Download Calculating Kinetic and Potential Energy

Unit 5
Relationships among forms of
energy
8th Grade Middle School science
Union township school district
S
Energy
S The ability of a system to do work.
Two types of energy:
• Kinetic Energy
• Potential Energy
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 due to an
objects position.
Kinetic Energy – what does it
depend on?



The faster an object moves (velocity) , 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.
Some types of kinetic energy
include…
S Electrical - The
energy that an electric current carries is
a form of kinetic energy.
S Radiant - the
energy carried by electromagnetic waves.
S Sound - energy
S Seismic - is
carried by sound waves
the energy transferred by waves moving
through the ground.
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
Practice Problem 1
S What is the Kinetic Energy of a 150 kg object that is
moving with a velocity of 15 m/s?
Practice Problem 2
S What is the Kinetic Energy of a 1200 kg object that is
moving with a velocity of 24 m/s?
Practice Problem 3
S What is the Kinetic Energy of a 478 kg object that is
moving with a velocity of 15 m/s?
Practice
S What is the Kinetic Energy of a 150 kg object that is
moving with a speed of 15 m/s?
S An object has a kinetic energy of 25 J and a mass of 34 kg,
how fast is the object moving?
S An object moving with a speed of 35 m/s and has a
kinetic energy of 1500 J, what is the mass of the object.
Potential Energy
S Stored energy that depends on the interaction of
objects, particles, or atoms.
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 compression or expansion
of an elastic object
Some types of Potential Energy
include…

Chemical energy - energy that is stored in and
released from the bonds between atoms.

Nuclear– energy stored in and released from the
nucleus of an atom.
Calculating Potential Energy
PE  mass gravity height
• If you are given Newton’s (N) that is the product of mass
and gravity.
• A Newton is a force
• Gravity (acceleration due to gravity) = 9.8m/s2 on Earth.

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 has a
mass of 5kg. 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.
A combination of Kinetic and
Potential Energy
S Thermal - The
sum of the kinetic energy and potential
energy of the particles that make up an object
S The motion of the particles PLUS the distance between the
particles.
S Mechanical - The
sum of potential energy and kinetic
energy in a system of objects.
S The motion of the object PLUS the objects position

As a
basketball
player throws
the ball into
the air,
various
energy
conversions
take place.
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.
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
Identify the following:
Greatest Potential
Greatest Kinetic
Least Potential
Least Kinetic
Area where both kinetic and potential energy is almost
even.