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Energy
What you need to know!
• Students know waves (i.e., sound, seismic,
electromagnetic) have energy that can be transferred
when the waves interact with matter. E/S
• Students know energy forms can be converted. E/S
• Students know nuclear reactions convert a relatively
small amount of material into a large amount of
energy. I/S
• Students know characteristics, applications and
impacts of radioactivity. E/S
• Students know the relationship between heat and
temperature. I/S
• Students know electricity is transferred from
generating sources for consumption and practical
uses. I/S
Figure 1. A schematic of the many connections within energy (from
http://hyperphysics.phy-astr.gsu.edu/hbase/enecon.html).
What is Energy
• Energy is the capacity to produce physical
changes.
– The word capacity is important because
change may or may not actually be occurring
(i.e., energy can be thought of as being
“stored” in some situations).
What does energy do?
• Energy causes matter to move.
• Physical change is often equated with
terms: work, heat, electromagnetic
radiation.
Energy
• Most important to
remember is that
ENERGY IS NOT
CREATED OR
DESTROYED.
Energy is only
transferred from place
to place.
Energy is typically stored as:
• Potential
– Storage of energy due
to:
• Position
• Chemical composition
• Kinetic
– Storage of energy in
due to:
• Motion
Transfer of energy
• In the diagram below, the amount of potential
energy (the left picture) must have been fully
transferred to the motion of the ram just before it
strikes the nail.
• The motion of the ram (shown in the middle
picture) is then transferred to the nail causing it
to move a distance. Where does the energy go
after it drove the nail?
Was the energy destroyed?
• NO! The original amount of energy from the first
picture will ultimately be transferred into the
environment. When the ram hits the nail the
nail will move. In addition to the movement of
the nail, sound and heat will also be produced.
Energy as Work
• Work is the force required to move
material a distance. But change
mechanisms associated with energy
include not only work, but also heat and
electromagnetic radiation.
Energy as Heat
• Energy can be added or removed from a system
through the process of heating.
• Most often the direct result of adding heat to a
material is an increase in the temperature of the
material.
• If heating a material doesn’t cause it’s
temperature to change then the material is
changing phases.
• Energy can be added or removed to cause a
phase change.
Heating Curve
Energy as Heat
• There are three mechanisms in which heat
transfer can occur.
– Radiation - transfer of energy (including heat)
through electromagnetic waves.
– Convection - occurs by currents through a
fluid. Fluids may be defined as a liquid or gas.
Convection cells are caused by heating and
changes in density.
– Conduction - occurs within materials and
between materials that are in direct contact.
Energy as Waves
• Mechanical Waves
– require a medium
(solid, liquid, or gas) to
transmit its energy.
– Two types:
• Longitudinal
• Transverse
• Electromagnetic Waves
– No medium required to
transfer energy
– Typically referred to as
light (not just the visible
spectrum).
– All EM waves are
transverse.
ALL waves transfer energy by interacting with
particles. The interaction causes particles to vibrate.
Mechanical Waves
Sound is a longitudinal
mechanical wave.
Electromagnetic Waves
• More energy is carried by the EM wave as you increase
frequency (move from left to right in the diagram).
– If visible light’s frequency were increased, what type of waves
could result?
Energy as Nuclear Reactions
• Fission
– Atom is split into one
or more progeny
products
– Some of the nuclear
mass is converted to
energy.
– Nuclear power plants
sought to use the
fission reaction to
generate the heat
needed to drive
turbines in a process
to generate electricity.
• Fusion
– Two or more lighter
elements combine to
form a heavier atom.
– Some of the nuclear
mass is converted to
energy.
– Occurs in a star’s core
and is responsible for
all of the energy
radiating out of stars.
Nuclear Reactions
Nuclear Reactions
Fusion
Energy Question
Which of the following is NOT a
characteristic of mechanical waves?
a. They consist of disturbances or
oscillations of a medium.
b. They transport energy.
c. They travel through vacuums, as well
as gases, liquids, and solids.
d. They are created by a vibrating source.
Energy Question
In order for a medium to be able to
support a wave, the particles in the
wave must be
a. frictionless.
b. isolated from one another.
c. able to interact.
d. very light.
Energy Question
Using the figure below, which of the following
statements is correct?
a. The total energy in the system is 100,000 J.
b. The total energy in the system is 50,000 J.
c. The total energy in the system is 0 J.
d. The total energy at the end is half as much as it was in
the beginning.
Energy Question
A ball falls from a height of 20 meters. As the ball is
free falling towards the ground (and ignoring air
resistance)
a. The ball does not have any potential energy and is
gaining kinetic energy with the total energy increasing.
b. The ball’s potential energy increases and its kinetic
energy decreases with the total energy remaining the
same.
c. The ball’s potential energy decreases more rapidly than
the kinetic energy with the total energy decreasing.
d. The ball is losing potential energy and gaining kinetic
energy with the total energy remaining the same.
Energy Question
Energy is created as the result of which
activity?
a. Burning gasoline in an internal
combustion engine.
b. Damming a river for hydroelectric power.
c. Rolling a marble down an incline plane.
d. Energy cannot be created.
Energy Question
If you mix 50ml of water at 100°C with
50ml of water at 0°C what will be the
resulting temperature of the 100ml of
water?
a. 100°C
b. 75°C
c. 50°C
d. 25°C
Energy Question
The three basic mechanisms for heat
transfer are conduction, convection
and radiation. Which of these three
types require the direct contact of
material?
a. convection and radiation
b. conduction only
c. radiation and conduction
d. radiation only
Energy Question
Nuclear fusion reactions
a. involve electrons of one atom reacting with the
electrons of another atom.
b. occur commonly on Earth through naturally
occurring radioactive materials.
c. cause large atoms to divide into smaller atoms
releasing large amounts of energy.
d. cause smaller atoms to combine into larger
atoms releasing large amounts of energy.