The Manga Guide to Physics

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

didn’t 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...

...

Don’t ever play such

a childish practical

joke on me again!

I won’t 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