The Truth About Astronauts “Floating” in Space

Did you know that in my teachings with students and workshops for teachers I find that students and adults answer many of the same science questions wrong?  I see this year after year when I discuss certain subjects with my students.  In fact, before I wrote the first of my two books, my idea was to make a video covering this topic.

Let us begin with, what I find, is the most common science misconception. This is how I would ask it in class or at a workshop.

QUESTION:  Why do the space shuttle astronauts seem to float in space?

The common answer is a misconception:  There is no gravity in outer space.

Follow up question: What keeps the moon in orbit around the earth?

Not a misconception:  gravity.

Follow up statement: You mean to tell me that a shuttle astronaut who is roughly 100  miles
above the earth has no gravity on them. While the moon, which is one fourth the earth’s size and
about 240,000 miles away, is kept in orbit by the gravity of the earth?  When you think about that,
it does not make any sense.

The real answer: The shuttle astronauts are in free fall along with the space shuttle in an orbit around
the earth. An example of this was in the movie Apollo 13.  To simulate the astronauts in space, they
flew in an airplane called the “Vomit Comet” at a very rapid rate of descent.  When the plane and
“astronauts” descended at a steep enough angle, they were in free fall and the plane and “astronauts”
fell at the same rate.  This made it appear that they were “floating”.  Using this plane they could
simulate weightlessness for about 30 seconds.  Then the plane had to level off for crash avoidance.
This was the result of the force fo gravity.  An explanation is forthcoming but first some
needed information.

The first premise that astronauts seem to float because there is no gravity is false.  First of all, it is
impossible to float in space because to float requires something to float on.  Boats float on water and
helium balloons float in air but outer space contains so little matter there is basically nothing to float on.

Why people are fooled: The term zero G.  It does not mean no gravity.  It refers to no net force.
For example, if we add a + 4 and a -4 we get zero. That does not mean we started out with nothing,
we just ended up with nothing.  If we made $500 but had to pay $500 in taxes, our net income was
zero!  We made some money, we just didn’t end up with any.

In the case of the astronauts, it is not +500 and -500 but the force of
gravity and inertia that balance out to obtain no net force. 

Almost everyone knows that gravity is a pulling force.  It attracts any two objects.  The
larger the object, the more pull that it has.  That is why the astronauts on
the moon in 1969 and in the early 70’s seemed to hop when they walked, the
moon is smaller and has one sixth the gravity of the earth.  Gravity also
depends upon the distance between the two objects.  The moon pulls more on
our oceans to cause tides than does the sun, which is much larger, because it
is closer to the earth’s oceans.

Inertia is a tendency that, when talking about spacecraft, tries to keep objects
going in a straight line.  That is what we will concentrate on about inertia
here.  (Just for your information, inertia tries to keep moving things
moving.  An example is when we are riding a bike and quit pedaling, inertia
tries to keep the bike moving anyway unless a force like the brakes stop it.
Friction with the air and road are also forces that will slow the bike.
Inertia also tries to keep non moving objects non moving.  Pushing a car by
hand from a dead stop is difficult because inertia tries to make it stay put.
However, once you get the car moving, it moves quite easily because of
inertia but would then be difficult to stop by hand.  To summarize inertia:
it tries to keep things the way they are unless an outside force comes along
to change things.

How inertia and gravity work on the space shuttle: Gravity tries to pull
the space shuttle towards the earth,  the shuttle moves forward in a straight line because of inertia.. 

I am going to describe this process with the following example:

Imagine a little league baseball player hitting a home run.  The ball flies
out caused by the force of the bat (inertia) but it is brought to earth by
gravity and slowed down in its flight by friction with the air.

Further, imagine Derek Jeter hitting a home run.  The ball travels farther
and higher (more inertia) but it is still slowed by friction and pulled down
by gravity.  It just takes longer for these things to happen because Derek
Jeter provided more initial force than the little leaguer.

Now imagine one step further.  The ball was hit with enough force to so that
its falling path matches the curvature of the earth.  Since friction is
almost nonexistent outside our atmosphere, there is very little to slow it
down, the ball is able to maintain its speed and goes into orbit around the
earth.  This is called “free fall” and you probably have experienced it while
going downhill on a roller coaster.  It is that feeling when we seem to come
off of our seat and our stomach seems to rise.  Did you ever notice that
“floating” feeling when going down that hill?

Author’s note: Eventually the small amount of friction in space would make a
difference, there is just not enough in a normal shuttle flight.  That is why
we sometimes hear about satellites coming out of orbit and burning up in the
atmosphere after being in orbit for a long time. The only way to keep them in
their orbit would be to fire the rocket engine in a proper sequence to keep
its rate of speed.
An experiment that will demonstrate the forces 
is to get a weight tied to a string.  Then spin the string above
your head.  We have all done something like this sometime.  What happens when
you let go of the string?  It starts to fly in a straight line (inertia) but
will quickly go in a curve because of gravity and air friction.  What happens
if you don’t spin it fast enough?  It starts to fall (gravity). Satellites
and the space shuttle are affected by the same forces.

How we end up with zero G: zero G is a way of saying that forces are
balanced - no net force.  The shape of an orbit is made by a balance of
gravity and tendecy to go straight (inertia).  NASA people can’t control the force of gravity but they
can control the speed of the shuttle which causes the forward force.
Mathematically, the NASA people figure a speed for the weight of the shuttle
so that when gravity is figured in, the orbit of the shuttle somewhat matches
the curvature of the earth.

Imagine a line going across like this  ——>.   That is inertia.  Imagine a
line going straight down, that is gravity.  The shape of an orbit is neither
one of those lines but a curve between the two lines - zero G, the balance
between inertia and gravity.

Here is a visual aid you can easily make to describe what we’ve talked about.

1.  On a blank sheet of paper, draw a circle to be the earth.

2.  Make a mark above the 12 o’clock position.   Above the mark draw an arrow
pointing downward toward the earth.  This represents gravity.

3.  At the beginning of the line you used to draw the downward arrow,  draw
another arrow pointing to the right as you see in the above paragraph.

4.  Make a dot on the circle at 3 o’clock.  Turn the paper one quarter turn
counterclockwise so the dot at three o’clock is on top where 12 o’clock
was.  Draw the same arrows in the same position as you did before.

5.  Make a dot where 6 o’clock would be on the face of the circle.  Turn it
up to the top as you’ve already done and draw the arrows again.

6.  Complete the diagram by doing the same thing at nine o’clock and draw the
same arrows.

7.  Turn the paper right side up as when you started.  You now see the forces
of inertia and gravity as they act upon the space shuttle in orbit on
different parts of the earth.

8.  From your first two arrows above 12 o’clock, draw a curved line between
the arrows to show an orbit all the way around your “earth”.  This is the
balance between inertia and gravity.

Finally, if you are wondering how much gravity is up there in the space
shuttle it is about 90% of that on earth.  NASA calls it microgravity.  That  is misleading too because micro means small.