1. Gravity: the
phenomenon
that keeps
our feet on
the ground:
By Moira Whitehouse PhD

2. Gravity is a force.
Gravity is a force that pulls.
Every object has gravity.
So every object pulls on every other
object.
The more mass an object has, the harder
it pulls.

3. We will use two hypothetical planets for our
example. Both the blue and green planets
are pulling on each other.
Which one pulls harder?

4. This should help us see that the more mass
an object has the stronger its gravity.
Moon Earth
The Earth obviously has more mass than
But the Moon’s gravity is also pulling on
the Moon and it pulls harder.
the Earth. So hard that the oceans swell
So much harder that theever it passes. in an
toward the Moon where Moon is held We
call this high tide. Earth as though by some
orbit around the
magically strong string.

5. Let’s think about gravity on our favorite little
planet, Earth.

6. Gravity on Earth pulls everything toward
its center.

7. That’s why there is
no top or bottom
and no one falls
off.

8. If you dug a hole
right through the
Earth and fell in,
how far would
you fall?

9. You’d fall into the hole and shoot right past
the center because you would be going so
fast. As soon as you passed it, you
would be pulled
back towards the
center. So you
would bounce back
and forth like a
bungie jumper till
you finally stopped
at the center.

10. On Earth it appears that not everything falls
to the ground at the same rate.
It seems to us that things with less
mass or weight e.g. feathers fall
slower than things with more mass
or weight e.g. rocks.
This is a misconception.
As demonstrated by Galileo in the 1500’s, all
objects in a vacuum, fall at the same rate
regardless of mass.
Lighter objects on Earth fall slower due to
our atmosphere which slows their descent.

11. On the Moon, an astronaut dropped a
feather and a hammer.
Since there is no atmosphere on the
Moon the feather and the hammer hit
the ground at the same time.

12. Demo dropping book and paper.

13. The weight of an object is a measure of
how hard gravity pulls on it.
However, the amount of gravity on each
planet differs. The Moon has only one-sixth
as much gravity as the earth. Consequently,
on the moon you would weigh only one-
sixth of what you weigh on Earth.

14. This boy weighs
60 pounds on
Earth.

15. On the Moon he
would only weigh
10 pounds.

16. Since each planet has a
different amount of
gravity, this boy’s
weight would change
each time he went to
another planet.

21. On Jupiter,
this would be
like carrying
an extra 100
pounds
around on
your back all
day.

22. The farther an object is from the center of
a planet, the weaker the force of gravity.
So, would this apple weigh more in some
place like Death Valley or on top of a very
high mountain?

23. Weight of a one pound apple heading out
to space.
Apple Apple Apple Apple
weighs weighs weighs weighs
1 pound 1/4 pound 1/9 pound 1/16 pound
here here here here

24. In a spaceship like the shuttle, you would be
weightless. However this is not because
you are so far from Earth that there is no
gravity. It is because the spaceship, being
pulled by gravity, is always falling from
beneath you.

25. Both of these men are weightless, still they are
both being pulled by gravity. They have weight
only when gravity pushes them against
something like the floor or a scale.

26. What causes gravity?
Even the great At his time
Sir Isaac Newton and still
couldn’t answer today, what
that one. causes gravity
is a mystery.
But it is a force that effects everything in
the universe.