Drop two balls of very different mass down an airless column and time them. Their weights differ, but the fall time and impact speed come out identical — because in a vacuum only gravity acts, and gravity gives every mass the same acceleration. Drag the sliders and press Drop to see it happen.
Two sliders control the physics and two control only the picture. Drop height and gravity are the ones that change the answer: raise the height and both the fall time and impact speed grow; raise gravity and the fall gets quicker but harder-hitting. The gravity preset buttons snap straight to the Moon, Mars, Earth and Jupiter values, so you can compare worlds in a single click. The two mass sliders, by contrast, only ever move the weight readouts.
That split is the whole point of the lab. Set Mass A to a tenth of a kilogram and Mass B to ten kilograms, then press Drop. The weight figures sit a hundredfold apart, yet the two balls stay locked together the whole way down and the single fall-time and impact-speed readouts never flicker. Watching one number refuse to change while another swings wildly is far more convincing than being told the masses do not matter — it is free fall physics and the equations of motion proving themselves.
The numbers behind it are short. The fall time is t = sqrt(2h/g) and the impact speed is v = sqrt(2gh), and neither one contains the mass at all. That is why dragging a mass slider from one end to the other leaves the timing untouched: mass has simply been cancelled out of the maths of falling. Press Drop after each change and the strobe trail spaces out as the balls speed up, tracing the acceleration for you.
One thing is left out on purpose: air resistance. The column here is a vacuum, so nothing slows the fall. In the real world a falling object eventually stops speeding up, and if you want to explore that limit, open the terminal velocity tools or size a specific drop with the free fall calculator. For everything else, browse the full simulation collection.
Because in free fall every object accelerates at the same rate, g, whatever its mass. The fall time t = sqrt(2h/g) contains only the height and gravity, not the mass, so two balls dropped together always land together. Drag either mass slider from 0.1 kg to 10 kg and the fall-time and impact-speed readouts do not move a single digit.
It sets g, the gravitational field strength, from Moon at 1.62 up to Jupiter at 24.79 m/s². A stronger g makes both balls fall faster, so the fall time drops and the impact speed rises. The four preset buttons jump straight to the Moon, Mars, Earth and Jupiter values, and the slider sweeps everything in between.
No. The column is treated as a vacuum, so the only force is gravity and the two masses fall identically. Real dropped objects meet air resistance, which is what makes a feather flutter while a coin plummets. For that effect, use the terminal-velocity tools, where the drag force is the whole point.
Set the height and gravity to match your problem, read the fall time t = sqrt(2h/g) and impact speed v = sqrt(2gh) from the panel, then press Drop to watch it play out. If your worked answer differs, check whether you used g = 9.81 m/s² and whether you squared the time correctly in h = ½gt².
A 100 m drop on the Moon really takes about 11 seconds, too long to watch comfortably, so the simulator compresses any fall longer than 2.5 seconds into 2.5 seconds of screen time and labels the speed-up, for example ×4.4 faster than real time. The readouts always show the true physical seconds and metres; only the playback is sped up.