A parachute works because air pushes back. Cut a large circle from a plastic bag, poke six holes around the edge, and tie six equal strings to the holes. Attach a small toy to the loose ends and toss the whole thing from a high spot. The plastic fills with air and the toy floats down gently. Gravity still pulls it toward the ground, but that pushing-back force — the air resistance — slows the fall.

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.

Air pushes back harder on some shapes than others, even when the total surface area stays the same. Cut four parachutes from plastic bags — a triangle, a square, a rectangle, and a circle — each at 500 square centimeters. Attach strings and a small washer to each, then drop them from a second-floor balcony while timing each fall with a stopwatch. The round parachute falls the slowest. The triangular one falls the fastest. Same area, different shape — and the difference in that pushing-back force is clear in the data.