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Activity 1
Goals
Exploring Energy Resource Concepts
Think about It
In this activity you will:
• Investigate heat transfer by the
processes of conduction,
convection, and radiation.
• Investigate the conversion of
mechanical energy into heat.
• Learn about the Second Law of
Thermodynamics and how it
relates to the generation of
electricity.
A car moving along a mountain road has energy. It has energy
due to its motion (kinetic energy), energy due to its position
in a gravity field (potential energy), and energy stored as
fuel in its gas tank (chemical energy).
• Classify each item below as having kinetic energy, potential
energy, or chemical energy:
a)
b)
c)
d)
e)
f)
g)
a rock balanced at the edge of a cliff
a piece of coal
a landslide
a roller-coaster car
a diver on a 10-m platform
a car battery
tides
What do you think? Record your ideas in your EarthComm
notebook. Be prepared to discuss your responses with your
small group and the class.
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Activity 1 Exploring Energy Resource Concepts
Investigate
b) With the approval of your teacher,
carry out your experiment, and
record your observations.
Energy can neither be created nor
destroyed (except in nuclear reactions),
but it can be changed from one form
into another. The following activities
will help you to explore basic concepts
that govern the use of energy.
3. Five minutes after you fill the cup,
place your hand around each of the
cups.
a) Which one feels hotter? Why?
Part A: Heat Transfer
Station 1
1. Put your hand close to a 100-W light
bulb and notice the heating that
occurs in your hand. This is similar
to the heat generated from direct
sunlight.
Be sure your teacher approves your design before
you begin. The water should not be hot enough to scald.
Wipe up spills immediately. Use alcohol thermometers only.
Station 3
1. Set up two solar cookers as shown
in the diagrams below. One is a
standard solar cooker and the other
is an identical solar cooker inside an
insulated box.
a) Describe what happens to the
temperature of your hand as you
move it slowly toward and away
from the bulb.
b) Hold a piece of paper between
your hand and the light bulb.
Describe and explain the change
in temperature of your hand.
a) What differences do you expect in
the temperature inside the two
solar cookers over time? Write
down your hypothesis in your
notebook.
c) Compare and explain the
temperature difference of your
hand when you hold it above the
light bulb versus holding it near
the side of the bulb.
insulated box
Be careful not to touch the hot bulb.
Station 2
1. Which cup will keep the water hot
for a longer amount of time, a metal
cup or a Styrofoam® cup? Why?
2. Design an investigation to test your
hypothesis. Your design should include
a plan to measure the temperature in
each solar cooker and to record data
every minute for at least 25 minutes.
a) Write down your hypothesis.
2. Design an experiment to test your
hypothesis.
a) Set up a table to record your data.
a) Record your experimental design
in your notebook.
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2. Imagine that you had thrown the clay
into the air so that it landed on a
tabletop. In your group, discuss and
record your ideas about the
following:
3. Place a thermometer in each solar
cooker and close the lids. You will
want to be able to read the
thermometer without blocking the
path of solar energy and without
opening the boxes.
a) How does the kinetic energy of
the piece of clay change over time?
When is it highest? When is it
lowest?
a) Record and graph the data.
4. Use the evidence that you have
collected to answer the following
questions:
b) How does the potential energy of
the lump of clay change over
time? When is it highest? When is
it lowest?
a) How did your results compare
with your hypothesis?
b) What heating mechanism causes
the cookers to heat up in the first
place?
c) How was kinetic energy
transformed into potential energy?
When did this happen?
c) What are the different heat
transfer mechanisms that are
taking place in the cookers? Use
diagrams to record your ideas in
your notebook.
d) How was kinetic energy
transformed into heat? When
did this happen?
e) Find a way to represent the
changes in these three forms of
energy over time. Record your
ideas on the sheet of graph paper
that shows the path of the
modeling clay.
d) What mechanism keeps the heat
from escaping?
e) What improvements could be
made to the cooker if you had
to do it over again?
Be careful when you touch items after they
have been in the solar cooker. They will be hot.
Part B: Kinetic Energy, Potential
Energy, and Heat
1. The following is a thought
experiment. The graph shows the
path of a small lump of modeling
clay that is thrown into the air.
a) Copy the graph onto a sheet
of graph paper.
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a) Begin a concept map to show
how the units are interconnected.
Complete the concept map as
you work through this part of the
activity.
Part C: Energy Units and Conversions
1. Look at the conversion table. (In this
activity you will record all your data
in metric units. The table gives both
metric and English equivalents to all
the units that you will be using in
this activity. Refer to this table
whenever necessary.)
Energy Conversion Table
Heat
1 kcal (kilocalorie) = the heat needed to raise the temperature of one kilogram of water
from 14.5°C to 15.5°C
1 Btu (British thermal unit) = the heat needed to raise the temperature of one pound
of water from 60°F to 61°F
1 kcal = 1000 cal = 3.968 Btu
Force, mass, and velocity
1 kg = 0.069 slug
acceleration of gravity (g) = 9.8 m/s2 = 32 ft/s2
1 N (newton) = 1 J/m (joule per meter) = 0.225 pounds
1 m/s = 3.28 fps (feet per second) = 2.24 mph (miles per hour)
Energy and work (the mechanical equivalent of heat)
1
1
1
1
kcal = 1000 cal = 4184 J (joules)
Btu = 252 cal = 777.9 ft-lb (foot-pounds) = 1055 J
kWh = 3,600,000 J = 3413 Btu
quad (Q) = 1015 Btu
Power (the rate at which work is done)
1 W (watt) = 1 J/s (joules per second)
1 hp (horsepower) = 550 ft-lb/s = 746 W
3. Work is defined as the product of a
force times the distance through which
the force acts. The work needed to lift
the steel ball a certain vertical distance
is the force (weight of the ball, in
newtons) times the vertical distance, or
W = F • d,
2. Do you think that you can produce
power equal to that of a 100-W light
bulb? Obtain and weigh a steel ball.
a) Record the weight of the ball in
newtons. As shown by the
conversion tables, a newton is a
unit of force. The weight of the
ball is the same as the force
exerted on the ball by the pull of
gravity. Show your work in your
EarthComm notebook.
where W is work in joules (J),
F is force in newtons (N), and
d is the height it is raised in
meters (m).
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or climbing stairs (how fast?).
Do this as a “thought experiment”,
one that you will describe (with
calculations) but not conduct.
a) In order for an object to obtain
kinetic energy, work must be done
on it. Calculate the work necessary
to lift the steel ball to a height
of 2 m.
a) Record your thought experiment.
Show your calculations.
4. Power is the rate at which work is
done. The power you produce when
you lift the ball is equal to the work
divided by the time it took to lift the
ball. If you lift the ball a number of
times in a certain time period, the
average power you produce is equal to
the work of each lift, times the number
of lifts, divided by the total time it
took to do all of the lifting. Remember
that the work is measured in joules
and the time is measured in seconds.
6. The energy it took to produce the
power to the ball came from
chemical energy. In this case, the
chemical energy was energy stored
in the food you ate for breakfast.
Assume that your body was 100%
efficient (all of the stored energy is
converted into kinetic energy).
a) Calculate the number of times
you could lift the ball to equal a
200 Calorie candy bar (use the
table and remember that one
food calorie = 1 kilocalorie or
1000 calories).
P = W/t
where P is power in watts (W),
W is work in joules (J), and
t is time in seconds (s).
b) In nature, no energy change is
100% efficient. Some energy is
lost to the environment. In the
case of lifting the ball, what form
does the lost energy take?
a) Calculate the power produced by
lifting the ball 10 times in one
minute. Note from the table that
the unit for power is the watt.
One watt = one joule per second.
7. As a class discuss the question of
whether a person can produce as
much power as a 100-W light bulb.
5. In your group, discuss what a person
would have to do to produce as
much power as a 100-W bulb.
Examples include running (how fast?)
a) Record the results of your
discussion.
Reflecting on the Activity and the Challenge
lift a ball can be equivalent to the power
produced by a 100-W light bulb. These
activities will help you think about how
energy is transformed into a form that
you can use. It will also help you think
about ways to conserve energy resources
so that your community can meet its
growing energy needs.
In Part A of this activity you looked at
different ways that heat transfer occurs.
Part B helped you to understand the
concepts of potential and kinetic energy.
In Part C you explored concepts of
work, power, and units of energy. You
also completed calculations to determine
whether or not the exertion required to
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Digging Deeper
HEAT AND ENERGY CONVERSIONS
Geo Words
Heat Transfer
heat: kinetic energy of
atoms or molecules
associated with the
temperature of a body of
material.
kinetic energy: a form
of energy associated with
motion of a body of
matter.
temperature: a measure
of the energy of
vibrations of the atoms or
molecules of a body of
matter.
heat transfer: the
movement of heat from
one region to another.
absolute zero: the
temperature at which all
vibrations of the atoms
and molecules of matter
cease; the lowest possible
temperature.
conduction: a process of
heat transfer by which
the more vigorous
vibrations of relatively hot
matter are transferred to
adjacent relatively cold
matter, thus tending to
even out the difference in
temperature between the
two regions of matter.
thermal insulator: a
material that impedes or
slows heat transfer.
Heat is really the kinetic
energy of moving molecules.
energy flow
Temperature is a measure of hot
cold
this motion.The term heat
transfer refers to the
tendency for heat to move
Radiation
from hotter places to colder
Conduction
places. Many of the important
aspects of heat transfer (see
Figure 1) that you observed
with the solar cooker had to
rising
do with heat conduction,
heated
which is one of the processes
air
of heat transfer. All matter
consists of atoms. At
cold air
temperatures above absolute
zero (about –273°C, the
coldest anything can be!), the
Convection
atoms vibrate.You sense those
Figure 1 Three types of heat transfer.
vibrations as the temperature
of the material.The stronger the vibration, the hotter the material.
When a hotter material is in contact with a colder material, collisions
between adjacent vibrating atoms in the two materials cause the energy
of the vibrations to even out, cooling the hot material and warming the
cold material.
Conduction is the type of heat transfer you experience when you take a
hot bath, when you heat a piece of metal, or when the air cools a cup of hot
coffee left on top of a table. For instance, when you put a metal pot on the
stove, only the bottom of the pot is in contact with the burner, yet the heat
flows through the entire pot all the way to the handle. Materials differ
greatly in how well they conduct heat. In thermal insulators, like
Styrofoam, crumpled paper, or a down jacket, the heat flows slowly.Thermal
insulators like these contain a large amount of trapped air. Air is a poor
conductor because the air molecules are not in constant contact. Metals, on
the other hand, are very good conductors of heat. Heat conduction is very
important in your community. Keeping your home warm in the winter
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Geo Words
convection: motion of a fluid
caused by density differences
from place to place in the
fluid.
convection cell: a pattern of
motion in a fluid in which the
fluid moves in a pattern of a
closed circulation.
electromagnetic radiation:
the movement of energy, at
the speed of light, in the form
of electromagnetic waves.
would be very difficult (and expensive) without the insulating properties of
the walls and the roof. Improving the insulation of your home by using
insulating materials like those shown in Figure 2 can greatly reduce the
amount of energy needed to heat or cool your home.
Another form of heat transfer is
convection, which is important in
liquids and gases.When a liquid or a
gas is heated, its density decreases.
That causes it to rise above its denser
surroundings. In a room heated with a
wood stove or a steam or hot water
radiator, for instance, a natural
circulation pattern is developed.The
hot air from the stove rises towards
the ceiling and cooler air travels down
the walls and across the floor towards
the stove.That kind of circulation is
Figure 2 Thermal insulation helps to keep
called a convection cell. Heat
your home warm. It conserves energy
convection is also very important to
needed for space heating.
your community. Many of the features
of weather, such as sea breezes and thunderstorms, are caused by
convection. Also, the way that you heat or cool your home depends strongly
on heat convection.
Figure 3 The Sun emits electromagnetic radiation that
warms the surface of the Earth.
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A third form of heat transfer is
electromagnetic radiation.
Everything emits
electromagnetic radiation.
Examples of electromagnetic
radiation are radio and
television waves, visible light,
ultraviolet light, and x-rays.
Hotter materials emit more
energy of electromagnetic
radiation than colder materials.
The warmth you feel from a
hot fire, the Sun, or a light bulb
is due to electromagnetic
radiation traveling (at the
speed of light!) from the hot
object to you.
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Radiation is important to the community for many reasons. Solar radiation
causes things in the community to be heated. Solar radiation heated the
solar cooker. It also heats someone standing in the sunshine on a cold
winter day, or a parked car in the Sun in the summer with all its windows
closed. If a building is designed appropriately, the heat from the Sun can
substitute for heat from other energy resources for space heating and hot
water. Using insulation or light-colored reflective materials reduces solar
heating in warmer months when heat is not desired.
Energy, Work, and Power
In the investigation, you dealt with four forms of energy: energy of motion,
called kinetic energy; energy of position, called potential energy; energy
stored in the chemical bonds of a substance, called chemical energy, and
heat. Kinetic energy and potential energy together are called mechanical
energy.You know that objects in motion have energy, because of what they
can do to you when they hit you.The energy of motion is called kinetic
energy.The more mass the body has, and the faster it is moving, the more
kinetic energy it has.When you threw (or imagined throwing) the lump of
modeling clay up in the air, you gave it kinetic energy.The kinetic energy was
gradually converted to potential energy.When the lump reached its highest
point, its kinetic energy was at a minimum. On the way down, the lump
regained its kinetic energy.When it hit the table, all of its kinetic energy was
changed to heat.The change in
temperature was so small that
you would need a very sensitive
thermometer to measure it.
That’s an example of how kinetic
energy is changed to heat energy
by friction.When you rub your
hands together to keep them
warm, you are converting kinetic
energy to heat by friction. Of
course, you are always
resupplying your hands with
kinetic energy by the action of
your arm muscles.
Geo Words
potential energy:
mechanical energy
associated with position
in a gravity field; matter
farther away from the
center of the Earth has
higher potential energy.
chemical energy: energy
stored in a chemical
compound, which can be
released during chemical
reactions, including
combustion.
mechanical energy:
the sum of the kinetic
energy and the potential
energy of a body of
matter.
friction: the force exerted
by a body of matter when
it slides past another body
of matter.
Figure 4 A coal-powered train is an example of
how chemical energy stored in coal is converted
into heat energy that in turn is converted to
mechanical energy.
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Geo Words
work: the product of the
force exerted on a body and
the distance the body moves
in the direction of that force;
work is equivalent to a change
in the mechanical energy of
the body.
force: a push or pull exerted
on a body of matter.
power: that time rate at
which work is done on a body
or at which energy is
produced or consumed.
watt: a unit of power.
horsepower: a unit of power.
biomass: the total mass of
living matter in the form of
one or more kinds of
organisms present in a
particular habitat.
In physics, the term work has a very specific meaning.Work is equal to the
force you exert on some object multiplied by the distance you move the
object in the direction of the force.The importance of work is that it causes
a change in the mechanical energy (kinetic and/or potential) of the object.
When you threw the lump of modeling clay up in the air, your hand did the
work. It exerted an upward force on the clay for a certain distance to give it
its kinetic energy.
Power is the term used for the rate at which work is done or at which
energy is produced or used.Think once more about the now-famous lump
of modeling clay.You could have given it its upward kinetic energy by
swinging your arm upward slowly for a long distance, generating low power
but for a long time. Or, you could have swung your arm upward fast over
only a short distance, generating high power but for only a short time.
Whenever your muscles move your own body or some other object, you
are generating power.The watt is the unit of power that is commonly used
to describe the power of electrical devices. Horsepower is the unit of
power that is often used to describe the power of other mechanical devices.
Converting Heat into Mechanical Energy
You have explored the idea that mechanical
energy always tends to be converted into heat
by friction. Nothing on Earth is completely
frictionless, although some things, like air-hockey
pucks, involve very little friction. Only in the
emptiness of outer space can bodies move
without friction. But how about energy
conversion in the opposite direction: from heat
to mechanical energy?
Figure 5 Coal is fed by a
conveyor into a combustion
chamber, where it is burned.
The conversion of heat into mechanical energy is
central to most of the processes for producing
electricity from energy resources.These
resources include coal, natural gas, petroleum,
sunlight, biomass, and nuclear energy. In these
processes, water is heated to produce steam.
When water boils (at atmospheric pressure) it
undergoes about a thousand-fold increase in
volume.The pressure of the steam exerts a force
that does work to increase the kinetic energy of
a turbine.The steam pressure is used to turn a
turbine that generates electricity.
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The Second Law of Thermodynamics states that you can never
completely convert heat into mechanical energy. In fact, in converting any
form of energy into another, there is always a decrease in the amount of
“useful” energy. Stated in general terms, the efficiency of a machine or
process is the ratio of the desired output (work or energy) to the input:
% Efficiency =
useful energy or work out
× 100
energy or work in
Electrical power plants have efficiencies of about 30%. An efficiency of
33% means that for every three trainloads of coal that are burned to
produce electricity, the chemical heat energy from only one of those
trainloads is converted to electricity.
Some methods for generating electricity are not based on the conversion
of heat to mechanical energy. Hydropower and wind power are examples.
In hydropower, the mechanical energy of the falling water is converted
directly to the mechanical energy of the rotating turbine.The efficiency of
hydropower is only about 80% rather than 100%, however, because of
friction and the incomplete use of available mechanical energy. Similarly, the
wind already has mechanical energy.The efficiency of wind power is no
greater than about 60%, mainly because some of the wind goes around the
turbine without adding to its rotation. Actual efficiencies of most wind
turbines range from 30% to 40% (The windmills shown in Figure 6 have an
efficiency of only 16%.) By comparison, the efficiency of a normal automobile
engine is about 22%.
Geo Words
Second Law of
Thermodynamics: the law
that heat cannot be
completely converted into a
more useful form of energy.
thermodynamics: a branch
of physics that deals with the
relationships and
transformations of energy.
efficiency: the ratio of the
useful energy obtained from
a machine or device to the
energy supplied to it during
the same time period.
Check Your
Understanding
1. What are some of the
methods for
generating energy that
are based on the
conversion of heat to
mechanical energy?
2. Describe the three
processes of heat
transfer.
3. In your own words
define mechanical
energy.
4. Why can’t the
efficiency of a device
be more than 100%?
Figure 6 The efficiency of these windmills is only about 16%. Modern wind
turbines have efficiencies between 30% and 40%.
5. Why is the efficiency of
a device always less
than 100%?
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Understanding and Applying What You Have Learned
1. a) Explain how all of the different
parts of the solar cooker work
in terms of different heat
transfer processes.
b) How would you adapt your
solar cooker to make it more
effective and efficient?
2. Describe how a one-liter and twoliter container of water in the same
oven differ in their heat and their
temperature.
3. Describe how you think heat is
transferred in the following
situations:
a) A cold room becomes warm
after turning on a hot-water
radiator.
b) Your hand is heated as you
grasp the handle of a heated
pan on the stove.
c) The bottom of a pan is heated
when placed on an electric
burner.
d) A cold room becomes warm
after window drapes are opened
on a sunny day.
4. If the energy input of a system is
2500 cal and the energy output is
500 cal, what is the efficiency of
the system?
5. A 300 hp engine is equivalent
to how many foot pounds per
second? In your own words
state what this means.
6. When you drive in a car, energy is
not lost, even though gasoline is
being used up. Use what you have
learned in this activity to explain
what happens to this energy.
Preparing for the Chapter Challenge
Your Chapter Challenge is to help
community members think about how
they will meet their growing energy
needs. Draft an introduction to your
report. Use what you have learned in
this activity to explain how energy
resources are used to do work. Help
people to understand how mechanical
energy is converted to heat in the
devices they use in their everyday
lives. You might also begin to think
about steps that community members
might take to improve their energy
efficiency.
Inquiring Further
What is a perpetual-motion
machine, and why can no one get
a patent for one?
1. Perpetual-motion machines
The United States Patent Office
receives many applications for
perpetual-motion machines. All the
applications are turned down.
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4. Solar cooking applications
2. Improving efficiencies of electricity
generation
In your investigation, you explored
a model of one kind of solar food
cooker. Research:
Innovative methods for power
generation are now being
developed to improve the
efficiency of generating electricity
from energy resources. What are
some new methods for generating
electricity from coal, natural gas,
or oil that have improved
efficiencies? Visit the EarthComm
web site to help you find this
information.
• How people are using solar
cookers and reducing the
consumption of wood and fossil
fuels for cooking food.
• Where are solar cookers most
commonly used?
• Are they a suitable energy
alternative for your community?
3. History of science
• How does the use of a solar
cooker reduce the effect on the
biosphere?
Research the work of James
Prescott Joule. A Scottish physicist,
Joule conducted a famous
experiment to observe the
conversion of mechanical energy to
heat energy. How did the
experiments help Joule to conclude
that heat is a form of energy?
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