The Conservation of Mechanical Energy
Transforming Energy
So, now we know
how kinetic energy
and potential
energy can be
transformed into
each other.
Yes
energy must be
conserved, just
like momentum.
Let’s reconfirm
that law using
the example of
your high jump.
When you jump o
the ground, your
muscles work to
give kinetic energy
to your body.
184 Chapter 4 Energy
After leaving the
ground, the higher you
are, the le kinetic
energy you have.
You have no kinetic
energy at the peak
of your jump, since
your velocity is
zero.
At this time, your
potential energy is
at its maximum!
You s, this
is how kinetic
energy changes to
potential energy.
After faing from
yourpeak position, your
potential energy is
converted into kinetic
energy. During your landing,
the mat does negative work
on your body, as your
kinetic energy decreases.
Transforming Energy 185
Potential energy
can take other
forms besides
gravitational.
I have something
just for the
oasion. Let’s
try another
experiment.
What’s this
one going
tobe?
Here you
are.
It’s a
present
for you.
Reay?
For me?
Pre the
buon to open
the box.
Wow, you
didnt have
to...
P
o
p
Click
Pit-a-pat
186 Chapter 4 Energy
This toy worm
has a spring
inside.
While it is in the
box, the spring is
contracted, storing
potential energy.
When the lid is
removed, the potential
energy becomes
kinetic energy.
As a result
the toy has a
velocity! In
this case, into
yourface.
Conservation of
Mechanical Energy
Boy, I never thought
that an athlete like you
would be...
Potential energy
is present
Potential energy
becomes kinetic
energy
Velocity
Ack!
Transforming Energy 187
so scared by
a lile toy
worm.
I’m soy.
Not to change
the subject, but
I’m wondering if
we can talk about
the conversion of
kinetic and potential
energy in more
detail...
...
Dont ever play such
a childish practical
joke on me again!
I wont dare!
Ipromise!
Okay, fine. So?
Our earlier high-
jump example
involved the
human body, which
complicates
maers.
So let’s lk at a
simpler example:
aba thrown
intothe air.
Harumph.
Relieved
188 Chapter 4 Energy

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