as the vacuum upper bound, not the literal real-world value.

Privacy