In normal air, a feather drifts slowly while a coin drops fast. That gap is entirely due to air pushing back on the feather as it falls. Place both inside a clear plastic tube sealed with rubber stoppers, then flip it — the coin beats the feather easily. Now pump the air out with a vacuum pump and flip again. With no air to push back, the feather falls almost as fast as the coin. Let the air back in and the difference returns immediately.

Gravity pulls every object down, regardless of how heavy or light it is. That might seem obvious, but in normal air the feather drifts while the coin drops fast — air resistance clouds the picture. To remove that variable, you place a coin and a feather inside a clear plastic tube sealed with rubber stoppers and pump the air out with a vacuum pump. Flip the tube in normal air first: the coin wins easily. Pump the air out and flip again. With no air resistance, the feather falls almost as fast as the coin. Let the air back in and the difference returns immediately.

In normal air, a feather drifts slowly while a coin drops fast — each reaches a different top falling speed because air slows them unequally. You seal a coin and a feather inside a clear plastic tube, flip it, and watch the coin beat the feather easily. Then you pump the air out with a vacuum pump and flip the tube again. With no air present to slow either object, the feather falls almost as fast as the coin. Let the air back in and the difference returns immediately, showing that air is what sets each object’s falling speed limit.