Drop a ball from a 100 m tower on the Moon, click at every red flash, and recover the lunar gravity g from your own reaction time.

Stopwatch 0.00s
Click anywhere on the scene to drop the ball and start the clock.
Marks recorded 0 / 20
Next mark 5 m

Tip: 1.0× keeps your reaction-time noise honest.

#x (m)your t (s)true t (s)Δt
Live analysis

Time vs. distance

updates every click
Estimated g (from your clicks) –
True lunar g 1.625 m/s²
Mean reaction delay –

Red points are your clicks. Blue is the true lunar curve and green is the live fit x = ½ ĝ t². Their horizontal gap captures your reaction delay.