Transcript Energy Lecture

“EnergyTransformations”



Energy is a measure of the ability to do
work.
SI Unit for energy: Joule (J)
There are two main categories of energy,
nonmechanical and mechanical energy.
 Nonmechanical
energy is small
scale (meaning the
scale of atoms).

Examples of NME
include:
thermal/heat,
electromagnetic,
nuclear, electric,
sound, and
chemical.
Chemical Energy:


Energy associated with both the making
and breaking of chemical bonds.
Nuclear Energy:


Energy that binds the nucleus of an atom
together. Can be released through nuclear
fission or fusion.
Electromagnetic Energy:


Form of energy made from electrical and magnetic
waves and packets of energy called photons.
Sound Energy:


Energy that travels in waves by vibrating
molecules in a medium.
Electrical Energy:


Energy associated with the flow of
electrons through wires or other
conducting materials.
Thermal/Heat
Energy:

Energy associated
with the average
kinetic energy of
atoms or
molecules.





Heat energy can be
transferred in
three ways:
Conduction
Convection
Radiation
 Mechanical
energy is composed of 2 types:
GPE (gravitational potential energy) and KE
(kinetic energy). ME is large scale meaning
you can SEE it.

Potential Energy is the
stored energy resulting from
the relative positions of
objects in a system.
There are two types:
Elastic Potential Energy
Gravitational Potential Energy
GPE (J) = mass (kg) x free-fall acceleration (9.8 m/s2) x height (m)
GPE = mgh
g = 9.8 m/s2
GPE
(m x g x h)

Kinetic Energy is
the energy of a
moving object
due to its motion.
Kinetic Energy (J) = ½ x mass (kg) x speed2 ([m/s]2)
KE = 1/2mv2
KE
(.5 x m x v2)
KE’s
equation shows us
that two main things
affect KE:
Mass
Speed

Mass: As an objects mass
increases, so does its KE.
I have a BIG
kinetic
energy when
I’m moving!
I have a
SMALL kinetic
energy when
I’m moving!
Speed:
As an object’s speed
increases, so does its KE. So as
any object falls, its KE increases.
Penny off of the Empire State Building
Calculate the gravitational potential energy of a 1200 kg
car at the top of a hill that is 42 m high.
GPE =
?
m=
1200 kg
GPE
g=
9.8 m/s2
h=
(m x g x h)
42 m
GPE = m x g x h
GPE = 1200 x 9.8 x 42
GPE = 493,920 J

If a penny is sitting at the edge of a building with a mass of
0.0005 kg and a gravitational potential energy of 0.147,
How tall is the building?
GPE =
0.147 J
m=
0.0005
GPE
g=
9.8 m/s2
(m x g x h)
h=
?
h = GPE / (m x g)
h = 0.147 / (0.0005 x 9.8)
h = 0.147 / (0.0049)
h = 30 m

What is the kinetic energy of a 44 kg cheetah
running at 31 m/s?

KE = ?

m=
44 kg
KE

v=
31 m/s
(.5 x m x v2)

v2 =
961 (m/s)2
KE = .5 x m x v2
KE = (.5)(44)(961)
KE = 21,142 J
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m
m
m
m
=
=
=
=
A bowling ball traveling 2.0 m/s has 16 J of kinetic
energy. What is the mass of the bowling ball in
kilograms?
m=?
KE =
16 J
KE
v=
2 m/s
(.5 x m x v2)
v2 =
4 (m/s)2
KE / (.5 x v2)
16 / (.5 x 4)
16 / (2)
8 kg
A 35 kg child has 190 J of kinetic energy after he
sleds down a hill. What is the child’s speed at the
bottom of the hill?

v=?

v2 = ?
KE =
KE
190 J
m=
(.5 x m x v2)
35 kg
v2 = KE / (.5 x m)
v2 = 190 / (.5 x 35)
v2 = 190 / (17.5)
v2 = √10.9
v = 3.3 m/s


The Law of
Conservation of Energy
says that energy cannot
be created or destroyed,
it can only change forms.

A perpetual motion machine is a machine designed
to keep going forever without any input of energy.
This means ALL of the energy put into the machine stays
in the machine perpetually (forever).
 It’s a perfect model of the law of conservation except it’s

Potential energy can be transformed into
kinetic energy and vice versa.




Example:
As a roller coaster is pulled up to the top
of the first hill, the mechanical energy is
stored as gravitational potential energy.
As it goes down the other side of the hill,
the roller coaster picks up speed,
transforming the potential energy to
kinetic energy.
Roller Coaster Physics Design Your Own Roller Coaster