Why do we weigh less on the moon?
Weight is how hard things (floor, ground, etc.) push up on us. Note, I
said up and not down. The downward force is the gravitational force. The
gravitational force depends on mass (the amount of material you are made
of) and the gravitational field intensity. If the gravitational field
intensity is lower, as it is on the moon, the gravitational force is lower
for the same mass.
Now, what does this have to do with weight? If you are standing still, the
upward push by the ground is equal to the downward push due to gravity. If
the gravitational force is less, the upward push is less, hence, you weigh
So how do you become weightless? Just jump! While you are in the air, you
have no supporting force. The gravitational force is still there (the
earth eventually catches you after about a second).
---Nathan A. Unterman
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Update: June 2012