energy used bycar accessories

rolling friction

drive systemfrictionengine losses

friction with air

58 Chapter 3 • Designing Effi cient Systems NEL

3.1 Energy on the LooseEnergy 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). Th is

is oft en 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 In mechanical systems, energy is most oft en 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. Th e

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. Th e

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 fi nely tuned, extremely expensive race car can use

only about 34 % of the energy in the gasoline to mobilize the moving

parts of the engine.

lost energy: energy that has escaped from a system

transformed: changed from one form to another

transferred: moved from one place to another

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.

Figure 2 Energy losses in a typical car

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hot drain water,about 35 °C

cooled drainwater,

about 20 °C

to water heater/fixtures

incoming cold water,about 10 °C

preheated water,about 25 °C

Lost Energy in Social SystemsSocial 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 eff ective cleaning service, for

example, would be one that cleans homes to the

customer’s satisfaction. Th e 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?

3.1 Energy on the Loose 59NEL

TRY THIS: Identify Energy Losses

Energy losses occur in all systems, including toys and household appliances. In this activity, you will examine familiar objects to identify such losses.

Equipment and Materials: mechanical toy; lettuce spinner; egg beater; hand drill; handheld hair dryer; toaster

Get your teacher’s permission before using anyelectrical appliance.

Handle all tools and materials safely.

1. With your group, examine each system given to you.

2. Discuss the purpose of each device and how energy is used to make the system work.

3. Look for ways energy losses might occur from these devices or ones like them.

A. For each system, what energy losses did your group identify?

B. Which types of energy losses seem to be most common?

SKILLS MENU: observing, analyzing

Energy WatchdogsEnergy 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. Th is 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 fi rst 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. Figure 4 Drain heat recovery systems use hot waste water to preheat incoming cold water.

Figure 3 Where might energy losses occur when cleaning this messy room?

5.A., 7.C.5.A., 7.C.SKILLS HANDBOOK

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High-efficiency fireplaces keepwarm air circulating withinthe home.

Improved insulation in the walls and ceiling reduces energy loss in the winterand energy entry in the summer.

High-efficiency windows alsoreduce energy loss in winter and energy entry in the summer.

Weather sealing around windowsand doors stops warmed air fromescaping in winter.

A high-efficiency furnace producesmore heat energy from a givenamount of fuel.

60 Chapter 3 • Designing Effi cient Systems NEL

Figure 5 Reducing unwanted energy transfer is one way of increasing the effi ciency of home heating and cooling systems.

1. (a) In your own words, defi ne “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?

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?

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?

CHECK YOUR LEARNING

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.

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