Feather and Hammer
Does a heavy hammer fall faster than a light feather? Drop them side by side on Earth, in a vacuum chamber and on the Moon, and time them both.
- Gravity g
- 1.62 m/s²
- Hammer lands
- Ready
- Feather lands
- Ready
- Feather speed
- 0.00 m/s
The maths, live
No air h = ½ × g × t²1.6 = ½ × 1.62 × t²So t = √(2h ÷ g)t = √(2 × 1.6 ÷ 1.62) = 1.41 sNo air, so mass doesn't matterboth speed up by 1.62 m/s every secondHeavy things don't fall faster. Air is what slows the feather down, so take the air away and they land together!
How it works
Gravity speeds up everything by the same amount, whatever its mass. Without air, anything dropped from rest falls a distance h = ½ × g × t², so the hammer and the feather land at exactly the same moment.
On Earth, air pushes back on falling things. This air resistance (drag) grows as they speed up. A fluffy feather only needs to fall at about 0.6 m/s before drag balances its tiny weight, so it drifts down slowly. In 1971 astronaut Dave Scott tried it on the airless Moon, and the hammer and feather hit the ground together.
Try this
- Drop them on Earth with air. How many times longer does the feather take?
- Now try the vacuum chamber. Is it the mass or the air that made the difference?
- Compare the Moon with the vacuum chamber. Why do both land together in each, but more slowly on the Moon?