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Unit 5: Energy (Part 2) Page 9
Joules of kinetic energy (kinetic Gravitational Potential
energy is the energy of motion).
Energy
What’s meant by kinetic energy is
that when it hits something, it can There’s one specific type of
do that much work on whatever is potential energy that’s worth
hit. spending some more time on.
That’s gravitational potential
Soooo, back to the arrow, if the energy. Gravitational potential
arrow hits that apple it can exert energy is the energy something
10 Joules of energy on that apple. has due to gravity. This is the
It takes about 1 Newton of force to physics version of “what goes up,
move that apple so the arrow can must come down”.
move the apple 10 meters. One
Joule equals one Newton x one If a ball is sitting on top of a book
meter so 10 Joules would equal shelf, it has the potential to fall off.
one Newton x 10 meters. If the ball were to fall off the
bookshelf it would potentially hit
It could also exert a force of 10 the floor with a certain amount of
Newton's over one meter or any Joules of energy.
other mathematical calculation
you’d like to play with there. The formula for this is potential
energy = mass x gravity x height,
(This, by the way, is completely or PE=mgh.
hypothetical. With the apple
example we are conveniently Mass is the mass of the object,
ignoring a bunch of stuff like the Gravity is the gravitational
2
fact that the arrow would actually constant 10 m/s , and height is
pierce the apple, and that there’s how high the object is above the
friction, heat, sound, and a variety ground.
of other forces and energies that
would take place here.) The gravitational constant is how
fast gravity accelerates things and
2
The formula for kinetic energy is we’ve generally been using 32 ft/s
2
1/2 mass x velocity or KE = 1/2 . However, since we’re calculating
2
mv . Joules here, we need to use metric
measurements. In metric the
2
We’ll be doing lots of experiments gravitation constant is 9.8 m/s . I
2
to make this clearer. tend to round that up to 10 m/s to
make the math a little simpler. So,
let’s say that a 1 kg ball is sitting
on a 2 meter (about 6 feet) tall
bookshelf.
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