3.1
lost energy: energy that has escaped
from a system
transformed: changed from one form
to another
transferred: moved from one place to
another
Energy on the Loose
Energy is used to do work. However, no system can convert all of its
input energy into useful work. Scientists understand that energy
cannot be destroyed, or vanish into nothing. However, it can “escape”
from a system when not used to perform useful work (Figure 1). This
is often referred to as lost energy.
In systems, energy can be lost when it is transformed from one form
to another (for example, chemical energy to thermal energy). Energy
can also be lost when it is transferred from one part of the system to
another (for example, driver gear to follower gear).
Lost Energy in Mechanical Systems
Figure 1 About one-third of a home’s
energy goes to heating water. Most of
that energy is lost when the hot water
goes down the drain.
In mechanical systems, energy is most often lost as parts of the system
warm up due to friction. Energy may also escape from mechanical
systems through excess vibration and unwanted sound.
Cars are notorious energy wasters. Most cars run on gasoline. The
chemical energy stored in gasoline is transformed into motion in the
engine. Engine motion is then transferred to the drive wheels, making
the car move.
In a typical engine, only about one-quarter of the chemical energy
in the gasoline is converted into mechanical work by the engine. By
the time that energy is transferred into the drive wheels, less than
20 % of the gasoline’s energy is actually used to move the car. The
remaining energy is lost through such things as hot exhaust gases
(fumes), heating the water in the car’s cooling system, overcoming
friction in the car’s moving parts, vibration, and sound (Figure 2).
Even the motor of a finely tuned, extremely expensive race car can use
only about 34 % of the energy in the gasoline to mobilize the moving
parts of the engine.
friction with air
engine losses
energy used by
car accessories
drive system
friction
rolling friction
Figure 2 Energy losses in a typical car
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Lost Energy in Social Systems
Social systems also need to be carefully designed
and managed. A system that uses more materials,
time, or human energy than is needed will be
expensive. It will likely also accomplish less work
than it could. An effective cleaning service, for
example, would be one that cleans homes to the
customer’s satisfaction. The service would not waste
cleaning materials, time, or electrical energy. Now,
think about those times when you are asked to
clean your room (Figure 3). In what ways do you
create “lost energy” when performing this service?
Figure 3 Where might energy losses occur when cleaning this
messy room?
TRY THIS: Identify Energy Losses
SKILLS HANDBOOK
5.A., 7.C.
SKILLS MENU: observing, analyzing
Energy losses occur in all systems, including toys and household
appliances. In this activity, you will examine familiar objects to
identify such losses.
1. With your group, examine each system given to you.
Equipment and Materials: mechanical toy; lettuce spinner;
egg beater; hand drill; handheld hair dryer; toaster
3. Look for ways energy losses might occur from these devices
or ones like them.
Get your teacher’s permission before using any
electrical appliance.
A. For each system, what energy losses did your group identify?
Handle all tools and materials safely.
2. Discuss the purpose of each device and how energy is used
to make the system work.
B. Which types of energy losses seem to be most common?
Energy Watchdogs
Energy losses are not only costly, they consume resources.
Burning more gasoline and natural gas than needed wastes
valuable fossil fuel. Wasteful use of electricity places more
strain on the electrical delivery system. This may contribute
to the need for additional generating stations, which are
expensive to build and maintain. New technologies continue
to be developed to recapture lost energy or to prevent energy
from escaping in the first place. With mechanical systems,
specialized lubricants reduce energy loss from friction.
Canadians use large quantities of energy to keep their
homes cool in the summer and warm in winter. Sometimes
thermal energy escapes from homes through poorly insulated
walls and roofs, or through gaps around windows and doors.
When this occurs, additional resources are used to replace
the lost energy. Energy recovery systems in drains can
capture up to 85 % of the thermal energy lost from hot waste
water (Figure 4). Heat pumps and exchangers in homes help
recapture heat energy from home heating and ventilation
systems.
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hot drain water,
about 35 °C
to water heater/
fixtures
preheated water,
about 25 °C
incoming cold water,
about 10 °C
cooled drain
water,
about 20 °C
Figure 4 Drain heat recovery systems use hot
waste water to preheat incoming cold water.
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Canadians are doing many things to optimize, or make better use of,
energy resources for home heating and cooling (Figure 5). As concern
for the environment increases, these and other technologies will likely
be in great demand.
Improved insulation in the walls and
ceiling reduces energy loss in the winter
and energy entry in the summer.
High-efficiency fireplaces keep
warm air circulating within
the home.
High-efficiency windows also
reduce energy loss in winter and
energy entry in the summer.
A high-efficiency furnace produces
more heat energy from a given
amount of fuel.
Weather sealing around windows
and doors stops warmed air from
escaping in winter.
Figure 5 Reducing unwanted energy transfer is one way of increasing the efficiency of home heating and cooling systems.
CHECK YOUR LEARNING
1. (a) In your own words, define “energy.”
(b) Since energy cannot be destroyed, what do we mean
when we say that energy is lost from a system?
(c) What is the most common way that energy is lost in
mechanical systems?
3. (a) How much of the energy in gasoline is used to actually
make a car move?
(b) Where is energy lost in a car?
4. (a) In what ways are we beginning to recapture lost energy?
(b) What advantages to the environment does this have?
2. (a) What does friction have to do with energy losses?
(b) What do we do to reduce the negative effects of friction
in systems?
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