Chapter
4
Energy
Notes
Section 4.1
The Nature of Energy
A. Energy is the ability to cause change.
1. Kinetic energy – energy in the form of
motion
___________
What does Kinetic mean ?
xbox kinect , kinesthetic, telekinesis
a. The amount of kinetic energy an object has
depends on its mass and its ________________
speed
b. kinetic energy = 1 /2 mass x speed 2
KE = 1/2mv2
KE = .5 X kg x v 2
c. Joule - the SI unit used to measure energy
Turn over your note page & copy these examples down
Title “Kinetic Math Problems”
Formula KE = 1/2mv2
1. What is the KE of a 44kg cheetah running at 31 m/s?
M
V
KE = ?
M = 44 kg
V = 31 m/s
KE = .5 x 44 x 31 2
In the calculator always do the squaring first …… 31 x 31
= .5 x 44 x 961
KE =
21,142 J
WRITE THIS DOWN ON THE BACK PAGE OF YOUR NOTES
2.Calculate the kinetic energy of a 1500 kg
car moving at a speed of 18 m/s ? M
V
KE = 1/2 mv2
KE = ?
M = 1500 kg
V = 18 m/s
KE = .5 x 1500 x 18 2
In the calculator always do the squaring first …… 18 x 18
= .5 x 1500 x 324
KE =
243, 000 J
2. Potential energy – energy stored in a motionless,
object, giving it the potential to cause change
a. Kinetic energy can become potential energy.
b. Potential energy can become kinetic energy.
Example:
• * A ball goes up with
kinetic energy, loses it,
gains potential energy,
slows down and falls,
gains kinetic energy.
3. Elastic potential energy – energy stored by things that stretch
or compress Example – spring
4. Chemical potential energy – energy stored in chemical bonds
between atoms. Example – converting food into energy
5. Gravitational potential energy – energy stored by things
that are above Earth.
a. The amount of gravitational potential energy
an object has depends on its mass, the
acceleration due to gravity, and its height
above ground.
b. Gravitational potential energy = mass in
kilograms x 9.8 m/s2 x height in meters or = mgh
Turn back of your notes & write down this example
M
h
1. 30 kg rock climber is at a point 20 m above the
base of the cliff? Solve PE?
FORMULA :
PE = mgh
m = mass
m=
g=
g = 9.8 m/s2
30 kg
____________
2
9.8
m/s
_________(always this number) ___
20 m
h = ____________
5880 J
PE = ____________
h = height
PE = 30 x 9.8 x 20
= 5880 J
Turn back of your notes & write down this example
M
2. What is the kinetic energy of a 44 kg cheetah
running at 31 m/s. KE = 1/2mv2
V
M = __________________
44 kg
31 m/s
V = __________________
21142 J
KE = _________________
= .5 x 44 x 31 2
= .5 x 44 x 961
OPTIONAL: To write down on the back of your notes
• How much kinetic energy does an object have if it’s
mass is 5.0 kg and a speed of 4.0 m/s?
M
V
KE = ½ mv2
= .5 x 5 x 4 2
=. 5 x 5 x 16
5.0 kg
M = __________
4.0 m/s
V = __________
40 J
KE = ____________
= 40 J