work energy and heat (1)

Copyright 2008 Pearson Education, Inc., publishing as Pearson Addison-Wesley

Hewitt/Suchocki/Hewitt

Conceptual Physical Science Fourth Edition

(Adapted for PSC1515)

ENERGY AND

HEAT


This lecture will help you

understand:

Energy and Work Work-Energy Theorem Conservation of Energy Power Efficiency Sources of Energy

Temperature

Heat

Quantity of Heat

The Laws of Thermodynamics

Entropy

Specific Heat Capacity

Conduction, Convection and Radiation


Work

Work

defined as the product of force exerted on an

object and the distance the object moves (in

the same direction as the force)

is done only when the force succeeds in

moving the body it acts upon

equation: work = force distance


Work

Two things enter where work is done:

application of force

movement of something by that force

Work done on the barbell is the average force multiplied by the distance through which the barbell is lifted.


If you push against a stationary brick wall for several

minutes, you do no work

A. on the wall.

B. at all.

C. Both of the above.

D. None of the above.

Work

CHECK YOUR NEIGHBOR


If you push against a stationary brick wall for several

minutes, you do no work

A. on the wall.

B. at all.



Explanation:

You may do work on your

muscles, but not on the wall.

Work

CHECK YOUR ANSWER


Work

The quantity of work done is equal to the amount of force the distance moved in the direction in which the force acts.

Work falls into two categories:

work done against another force

work done to change the speed of an object


Work is done in lifting a barbell. How much work is done in

lifting a twice-as-heavy barbell the same distance?

A. Twice as much.

B. Half as much.

C. The same.

D. Depends on the speed of the lift.

Work

CHECK YOUR NEIGHBOR


Work is done in lifting a barbell. How much work is done in

lifting a twice-as-heavy barbell the same distance?

A. Twice as much.

B. Half as much.

C. The same.

D. Depends on the speed of the lift.

Explanation:

This is in accord with work = force distance. Twice the force for

the same distance means twice the work done on the barbell.

Work

CHECK YOUR ANSWER


You do work when pushing a cart. If you push the cart

twice as far with the same constant force, then the work

you do is

A. less than twice as much.

B. twice as much.

C. more than twice as much.

D. zero.

Work

CHECK YOUR NEIGHBOR


You do work when pushing a cart. If you push the cart

twice as far with the same constant force, then the work

you do is

A. less than twice as much.

B. twice as much.

C. more than twice as much.

D. zero.

Work

CHECK YOUR ANSWER


Energy

Energy defined as that which produces changes in matter

Effects of energy observed only when it is being transferred from one place to another

or it is being transformed from one form to another

Both work and energy are measured in joules.


Power

Power

measure of how fast work is done

equation:

units in joule per second or watt

(One watt = 1 joule of work per second)

Power work donetime interval


A job can be done slowly or quickly. Both may require the

same amount of work, but different amounts of

A. energy.

B. momentum.

C. power.

D. impulse.

Power

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A job can be done slowly or quickly. Both may require the

same amount of work, but different amounts of

A. energy.

B. momentum.

C. power.

D. impulse.

Comment:

Power is the rate at which work is done.

Power

CHECK YOUR ANSWER


Potential Energy

Example: potential energy of 10-N ball is the same in all 3 cases because work done in elevating it

is the same


Potential Energy

Potential Energy

is defined as stored energy due to position, shape, or state. In its stored state, energy has the potential for doing work.

Examples:

Drawn bow

Stretched rubber band

Raised ram of a pile driver


Gravitational Potential Energy

The amount of gravitational potential energy possessed by an elevated object is equal to the work done against gravity in raising it.

Work done equals force required to move it upward the vertical distance moved (W = Fd). The upward force when moved at constant velocity is the weight, mg, of the object. So the work done in lifting it through height h is the product mgh.


Gravitational Potential Energy Equation for gravitational potential energy:

PE = weight height

or

PE = mgh

Gravitational potential energy examples:

Water in an elevated reservoir

The elevated ram of a pile driver


Does a car hoisted for repairs in a service station have

increased potential energy relative to the floor?

A. Yes.

B. No.

C. Sometimes.

D. Not enough information.

Potential Energy

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Does a car hoisted for repairs in a service station have

increased potential energy relative to the floor?

A. Yes.

B. No.

C. Sometimes.

D. Not enough information.

Comment:

And if the car were twice as heavy, its increase in potential energy

would be twice as much.

Potential Energy

CHECK YOUR ANSWER


Work-Energy Theorem Applies to decreasing speed

reducing the speed of an object or bringing it to a halt

Example:

Applying the brakes to slow a moving car. Work is done on it (the friction force supplied by the brakes distance).


Kinetic Energy

Kinetic Energy

is defined as the energy of a moving body

Equation for kinetic energy:

Kinetic energy = 1/2 mass speed2

or

KE = 1/2 mv2

small changes in speed large changes in KE


Must a car with momentum have kinetic energy?

A. Yes, due to motion alone.

B. Yes, when motion is nonaccelerated.

C. Yes, because speed is a scalar and velocity is a vector quantity.

D. No.

Kinetic Energy

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Must a car with momentum have kinetic energy?

A. Yes, due to motion alone.

B. Yes, when motion is nonaccelerated.

C. Yes, because speed is a scalar and velocity is a vector quantity.

D. No.

Explanation:

Acceleration, speed being a scalar, and velocity being a vector

quantity, are irrelevant. Any moving object has both momentum

and kinetic energy.

Kinetic Energy

CHECK YOUR ANSWER


Work-Energy Theorem When work is done on an object to change its KE,

the amount of work done is equal to the change in KE.

Equation for work-energy theorem:

Net work = change in KE

If there is no change in objects energy, then no work is done on the object.

Applies to potential energy:

For a barbell held stationary, no further work is done no further change in energy.

Applies to decreasing energy:

The more kinetic energy something has the more work is required to slow it or stop it


Consider a problem that asks for the distance a fast-

moving crate slides across a factory floor in coming to a

stop. The most useful equation for solving this problem is

A. F = ma.

B. Ft = mv.

C. KE = 1/2mv2.

D. Fd = 1/2mv2.

The Work-Energy Theorem

CHECK YOUR NEIGHBOR


Consider a problem that asks for the distance a fast-

moving crate slides across a factory floor in coming to a

stop. The most useful equation for solving this problem is

A. F = ma.

B. Ft = mv

C. KE = 1/2mv2.

D. Fd = 1/2mv2.

Comment:

The work-energy theorem is the physicists favorite starting point for solving many motion-related problems.


CHECK YOUR ANSWER


Conservation of Energy

Example: energy transforms without net loss or net

gain in the operation of a pile driver


The work done in braking a moving car to a stop is the

force of tire friction stopping distance. If the initial speed

of the car is doubled, the stopping distance is

A. actually less.

B. about the same.

C. twice.



CHECK YOUR NEIGHBOR


The work done in braking a moving car to a stop is the

force of tire friction stopping distance. If the initial speed

of the car is doubled, the stopping distance is

A. actually less.

B. about the same.

C. twice.


Explanation:

Twice the speed means four times the kinetic energy and four

times the stopping distance.


CHECK YOUR ANSWER



Conservation defined in everyday language as to save

physics as to remain unchanged

Law of conservation of energy In the absence of external work input or output, the

energy of a system remains unchanged.

Energy cannot be created or destroyed.



A situation to ponder

Consider the system of a bow and arrow. In drawing the bow, we do work on the system and give it potential energy.

When the bowstring is released, most of the potential energy is transferred to the arrow as kinetic energy and some as heat to the bow.


Suppose the potential energy of a drawn bow is 50 joules,

and the kinetic energy of the shot arrow is 40 joules. Then

A. energy is not conserved.

B. 10 joules go to warming the bow.

C. 10 joules go to warming the target.

D. 10 joules is mysteriously missing.

A situation to ponder CHECK YOUR NEIGHBOR


Suppose the potential energy of a drawn bow is 50 joules,

and the kinetic energy of the shot arrow is 40 joules. Then

A. energy is not conserved.

B. 10 joules go to warming the bow.

C. 10 joules go to warming the target.

D. 10 joules is mysteriously missing.

Explanation:

The total energy of the drawn bow, which

includes the poised arrow, is 50 joules. The

arrow gets 40 joules and the remaining 10 joules

warms the bowstill in the initial system.

A situation to ponder CHECK YOUR ANSWER


Efficiency

Efficiency

how effective a device transforms or transfers useful energy

equation:

a machine with low efficiency greater amount

of energy wasted as heat

Some energy is always dissipated as heat, which

means that no machine is ever 100% efficient.

Efficiency work doneenergy used

100%


A certain machine is 30% efficient. This means the

machine will convert

A. 30% of the energy input to useful work70% of the energy input will be wasted.

B. 70% of the energy input to useful work30% of the energy input will be wasted.

C. As strange as it may seem, both of the above.


Efficiency

CHECK YOUR NEIGHBOR


A certain machine is 30% efficient. This means the

machine will convert

A. 30% of the energy input to useful work70% of the energy input will be wasted.

B. 70% of the energy input to useful work30% of the energy input will be wasted.

C. As strange as it may seem, both of the above.


Efficiency

CHECK YOUR ANSWER


Sources of Energy

Energy sources

Sun

Examples: Sunlight evaporates water; water falls as rain;

rain flows into rivers and into generator turbines; then back to the sea to repeat the cycle.

Solar energy can transform into electricity by photovoltaic cells.

Solar energy indirectly produces wind that can power turbines and generate electricity.


Sources of Energy

Dry-rock geothermal power is a producer

of electricity Water put into cavities in deep, dry, hot rock turns to steam and

powers a turbine at the surface. After exiting the turbine, it

returns to the cavity for reuse.


Solar Power

The power available in sunlight is about 1kW per square meter.

Examples:

Photovoltaic Panels

Hydroelectric Turbines

Wind Turbines

Bio-based Fuels


Energy Storage and Transfer

Electricity

Synthetic Fuels can be created from bio-based products

Hydrogen not a source, but can be generated from

multiple sources and is a good fuel for fuel-cells or internal combustion engines)


Copyright 2008

Pearson Education, Inc.,

publishing as Pearson


understand: Temperature

Heat

Quantity of Heat


Entropy



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Temperature

Temperature

A number that corresponds to the warmth or coldness of an object

Measured by a thermometer

A per-particle property

No upper limit

Definite limit on lower end


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Temperature

Temperature is proportional to the

average translational kinetic energy

per particle in a substance.

Gashow fast the gas particles are bouncing to and fro

Liquidhow fast particles slide and jiggle past one another

Solidhow fast particles move as they vibrate and jiggle in place


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Temperature

Thermometer

Measures temperature by expansion or contraction of a liquid (mercury or colored alcohol)

Reading occurs when the thermometer and the object reach thermal equilibrium (having the same average

kinetic energy per particle)

Infrared thermometers operate by sensing IR radiation


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Temperature

Temperature Scale Celsius scale named after Anders Celsius

(17011744)

zero C for freezing point of water to 100C

for boiling point of water

Fahrenheit scale named after G. D. Fahrenheit (16861736)

32F for freezing point of water to 212F

for boiling point of water

Kelvin scale named after Lord Kelvin (18241907)

273 K for freezing point of water to 373 K for boiling point of water

Absolute zero at - 273C

Same size degrees as Celsius scale

Kelvins, rather than degrees are used


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Theory of Temperature

Kinetic Theory of Matter:

Matter is made up of tiny particles (atoms or molecules) that are always in motion.

Thermal Energy:

The total energy (kinetic and potential) of the submicroscopic particles that make up matter.


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Thermal Energy

Thermal energy in a sparkler

Temperature of sparks very high (2000oC)

Lot of energy per molecule of spark

Total energy is small due to relatively few

molecules per spark

Low transfer of energy


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What Is Heat?

Heat

defined as a flow of thermal energy due to a

temperature difference.

natural direction of heat flow is from a

higher-temperature substance to a

lower-temperature substance.


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Heat 1 liter of water in left pot. 3 liters in right pot.

both pots absorb the same quantity of heat

temperature increases three times as much in the pot with the smaller amount of water.


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When the same amount of heat is added to each of the two

containers of water, the temperature increase in each will

A. be the same.

B. depend on the amount of water in each.

C. be greater for the container with the most water.

D. be less for the container with the smaller amount of water.

Heat

CHECK YOUR NEIGHBOR


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When the same amount of heat is added to each of the two

containers of water, the temperature increase in each will

A. be the same.

B. depend on the amount of water in each.

C. be greater for the contained with the most water.

D. be less for the container with the smaller amount of water.

Comment:

Later, well learn that when heat is added to boiling water, temperature wont increase at all!

Heat

CHECK YOUR ANSWER


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Quantity of Heat

Heat is energy in transit, measured in units of energy joules or calories.

calorie defined as the amount of heat needed to raise the

temperature of 1 gram of water by 1 Celsius degree.

4.18 joules = 1 calorie

so 4.18 joules of heat will change that temperature of

1 gram of water by 1 Celsius degree.


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Quantity of Heat

Energy rating of food or fuel

measured by energy released when they are

metabolized

Kilocalorie

heat unit in labeling food

One kilocalorie or Calorie (with a capital C) is

the heat needed to change the temperature of

1 kilogram of water by 1 degree Celsius.


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Quantity of Heat (summarized)

Heat is energy in transit.

Heat is measured in joules, calories, or Calories.

1 food Calorie equals 1000 calories.To the weight watcher,

the peanut contains 10 Calories.

To the scientist, the peanut releases 10,000 calories.

(41,800 joules) of energy when

burned or digested.


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The quantity of heat needed to raise the temperature of a

certain substance a specific amount is 1 Calorie. This is the

same amount of energy as

A. 1000 calories.

B. 4.18 joules.

C. Both of these.

D. Neither of these.

Quantity of Heat

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The quantity of heat needed to raise the temperature of a

certain substance a specific amount is 1 Calorie. This is the

same amount of energy as

A. 1000 calories.

B. 4.18 joules.

C. Both of these.

D. Neither of these.

Quantity of Heat

CHECK YOUR ANSWER


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You heat a half-cup of tea and its temperature rises by 8C.

How much will the temperature rise if you add the same

amount of heat to a full cup of tea?

A. 0C.

B. 2C.

C. 4C.

D. 8C.

Quantity of Heat

CHECK YOUR NEIGHBOR


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You heat a half-cup of tea and its temperature rises by 8C.

How much will the temperature rise if you add the same

amount of heat to a full cup of tea?

A. 0C.

B. 2C.

C. 4C.

D. 8C.

Quantity of Heat

CHECK YOUR ANSWER


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Thermodynamics

movement of heat

First law of thermodynamics

When heat flows to or from a system, the system gains or loses an amount of heat equal to the

amount of heat transferred.

more specifically,

heat added = increase internal energy + external work

done by the system

Energy can neither be created nor destroyed.


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The Laws of Thermodynamics Second law of thermodynamics

Restates direction of heat flow:

Heat never spontaneously flows from a cold

substance to a hot substance

Examples:

in summer, heat flows from the hot air outside into the cooler interior of a dwelling

in winter, heat flows from the warm inside to the cold exterior

Heat can flow from cold to hot only when work is done on the system or by adding energy from another source

(as in heat pumps and air conditioners, where the

direction of heat flow isnt spontaneous)


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Third Law of Thermodynamics:

No system can reach absolute zero.


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When work is done on a system, compressing air in a tire

pump for example, the temperature of the system

A. increases.

B. decreases.

C. remains unchanged.

D. is no longer evident.


CHECK YOUR NEIGHBOR


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When work is done on a system, compressing air in a tire

pump for example, the temperature of the system

A. increases.

B. decreases.

C. remains unchanged.

D. is no longer evident.

Explanation:

In accord with the first law of thermodynamics, work input

increases the energy of the system.


CHECK YOUR ANSWER


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When a hot cup is filled with cold water, the direction of

heat flow is

A. from the cup to the water.

B. from the water to the cup.

C. random, in no particular direction.

D. nonexistent.


CHECK YOUR NEIGHBOR


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When a hot cup is filled with cold water, the direction of

heat flow is

A. from the cup to the water.

B. from the water to the cup.

C. random, in no particular direction.

D. nonexistent.

Explanation:

The second law of thermodynamics tells us that the direction of

unassisted heat flow is from hot to cold. (If assisted with energy

input, as with an air conditioner for example, then heat can flow

from cold to hot.)


CHECK YOUR ANSWER


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Entropy

Entropy

is a measure of the disorder of a system.

Whenever energy freely transforms from one form to another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy.

The greater the disorder the higher the entropy.


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Entropy

Second law of thermodynamics restatement:

Natural systems tend to disperse from

concentrated and organized-energy states

toward diffuse and disorganized states.

Energy tends to degrade and disperse with time.

The total amount of entropy in any system tends to

increase with time.


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Your garage gets messier each week. In this case, the

entropy of your garage is

A. increasing.

B. decreasing.

C. hanging steady.

D. nonexistent.

Entropy

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Your garage gets messier each week. In this case, the

entropy of your garage is

A. increasing.

B. decreasing.

C. hanging steady.

D. nonexistent.

Comment:

If your garage became more organized each week, then entropy

would decrease in proportion to the effort expended.

Entropy

CHECK YOUR ANSWER


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Specific heat capacity

is defined as the quantity of heat required to change the temperature of 1 unit mass of a

substance by 1 degree.

thermal inertia that indicates the resistance of

a substance to a change in temperature.

sometimes simply called specific heat.


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Substances have their own specific heat capacities.

Example: Filling in a hot apple pie has a greater specific heat capacity than the crust.

Watery filling has more capacity for storing

heat than pie crust.


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The high specific heat capacity of water

Has higher capacity for storing energy than almost any other substance

Involves various ways that energy can be absorbed

increase the jiggling motion of molecules, which raises the temperature

increase the amount of internal vibration or rotation within the molecules, which becomes potential energy

and doesnt raise temperature

then water molecules can absorb energy without increasing translational kinetic energy


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Specific heat affects climate

for Europeans, in addition to warm jet streams in the atmosphere, current in the Atlantic Ocean carries warm water

northeast from the Caribbean regions and retains much of its

internal energy long enough to reach the North Atlantic Ocean.

Energy released is carried by westerly winds over the European

continent.


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Which has the higher specific heat, water or land?

A. Water.

B. Land.

C. Both of the above are the same.


Specific Heat

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Which has the higher specific heat, water or land?

A. Water.

B. Land.

C. Both of the above are the same.


Explanation:

A substance with small temperature changes for large heat

changes has a high specific heat capacity. Water takes much

longer to heat up in the sunshine than does land. This difference

is a major influence on climate.

Specific Heat

CHECK YOUR ANSWER


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understand:

Conduction Convection Radiation Global Warming and the Greenhouse Effect Energy and Change of Phase


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Heat Transfer

Processes of thermal energy transfer:

Conduction

Convection

Radiation


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Conduction

Conduction

Transfer of internal energy by electron and molecular collisions within a substance


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Heat Transfer: Conduction

Conduction occurs

predominately in solids

where the molecules remain

in relatively restricted

locations.

When you stick a nail into

ice, does cold flow from the

ice to your hand, or heat

from your hand to the ice?


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If you hold one end of a metal bar against a piece of ice,

the end in your hand will soon become cold. Does cold flow

from the ice to your hand?

A. Yes.

B. In some cases, yes.

C. No.

D. In some cases, no.


CHECK YOUR NEIGHBOR


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If you hold one end of a metal bar against a piece of ice,

the end in your hand will soon become cold. Does cold flow

from the ice to your hand?

A. Yes.

B. In some cases, yes.

C. No.

D. In some cases, no.

Explanation:

Cold does not flow from the ice to your hand. Heat flows from your

hand to the ice. The metal is cold to your touch, because you are

transferring heat to the metal.


CHECK YOUR ANSWER


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Conduction

Insulation

Doesnt prevent the flow of internal energy

Slows the rate at which internal energy flows

Example: Rock wool or fiberglass between walls slows the transfer of internal energy from a warm

house to a cool exterior in winter, and the

reverse in summer


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Conduction Application

Snow patterns on the roof of a house show

areas of conduction

and insulation.

Bare parts show where heat from

inside has conducted

through the roof and

melted the snow.


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When thermal insulation, such as spun glass or rock wool,

is placed beneath the roof of a house, then in cold weather

the insulation will

A. create heat to warm the house.

B. keep the cold from coming through the roof.

C. slow the flow of heat from inside the house to the outside.

D. stop the flow of heat from inside the house to the outside.

Energy Transfer

CHECK YOUR NEIGHBOR


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Energy Transfer

CHECK YOUR ANSWER

When thermal insulation, such as spun glass or rock wool,

is placed beneath the roof of a house, then in cold weather

the insulation will

A. create heat to warm the house.

B. keep the cold from coming through the roof.

C. slow the flow of heat from inside the house to the outside.

D. stop the flow of heat from inside the house to the outside.

Explanation:

No insulation can stop heat flow. Insulation only slows it. (A fortune awaits the inventor who can come up with the perfect insulator!)


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Good conductors: Composed of atoms with loose outer electrons

Known as poor insulators

Examplesall metals to varying degrees

Poor conductors: Delay the transfer of heat

Known as good insulators

Exampleswood, wool, straw, paper, Styrofoam, cork, liquid, gases, air, or materials with trapped air


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Conduction

Dramatic example: Author John Suchocki walks barefoot without burning his feet

on red-hot coals,due to poor

conduction between the coals

and his feet


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Convection

Convection

Transfer of heat involving only bulk motion of fluids

Examples:

Visible shimmer of air above a

hot stove or above asphalt on a

hot day

Visible shimmers in water due

to temperature difference


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Convection

Cooling by expansion

Opposite to the warming that occurs when air is compressed

Example: The cloudy region above hot steam issuing from the

nozzle of a pressure cooker is

cool to the touch (a

combination of air

expansion and mixing with

cooler surrounding air).

Careful, the part at the nozzle

that you cant see is steamouch!


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Convection Currents

Convection currents produced by unequal heating of land and water.

During the day, warm air above the land rises, and cooler air over the water moves in to

replace it.

At night, the direction of air flow is reversed.


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Convection

Reason warm air rises

Warm air expands, becomes less dense, and is buoyed upward

Air rises until its density equals that of the surrounding air

Example: Smoke from a campfire rises and blends with the surrounding cool air.


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Although warm air rises, why are mountaintops cold and

snow covered, while the valleys below are relatively warm

and green?

A. Warm air cools when rising.

B. There is a thick insulating blanket of air above valleys.



Heat Transfer: Convection

CHECK YOUR NEIGHBOR


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Although warm air rises, why are mountaintops cold and

snow covered, while the valleys below are relatively warm

and green?

A. Warm air cools when rising.

B. There is a thick insulating blanket of air above valleys.



Explanation:

Earths atmosphere acts as a blanket, which for one important thing, keeps Earth from freezing at nighttime.

Heat Transfer: Convection

CHECK YOUR ANSWER


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Radiation

Radiation

Transfer of energy via electromagnetic waves that can travel through empty space


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Heat Transfer: Radiation

Wavelength of radiation is related to the

frequency of vibration.

Low-frequency vibrations long waves

High-frequency vibrations short waves


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Radiation

Emission of radiant energy

Every object above absolute zero radiates

From the Suns surface comes light, or solar radiation

From the Earths surface is terrestrial radiation in the form of

infrared waves below our

threshold of sight


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Wave Frequency - Temperature

(a) A low-temperature (cool)

source emits primarily

low-frequency, long

wavelength waves.

(b) A medium-temperature


medium-frequency.

(c) A high-temperature


high-frequency, short

wavelength waves.


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Radiation

Emission of radiant energy

Peak frequency of radiation is proportional to the absolute temperature of the source ( )

f ~ T


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Emission and Absorption

The surface of any material both absorbs

and emits radiant energy.

When a surface absorbs more energy than it

emits, it is a net absorber, and

temperature tends to rise.

When a surface emits more energy than it

absorbs, it is a net emitter, and

temperature tends to fall.


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Absorption of Radiant Energy:

The ability of a material to absorb and radiate thermal energy is indicated by its color.

Good absorbers and good

emitters are dark in color.

Poor absorbers and poor

emitters are reflective or

light in color.


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Whether a surface is a net absorber or net

emitter depends on whether its

temperature is above or below that of its

surroundings.

A surface hotter than its surroundings will be

a net emitter and tends to cool.

A surface colder than its surroundings will

be a net absorber and tends to warm.


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If a good absorber of radiant energy were a poor emitter, its

temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.



CHECK YOUR NEIGHBOR


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If a good absorber of radiant energy were a poor emitter, its

temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.


Explanation:

If a good absorber were not also a good emitter, there would be a

net absorption of radiant energy, and the temperature of a good

absorber would remain higher than the temperature of the

surroundings. Nature is not so!


CHECK YOUR ANSWER


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Radiation

Reflection of radiant energy

Darkness is often due to reflection of light back and forth many times partially absorbing with each reflection

Good reflectors are poor absorbers


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Which is the better statement?

A. A black object absorbs energy well.

B. An object that absorbs energy well is black.

C. Both say the same thing, so both are equivalent.

D. Both are untrue.

Absorption of Radiant Energy

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Which is the better statement?

A. A black object absorbs energy well.

B. An object that absorbs energy well is black.

C. Both say the same thing, so both are equivalent.

D. Both are untrue.

Explanation:

This is a cause-and-effect question. The color black doesnt draw in and absorb energy. Its the other way aroundany object that does draw in and absorb energy, will, by consequence, be black

in color.

Absorption of Radiant Energy

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Which of the following does NOT emit radiation?

A. A lit fluorescent lamp.

B. A lit incandescent lamp.

C. A burned out incandescent lamp.


Emission of Radiant Energy

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Which of the following does NOT emit radiation?

A. A lit fluorescent lamp.

B. A lit incandescent lamp.

C. A burned out incandescent lamp.


Explanation:

Everything continually emits radiationand everything continually absorbs radiation. When emission is greater than absorption, temperature of the emitter drops. When absorption is greater than emission, temperature increases. Everything is emitting and absorbing radiation continually. Thats righteverything!

Emission of Radiant Energy

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