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Unit 2: Motion Page 11
much gravity pulling on them. the more inertia it has. I like to
Things in orbit (the moon, think of inertia as a mule. It is
satellites, etc.) do feel the pull of often very hard to get a mule to
Earth’s gravity but they are moving move, and once you do get him
fast enough to keep falling around moving it is very difficult to get
the Earth and not into the Earth. him to stop or to change
directions!
Now imagine Newton sitting there
in 1700, he has never seen a Quick quiz! Which has more
frictionless place or a place with no inertia, a ping-pong ball or a train?
gravity. He’s never seen the If you said “train” you’re right. It is
pictures from the space shuttle of very easy to get a ping-pong ball
things floating around. No one’s to move and it is very easy to get
been to the moon yet. For him to it to stop. A train, on the other
“see” the reality that in such places hand, is quite difficult to move or
things would never stop moving is stop!
pure genius.
Newton's Second Law
Aristotle said the natural state for
most objects was to be at rest. Newton’s Second Law is one of the
Newton, without ever seeing any toughest of the laws to understand
evidence to the contrary, said the but it is very powerful. In its
natural state for a moving object mathematical form, it is so simple,
was to continue moving. When you it’s elegant. Mathematically it is
can see through what everybody F=ma or Force = Mass x
has believed to be true for Acceleration. An easy way to
centuries you are a true genius (or remember that is to think of your
out of your head!). mother trying to get you out of bed
in the morning. Force equals MA!
Why is it hard to move a (Did I mention physics jokes are
bowling ball? There is a term in usually pretty bad?)
physics that really kind of
encompasses Newton’s first law, In English, Newton’s Second Law
and that is inertia. Inertia is a can be stated a few different ways:
quality of an object that The more mass something has
determines how difficult it is to get and/or the faster it’s accelerating,
that object to move, to stop the more force it will put on
moving, or to change directions. whatever it hits. F=ma For
Generally, the heavier an object is, example, a car colliding at 30 mph
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