Download Chapter 4 * Energy

How are Energy, Work, and Power
Related?
 What are the two main types of energy?

Energy: the ability to do work or cause
change
 Kinetic energy: the energy of an object
in motion
 Potential energy: the energy an object
has due to its position or shape

Gravitational potential energy: PE
related to an object’s height
 Elastic potential energy: PE associated
with an object that can be compressed
or stretched.


Since energy is similar to work, it can be
substituted in the following formula:
› Power = Work / time
› Power = Energy / time

The two basic types of energy are kinetic
and potential.

Kinetic energy (of motion) depends on
an object’s speed and mass.
› The faster the object moves, the greater the
KE.
› The more mass an object has, the greater
the KE.

Kinetic Energy can be found by the
following formula:
› KE = (1/2)(m)(s2)
› KE = (0.5)(m)(s2)

Notice that speed is squared. This means
that if the mass is doubled, KE is doubled.
If the speed is doubled, the KE is
quadrupled.

The gravitational PE of an object is equal
to the work done to lift the object to that
height.
› GPE = (weight)(height)

When an object is stretched (like a spring
or a rubber band), it has greater elastic
potential energy.

Question: How does mass affect how many times a ball
will bounce before stopping?

Hypothesis: When the mass of the ball (increases,
decreases) ____________________ then the number of
bounces will (increase, decrease) _________________
because ____________________.

Materials:
›
›
›
›
›
Meter stick
golf ball
Tennis ball
Ping pong ball
Marble

1.
2.
3.
4.
5.
Procedures:
Have one member of the group hold the meter stick
upright with the zero mark on the table.
Have a second member of the group drop the tennis ball
from the top of the meter stick (100cm mark) in such a
way that it does not touch the meter stick on the way
down.
Have a third member of the group count the number of
bounces. The number of bounces should be called out to
the fourth member of the group, who should record it in
the data table. Repeat for 4 additional trials.
Repeat steps 1, 2, and 3 with each of the other balls until
all balls have been tested.
On the graphs, label the axis, and plot the average
number of bounces for each ball.

Data Analysis
Type of Ball
Golf Ball
Rubber Ball
Air-filled Ball
Sponge Ball
T
1
Number of Bounces
T
T
T
2
3
4
T
5
Average #
Bounces


1.
2.
3.
4.
Make the graph AND answer the following questions
on a separate sheet of paper.
Answer the questions using the following key terms.
(gravitational potential energy; kinetic energy;
energy conversion, mechanical energy, mass)
Which ball retained the greatest percentage of its
kinetic energy on each bounce? Why?
What can't a ball bounce higher that the height
from which it is dropped?
The law of conservation states that:
Explain how the law of conservation applies to this
experiment?
How can you find an object’s
mechanical energy?
 What are other forms of energy?

Mechanical energy: the form of energy
associated with the motion position or
shape of an object
 Nuclear energy: type of potential
energy; stored in the nucleus of an atom
and released during a nuclear reaction.
 Thermal energy: the total kinetic and
potential energy of the particles in an
object.

Electrical energy: the energy of electric
charges.
 Electromagnetic energy: a form of
energy that ravels through space in
waves.
 Chemical energy: potential energy
stored in chemical bonds.

ME (mechanical energy) is a
combination of KE and PE.
 It can be calculated by adding the two
together;

› ME = KE + PE
Objects with ME can do work.
 The more ME an object has, the more
work it can do.

 All
objects are made of atoms and all
atoms have a nucleus.
 Nuclear fission occurs when a nucleus
is split.
› Nuclear plants use this to create
electricity
 Nuclear
fusion occurs when multiple
nuclei join together.
The higher the temperature of an object,
the greater its thermal energy.
 The faster the particles move, the more KE
they have, and the greater their thermal
temp.


If electricity is moving, like lightning, then it is
KE; if it is still, like static electricity, then it is
PE.

Chemical bonds exist in food particles; they
hold atoms together.

When chem bonds are broken, energy is
released.
How are different forms of energy
related?
 What is the law of conservation of
energy?

Energy transformation: a change from
one form of energy to another.
 Law of conservation of energy: when
one form of energy is transformed into
another, no energy is lost in the process;
energy cannot be created or destroyed.


All forms of energy can be transformed
into other forms of energy.

Single transformation examples:
› Electrical energy turned into thermal energy
to toast bread
› Chemical energy transformed into ATP
(usable energy) in muscles

Multiple transformation example:
› Lighting a match takes several
transformations; it involves ME, thermal
energy, chemical energy, and
electromagnetic energy that we can see.

KE and PE transformations:
› Bouncing a ball – when the ball hits the
ground and reaches the top of its bounce it
has PE; when it is falling down and bouncing
up it is gaining KE.
› Pendulum – at the top of its swing on either
side is when the object has its greatest PE; at
the middle of its swing is when it has its
greatest KE.

The total amount of energy is the same
before and after any transformation.

Whenever friction/air resistance is
present, some KE is changed into
thermal energy.
› Remember…machines cannot be 100%
efficient because of friction; work and
energy are equivalent.