|Does the moon have more gravity than Earth because
it has no atmosphere?
|Question Date: 2017-11-16|
Great question! Despite that we can see gravity
when we drop an object and it falls to the ground
and feel gravity by not floating into space when
we jump, gravity is still technically a
Both Newton and Einstein offer different
theories explaining gravity, but we will
focus more generally around your question.
Anything with mass also has a gravity,
and objects with greater mass have a greater
gravity. Distance is also involved, as gravity
weakens with distance. So Earth’s gravity
comes from its mass causing a gravitational
pull on all the mass in your body. That
gravity pull is equal to your weight . So
if you were on a different planet with less
mass than Earth, you would weigh less there.
In the context of the universe, gravity is
what holds the earth in orbit around the sun.
Gravity is also how our universe formed,
pulling space dust together to create stars,
planets, and other space bodies. The moon’s
gravity pulls on Earth’s oceans, causing
tides. Earth pulls on the moon, keeping it
in orbit around Earth.
Earth's mass is 5.9724 x 1024 kg
and the moon's mass is 0.07346 x 1024
kg. This equates to a surface gravity on the
moon of 1.62 m/s2, or 0.165 of Earth's
9.8 m/s2 gravity. The atmosphere
around Earth does not make its gravity weaker.
In fact, Earth's gravity contributes to how
there is even an atmosphere. The gases and
particles that make up the atmosphere are kept
around the surface of Earth due to its gravity
preventing the atmosphere from being lost to
The moon actually has less gravity than the earth,
but not because of the lack of atmosphere. It's
because the moon has much less mass. Mass
is just a measure of how much stuff is there in
something, so a full-sized truck has more mass
than a human. Earth has a lot of mass,
5.97*1024 kilograms, or
96,000,000,000,000,000,000,000 times the mass of
an average adult human! The moon only has
about 1/80th of the earth's mass, so it has
much less gravity than the earth. Earth's
atmosphere is only a tiny part of its total mass,
so the atmosphere doesn't contribute a lot to
the earth's gravity.
Now what is gravity? It is a force
that any one thing with mass can exert on any
other thing with mass. A force is simply a
push or a pull in any direction. When you throw a
ball, for example, you're exerting force on the
ball. We don't typically think about this, but the
floor in your house is continuously exerting force
upwards onto the furniture so the furniture
doesn't fall through because of gravity! With
gravity, two things with mass will want to move
toward each other. However, we humans don't feel
our gravity pulling on another person because it's
not very big, but we do all feel the pull of
Earth's gravity all the time - we're not all
floating in the air, because that would be
happening without Earth's gravity!
Earth's gravity is the reason we fall onto
the ground, the reason we can have activities like
skydiving, and the reason that it's so miraculous
that we can fly in planes.
No - the moon has much less gravity than the
Earth. When you watch videos of the
astronauts from the Apollo program walking around
on the moon, you see them bouncing around because
the moon's weak gravity can't hold them down the
way Earth's gravity holds us down when we walk.
The moon's lack of an atmosphere is in part
because of the moon's weaker gravity, but also due
to other things as well . For instance
Saturn's moon Titan is only somewhat larger than
Earth's moon, and has a very dense atmosphere,
more than what Earth has. Mars is larger than
either moon, and has a much thinner atmosphere.
Venus is almost the same size as Earth, and has an
even thicker atmosphere than Titan does.
The earth actually has more gravity than the
moon. Larger celestial bodies have more
gravitational pull. Your weight actually changes
with gravity. You can think of your weight as
gravitational force pulling you down towards the
center of the earth. If you were standing on
the moon, you would actually feel lighter. A
person weighing 100 lbs on Earth would weigh 17
lbs on the moon. In fact, if there was no gravity,
you would be practically weightless and can start
floating away into space. This is the same reason
why the earth has an atmosphere but the moon does
not. The earth's gravitational pull is strong
enough to hold an atmosphere in place while the
moon's gravitational pull is not strong enough to
do the same.
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