A hammer and a feather fall together on the Moon because the Moon has almost no atmosphere to create meaningful air resistance. Both objects experience the same gravitational acceleration when dropped from the same height. Apollo 15 astronaut David Scott demonstrated this directly in 1971.
What happened in the Apollo 15 experiment?
Near the end of the mission’s final moonwalk, Scott held a geological hammer and a falcon feather at approximately the same height and released them together. The television audience watched both reach the lunar ground at essentially the same moment.
Why doesn’t that happen with a loose feather on Earth?
Gravity pulls both objects downward on Earth as well, but air exerts a resisting force on them. The feather has a broad surface relative to its weight, so the air noticeably slows it. A dense hammer is much less affected in ordinary falls. Remove the air, and the dramatic difference disappears.
Does a heavy object have a stronger gravitational force?
Yes, a heavier object has a larger gravitational force acting on it, but it also has proportionally more inertia. In the ideal free-fall case, those effects cancel when calculating acceleration, so the hammer does not accelerate faster merely because it is heavy.
How fast do things fall on the Moon?
The Moon’s surface gravitational acceleration is approximately 1.62 meters per second squared, versus about 9.81 on Earth. A dropped object therefore speeds up more slowly on the Moon. Both the feather and the hammer share that lunar acceleration in the near-vacuum.
What about dropping them inside a vacuum chamber on Earth?
A suitable laboratory vacuum removes most air resistance and can show a similar result: a feather and a dense object fall together when released simultaneously. The experiment does not require the Moon’s weaker gravity; it requires negligible drag.
FAQ
Were the objects exactly the same weight?
No. That is the point: different masses can fall with the same acceleration when air resistance is negligible.
Would two objects land together from different heights?
Not necessarily. The demonstration compares objects released at approximately the same height and time.
Is weight the same on Earth and the Moon?
No. Mass remains essentially unchanged, but weight depends on local gravity. See how to calculate weight on the Moon.
NASA source
NASA’s Apollo 15 hammer-feather demonstration includes the mission account and explains the physics. This article describes the historic experiment; the illustrations are conceptual, not photos of the original drop.
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