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Hi, my name is Bernie Horvath and I am the author
of The Home and School Science Activity Book.
My goal today is to straighten out a common science
misconception.
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?
Not a misconception: gravity.
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 two forces, gravity and inertia. 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 forces
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 force 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, while inertia tries to move the
shuttle
forward in a straight line. 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 Mark McGuire 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
Mark
McGuire 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 inertia.
An experiment that will demonstrate the forces of gravity, inertia
and
friction 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 (inertia).
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 inertia. NASA people can't control the force of gravity
but they
can control the speed of the shuttle which causes the forward force,
inertia.
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 at 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.
COOL
LINKS TO SEARCH OUT!
KIDSCIENCE-
A
must see site- lots of activities and fun!
EARTH
BALLOON - A GRAND earth awareness program.
|
See how many words you can make out of the three words below. Each word must be at least three letters. The number of words is in parenthesis after the word. Good Luck! 1. PLANT (13) 2. FORCE (7) 3. HUMANS (15) Answers are at the bottom of this page. |
Look at the images above. Do you see grey circles at the intersections of the white lines on the diagram on the left? The strong dark and light contrast at the intersections causes the four corners to extend their color into the white area. On the diagram on the right, do you see pink circles at the intersection of the red lines? Keep looking at it and you will see it!
1. Plant (13)- plan,plat,tan,tap,alp,ant,apt,lap,nap,pal,pan,pant,pat
2. Force (7)- core,for,fore,foe,fro,ore,roe
3. Humans (15) - ash,ham,hams,has,hum,hums,sham,human,man,mans,mash,mush,shun,sum,sun
Enjoy!
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