The Gravity of the Situation


Oh Aunty Acid, I hate to be the bearer of bad news, but…there is gravity on the Moon.  There’s gravity everywhere.

I’ve seen this misconception enough that I figure it warrants some discussion.  Take a trip back in time with me to the days of Sir Isaac Newton.  Newton is known for many things, including his Law of Universal Gravitation, which says that any two particles in the Universe will attract each other with a force that is proportional to the product of their masses, and inversely proportional to the square of the distance between them.

In plain English, imagine you have two particles (and particles can mean any two objects, large or small.  They don’t have to be protons or electrons, for example.)  Let one of the particles have a mass of A kilograms, while the other particle has a mass of B kilograms.  As long as the two particles stay the exact same distance apart, then the gravitational pull between them will be proportional to AB.  If you increase the mass of either particle, then you increase the gravitational pull between them by that same ratio.  For example, double the mass of Particle A only, and the gravitational pull between A and B will also double.  If you double both masses, then the gravitational pull between them will quadruple, since 2 x 2 = 4.

The second part of Newton’s L.U.G. tells us that the gravitational attraction between any two “particles” decreases as the particles get farther apart from each other.  You might expect that, but the force doesn’t drop off in a linear way.  Instead, the force decreases with the square of the distance.  So let’s say that you keep the masses of A and B the same, but double the separation between them.  The gravitational force will drop to (1/2)², or 1/4 of its original value.  If you triple the separation between the particles, the gravitational pull drops to (1/3)² = 1/9 of its original value.

As you can see, gravity drops off rapidly with increasing distance.  Perhaps this is what leads some people to conclude that the Moon has no gravity; after all, it is quite far away from Earth by human standards.

But the Moon does have its own mass – quite a lot of it, in fact – and it has its own gravitational pull on nearby objects, separate and distinct from the Earth’s gravitational tug.  In fact, if you fly your spaceship to a point about 66,000 kilometers away from the Moon, the Moon’s gravity will be the dominant force that guides your trajectory.  This is what happened with the Apollo missions (indeed, with any lunar mission, manned or unmanned, that has ever successfully reached its target).

On the surface of the Moon, you experience a gravitational pull that is about 1/6 of what you experience on Earth.  Again, that’s not because you’re so far away from Earth; it’s because the Moon’s mass – albeit large – is still significantly less than the Earth’s mass.  When you stand on the Moon, there is simply less mass beneath your feet pulling you downward.

Contrary to what some people believe, there is even gravity in outer space, between the Earth and Moon, and anywhere else in the Universe that you care to look for it.  Remember, the gravitational influence of a body drops dramatically as you get farther from the body, but it never actually drops to zero.  Plug in any number you want for x, and the expression (1/x)² will never, ever be equal to zero.  So even when a spacecraft is far from Earth, far from the Moon, far even from the Sun, there will be a gravitational influence guiding its path.

(But wait a minute, you might interject, if there’s gravity everywhere, how come the astronauts float around inside the space station?  Check and mate, mister science nerd!)

Strangely enough, astronauts float inside the space station not because they have escaped gravity, but because gravity affects the space station as well as the astronauts.  The entire kit and kaboodle is in a state of free fall, just like on the Drop Zone ride.  The astronauts are indeed falling…and the space station is falling around them.  And they avoid falling to Earth because the station is also moving sideways fast enough that it falls around Earth instead of down to Earth.  But that’s a topic for another day.

So let’s summarize this meme’s misconception: there is gravity on the Moon (and everywhere else) so your saggy parts will continue to sag, albeit less severely.  But instead of trying to figure out how to get to the Moon, Aunty Acid, why don’t you focus on loving yourself the way you are?


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