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THE TERM “ZERO-GRAVITY” PROVES MISLEADING WHEN IT COMES
TO FREEFALLING THROUGH SPACE
Engrid
Barnett
RIPLEY'S BELIEVE IT OR
NOT!
From Apollo
12 (1995) to Contact (1997) and the aptly
titled Gravity (2013), we’ve all gotten used to the visual of
astronauts floating around in zero-gravity environments.
You
could say that the idea of space having no gravity is common knowledge, at this
point.
Many
people wouldn’t think twice about why astronauts appear weightless.
The
perceived weightlessness of astronauts is a misnomer, though. So is the concept
of space as a zero-gravity environment.
Space
contains what’s known as microgravity.
Here’s
what it is and how it relates to the images we’re all so familiar with of
buoyant astronauts.
SPACE AND MICROGRAVITY
Let’s
start with the number one question on everyone’s mind, “What the heck is
microgravity?”
Microgravity
refers to the condition of objects or people appearing to be weightless.
For
example, we see the effects of this phenomenon in videos from the space
station, showing individuals and the objects around them suspended in midair.
This
condition occurs not only within spacecraft and space stations but also outside
during spacewalks where astronauts must stay tethered to avoid floating away.
Six astronauts who had been in training at the Johnson Space Center for almost a year are getting a sample of a micro-gravity environment |
When
involved in extra-vehicular activities (EVAs), they secure their
shoes with foot restraints to avoid drifting away.
But
just because these individuals and the objects around them are floating doesn’t
mean they exist in a zero-gravity environment.
Everywhere
in space, a small amount of gravity exists.
Gravity
keeps the sun in place within the more massive Milky Way, and it’s why the
Earth orbits the sun. It also holds the Moon in place as it revolves around the
Earth.
That
said, gravity does weaken due to distance.
For
example, if you could take a spacecraft far enough from Earth, you’d eventually
reach a range where the planet’s gravitational pull diminishes.
Nonetheless,
this is not why people and things float in space.
WHY OBJECTS FLOAT IN SPACE
Orbiting
the Earth at an altitude of 200 to 250 miles, the International Space Station
experiences about 90 percent of the gravity felt on the planet’s surface.
In
other words, if you could climb stairs from the Earth to the space station,
you’d weigh approximately 90 percent of what you do once you hit the top of the
staircase.
This
illustration begs the question, “If 90 percent of the Earth’s gravitational
pull reaches the space station, then why do the astronauts live and work
midair?”
The
answer is an eye-opener.
These
individuals appear to be floating because they’re falling through space.
If
you’ve ever experienced an amusement park ride where you enter a cabin that
gets dropped from a tall tower, then you know this feeling well.
The
same goes for the sensation you get when a roller coaster encounters a sudden
drop on the tracks.
Of
course, for us terrestrial-bound beings, this sense of weightlessness proves
very temporary.
FREEFALLING THROUGH SPACE
Why do
humans and objects fall at the same rate in space, creating the appearance of
weightlessness?
That’s
because they’re falling through a vacuum.
In a
vacuum, all objects plunge at the same rate. Gravity, not mass, dictates this
rate.
Things
operate differently on the Earth, however.
If
you’ve ever dropped a feather and a metal ball from a tower at the same height,
you already understand this.
The
ball will crash into the ground much faster than the feather. What gives?
On
Earth, air resistance alters the rate of descent for various objects. Removing
this resistance, however, permits the feather to fall at the same rate as the
ball.
Let’s
take the amusement park ride that we mentioned earlier.
Imagine
riding it again, only this time you have a quarter in your hand. If, during the
descent, you let go of the quarter what do you think will happen?
It‘ll
fall at the same rate as your body, giving the impression that it’s floating
directly in front of you.
The
same thing happens to all objects in space.
FALLING TOWARD AND AROUND THE EARTH
They
all descend at the same rate, and that’s why they appear to float.
The
gravitational pull of the Earth is not the sole force acting on these objects
and individuals, however.
The
space station is traveling at upwards of 17,500 miles per hour, moving at a
speed that matches the curve of the Earth’s surface.
As a
result, the space station is both moving towards the Earth and around it.
This
movement towards and around the Earth keeps
the space station from plummeting into the planet.
This
principle also explains why the Moon orbits the Earth instead of colliding with
it. In other words, the Moon is also falling around the Earth.
WHY MICROGRAVITY MATTERS
Organizations
such as NASA study microgravity.
Why? To
gain a better understanding of what happens to equipment and individuals in
space.
What do
we know about the effects of microgravity on the human body so far?
For
one, long-term exposure leads to weakened bones and muscle atrophy because
microgravity offers so little resistance.
Understanding
the negative physiological impacts of this environment will prove critical to
future space exploration. After all, astronauts must stay healthy and robust
despite extended journeys, say to Mars.
Besides
human beings, microgravity also has some interesting impacts on other natural
phenomena.
For
example, crystals grow better in space, and flames take on a round shape
because of the decreased pull of gravity.
Conducting
such experiments in space will help scientists to continue honing their
understanding of microgravity environments and their impacts on physical
objects.
By Engrid
Barnett, contributor for Ripleys.com
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