Chapter 3 - Kawameeh Middle School

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S
Chapter 3
Lesson 1
Energy
S The ability of a system to do work.
Two types of energy:
• Kinetic Energy
• Potential Energy
States of Energy
All forms of energy can be in either of
two states:
What’s the difference?
S Kinetic Energy is
the energy of
MOTION
S Potential Energy
is STORED
energy.
Kinetic Energy – what does it
depend on?
The faster an object moves, the more kinetic energy
it has.
 The greater the mass of a moving object, the
more kinetic energy it has.
 Kinetic energy depends on both mass and velocity.

Calculating Kinetic Energy
KE  0.5  mass  velocity
2
What has a greater affect of kinetic energy, mass or
velocity? Why?
What is the unit for Kinetic
Energy?
S Unit: Joule
S Named after: James Prescott Joule
S He discovered the relationship between heat (energy)
and mechanical work which led to the law of
conservation of energy.
S How do we derive this unit?
S 1 Joule = 1kg ∙ m2/s2
S KE = ½ ∙ m(kg) ∙ v(m/s) 2
Some types of Potential Energy
include…

Gravitational potential energy
- stored energy due to an objects position
(height)
- depends on mass of the object and its distance
from earth.

Elastic potential energy - Stored energy due to
- Stored energy due to compression or expansion
of an elastic object
Calculating Potential Energy
PE  mass  gravity  height
S OR you could multiply weight (in Newton’s) by height

What unit do we use for
Potential Energy?
S Unit: Joule
S How do we derive this unit?
S 1 Joule = 1kg ∙ m2/s2
S PE = m(kg) ∙ g (m/s2 ) ∙ height (m)
1. You serve a volleyball with a mass of 2.1 kg. The ball leaves
your hand with a speed of 30 m/s. The ball has ___________
energy. Calculate it.
2. A baby carriage is sitting at the top of a hill that is 21 m
high. The carriage with the baby weighs 12 N. The carriage
has ____________ energy. Calculate it.
3. A car is traveling with a velocity of 40 m/s and has a mass
of 1120 kg. The car has ___________energy. Calculate it.
4. A cinder block is sitting on a platform 20 m high. It weighs
79 N. The block has _____________ energy. Calculate it.
5. A roller coaster is at the top of a 72 m hill and weighs 966
N. The coaster (at this moment) has ____________ energy.
Calculate it.
6. Two objects were lifted by a machine. One object had a mass of 2
kilograms, and was lifted at a speed of 2 m/sec. The other had a mass of
4 kilograms and was lifted at a rate of 3 m/sec.
a. Which object had more kinetic energy while it was being lifted?
b. Which object had more potential energy when it was lifted to a
distance of 10 meters? Show your
calculation.

As a
basketball
player throws
the ball into
the air,
various
energy
conversions
take place.
Lesson 2
Law of Conservation of Energy
S Energy can be neither created nor destroyed by
ordinary means.
transformed or transferred
one form to another.
S Energy can be
from
is the same before
and after any transformation or transfer.
S The total amount of
energy
Energy Transfer
S Energy TRANSFER is the passing of energy from
one object to another object.
Example: A cup of hot tea has
thermal energy. Some of this
thermal energy is transferred to the
particles in cold milk, in which
you put to make the coffee cooler.
Energy Transformation
S A change from one form of energy to another.
S Single Transformations
S Occur when one form of energy
into another to get work done.
needs to be transformed
S Multiple Transformations
S Occur when a series
of energy transformations are needed to
do work
Energy Transformation
S An objects energy can be:
1. All Kinetic Energy
2. All Potential Energy
3. A combination of both
increases and potential energy
decreases
S As velocity decreases kinetic energy decreases and potential
energy increases
WHAT IS THE TYPE OF RELATIONSHIP KE AND PE HAVE? INVERSE
S As velocity increases kinetic energy
Roller Coasters
Does energy get transferred or
transformed?
• As you move up to the first hill on a roller coaster the distance
between the coaster and the Earth increases, resulting in an increase
of Gravitational Potential Energy.
• At the top of the first hill you have the most Gravitational Potential
Energy
• As you begin your trip down the hill you increase your speed
resulting in a transformation from GPE to KE.
• At the bottom of the hill right before it goes back upward the
GPE is small, but the KE is Large.
• As it starts to move up the next hill or loop KE is transformed
back into GPE
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