|I have a question whose answer will settle an
argument that my friend and I are having regarding
atmosphere and gravity. The question is: Would we
bounce around, as astronauts do on the moon, if we
had no atmosphere? (if we were able to survive
without an atmosphere that is, so purely
theoretical) I explained to my friend that gravity
is not dependent on the atmosphere, in fact
gravity is what keeps the atmosphere from
‘floating’ away into space. I also explained that
we would still be held to the ground because of
gravity even without an atmosphere. He, however,
is of the opinion that if Earth had no atmosphere,
we would be able to bounce around – he thinks that
the atmosphere is what keeps gravity ‘in’ instead
of vice versa. |
|Question Date: 2019-04-12|
It is indeed
gravity which keeps the atmosphere around the
earth and which holds us to the ground.
Gravity is the force which attracts bodies
toward each other due to their mass. The
strength of this attraction depends on the masses
of the bodies and the distance between them through:
F = G*(m1 * m2)/r2
(G is the universal gravitational constant,
m1 and m2 are the masses of
the bodies, and r is
the distance between the centers of mass of the
Astronauts on the moon "bounce" because
gravity on the Moon is so much lower than that of
Earth (by a factor of ~6) that the astronauts were
strong enough to jump and fling themselves around
simply through "normal" (for the surface of Earth)
motions. The lack of atmosphere has nothing to
do with this bounciness. In this video,
an astronaut on the (International Space
Station) ISS is in an environment with an
atmosphere but with low (essentially zero)
effective gravity. Similarly to moving on the
Moon, moving requires a sort of bouncing rather
than standard walking motions that work on Earth.
[Interestingly, part of the reason astronauts fell
over so much when on the Moon is because
gravity is important for the sense of up and
down. The low
gravitational field of the Moon meant the
subconscious parts of the astronauts' nervous
associated with balance couldn't decide which way
to try to point their heads.]
No - the reason why astronauts on the moon bounce
around is because the moon's gravity is about one
sixth as strong as Earth's gravity.
The gravity of an object depends on the mass of
the object. Earth is bigger than the moon, has
more mass, and thus more gravity.
Gravity is what keeps the atmosphere from boiling
off into space, but the amount of atmosphere is a
little bit more complicated than just gravity. For
example, Venus has a much thicker atmosphere than
Earth, but about the same amount of gravity.
Still, without gravity, the atmosphere would
In short, you are correct.
The gravity of a planet or moon depends on the
size of the planet or moon. Earth is big, so
it has stronger gravity than the puny moon.
Earth's gravity pulls us and the gas molecules
toward Earth, forming the atmosphere and
keeping us on the ground. You're right.
Here are some answers from Quora that have
"The atmospheric pressure and gravity are very
closely related. The force of gravityis acting on
mass of gas particles in the atmosphere and
pressing towards Earth's centre. Gravity is a
binding, pull force. ... Our weight is also due to
gravity and always pressing downwards."
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