Cool Physics of Heat

8/14/2019 Cool Physics of Heat

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Created at Curtin University of Tec

The Cool Physics of Heat

HEAT: A transfer of energy due to a

difference in temperature.

Slide show and images by Colin [email protected]

Students are invited to edit this work according to the Creative

Commons license on the References and Copyright slide.
mailto:[email protected]:[email protected]


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Preface

An introductory outline of the Physics of Heat.

I created this presentation at Curtin Sarawak Malaysia as a basis for

Foundation Physics students and others to edit and expand.

Do you have a story involving heat that you would like to contribute to this

presentation? Students are invited to edit this work according to the Creative

Commons license on the References and Copyright slide. You may addphotos from your camera phone that illustrate a physical phenomena, or add

a description of any physical process that involves heat or temperature.

Changes should conform to academic practice; please do not insert images

that are protected by copyright, or paraphrase sentences from Physics text

books. Add a slide at the end with your name, email, the date and citing any

references.

Except where otherwise noted, this work is licensed under the Creative

Commons Attribution-Share Alike 2.5 Malaysia License.

By: Colin McAllister, teaching Physics in the School of Foundation &

Continuing Studies, at Curtin University of Technology, Sarawak, Malaysia.


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The combustion of gas in air is a source of heat.


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Did someone throw cold water on your idea? Did you get your fingers burned in a business deal? These two idioms show that heat is a macroscopic

phenomena that we are all familiar with.

Heat exchange occurs in all man-made and naturalsystems. The Perpetual Motion Machine does not exist! Every activity causes energy to be converted to heat. Physics explains the macroscopic properties of heat in

terms of the microscopic motion of molecules. Every science and every branch of engineering uses

measurements of energy and temperature to quantifythermal properties.


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Heat as Energy Transfer

HEAT is the energy transferred from one

object to another because of the

difference in temperature.

Heat flows from hot to cold.

Units of heat: calorie, kilocalorie, Calorie

and Joule.

Physicists use the SI unit: Joule or J

Temperature is measured in oC, oF oroK


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Conservation of Energy

Heat is equivalent to work done.

Work Done is Force x Distance (parallel)

Friction converts mechanical energy toheat. How can we reduce unwanted friction?

The brakes on a vehicle convert thekinetic energy of the vehicle to heat

energy in the brake pads, disk or drum. Excessive braking wastes petrol. Explain

this in terms of the physics involved.


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Internal Energy

The internal energy of a material is due to themotion of molecules.

The temperature of a material is a measure of its

internal energy. Molecules in a solid or liquid are restricted, so

their motion is in the form of vibration.

Molecules in a gas or are free to move around,

and have Kinetic Energy. When internal energy flows from one place to

another place, it is known as heat.


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Specific Heat

The specific heat capacity of water determines the energy needed to heat it.


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Specific Heat

Specific heat capacity, also known simply as

specific heat, is the measure of the heat energy

required to increase the temperature of a unit

quantity of a substance by a certain temperatureinterval. (wikipedia.org)

In a solid, the rise in temperature is due to the

molecules vibrating at larger amplitude. In a gas,

the rise in temperature is due to the moleculesmoving at faster speeds.


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Latent Heat

Boiling water undergoes a phase change from liquid to gas.

The Strokkur geyser

in Iceland ejects a

jet of water 60 to

100 feet into the air.

Geothermal heat

changes some

underground

water from

liquid to gas,increasing the

volume and

pressure,

powering the

eruption


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Latent Heat

Latent Heat is the amount of energy in the formof heat released or absorbed by a substanceduring a change of phase state (i.e. solid, liquid,

or gas), also called a phase transition(wikipedia.org)

Phase Transitions that release heat:condensation, freezing and deposition (frost).

Phase Transitions that absorb heat: melting,evaporation, boiling, sublimation.

(Some materials, e.g. CO2 undergo sublimation:

changing directly from a solid to a gas.)


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Heat Transfer Mechanisms

Convection: heat carried by the flow of a

fluid, such as air or water.

Thermal Conduction: flow of thermal

energy through a material.

Thermal Radiation: electromagnetic

radiation due to temperature.

Thermal Radiation is key to explaining

how global warming occurs.


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Convection

A fan drives transfer of heat by forced convection of

air.


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Convection

Convection involves the movement of a fluid betweentwo regions of different temperature. The fluid may be agas (e.g. air) or a liquid (e.g. water).

In free convection the movement of the fluid is due tothe difference in temperature between the regions. Thefluid expands in the warmer region, causing its density tobe lower. It contracts to its original density in the coolerregion. Lower density fluid will rise and higher densityfluid will fall under gravity, causing the fluid to flow as acurrent. E.g. ocean currents.

In forced convention, the fluid is already moving due to apressure difference, perhaps driven by a pump or a fan.

The effectiveness of thermal conduction depends on theviscosity and on the specific heat of the fluid.


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Thermal Conduction

Conduction is the transfer of heat within a material, bythe random transfer of kinetic energy from moleculeswith a high amplitude of vibration to neighbouringmolecules with a lower amplitude of vibration.

Metals contain many free electrons, known asconduction-band electrons. These contribute to theconduction of heat in metals.

The thermal conductivity of a material is a measure ofhow well it conducts heat.

Copper and Aluminium have a high thermal conductivity.

Air has a low thermal conductivity. Insulating materials,like polystyrene foam, have a high air content.


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Thermal Radiation

Every object emits thermal radiation from its surface due to itstemperature.

Thermal radiation is electromagnetic radiation that is transmitted bythe electrons in the atoms of the radiating object.

Everyday objects emit thermal radiation that is in the infrared regionof the electromagnetic spectrum.

A hot object, like the filament of a light bulb, emits infrared andvisible thermal radiation.

Thermal radiation is transmitted through air or through the vacuumof space.

Thermal radiation transports heat from a hotter surface to a cooler

surface, e.g. light from the surface of the Sun to the Earth. The thermal radiation inside an enclosed oven is at equilibrium,because all the walls are at the same temperature.


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Global Warming

Huge tabular icebergs, calved from the ice shelf in the Southern Ocean's WeddellSea. (Photo courtesy of Mike Vecchione, NOAA National Marine Fisheries Service),


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Global Warming

Thermal Radiation is key to explaining how GlobalWarming occurs The Greenhouse Effect.

The average temperature of the Earth was constantwhen the thermal radiation emitted into space, balancedthe solar energy absorbed

Burning of fuel and destruction of forest increases thequantity of greenhouse gases in the Earths atmosphere

Greenhouse gases like carbon dioxide and methane areso called because they behave like the glass that keepsa greenhouse warm.

Greenhouse gases absorb thermal radiation from theEarths surface, causing the Earth to become warmer.

A small increase in temperature causes many bigchanges including melting polar ice and rising sea level.


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Heating and Cooling

The exhaust pipe of an internal combustion engine.


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Heating and Cooling

Every gadget, from the thinnest mobile phone to the largest

electricity generating station, produces heat as a by-product.

Architects use the physics of heat to design buildings that are

comfortable and that make efficient use of energy.

Computer Engineers add cooling fins and fans to computers; toremove the heat caused by currents inside the silicon chips.

Materials scientists investigate existing materials and design new

materials with special thermal properties.

When any space vehicle re-enters the Earths atmosphere, heat is

generated by the friction between the air and the vehicle. Tiles on the surface of the Space Shuttle are designed to insulate

the spacecraft from the high temperature of re-entry.


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Further Study of Heat

Suggestions for further study include: The Kinetic Theory of Gases The Laws of Thermodynamics Statistical Thermodynamics

Differential Equations of Heat Conduction Phonons and Lattice Vibrations Temperature Regulation of the Human Body How to Overclock a Motherboard

Aerogel, also known as Frozen Smoke HVAC Employment Opportunities Cryogenics, the physics and engineering of

temperatures below -150 oC.


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References and Copyright

Slide show and images (cc) 2008 by Colin McAllister,[email protected], teaching at Curtin Universityof Technology, Sarawak, Malaysia.

Except where otherwise noted, this work is licensed

under the Creative Commons Attribution-Share Alike 2.5Malaysia License. To view a copy of this license, visithttp://creativecommons.org/licenses/by-sa/2.5/my/deed.en_GB

Students are invited to edit or contribute to this slide show, inaccordance with the above license.

Ref: D.C. Giancoli, Physics Principles with Applications, publishedby Prentice Hall.

Ref: www.wikipedia.org for some definitions.

Iceberg photo: http://publicdomainclip-art.blogspot.com/
mailto:[email protected]://creativecommons.org/licenses/by-sa/2.5/my/deed.en_GBhttp://www.wikipedia.org/http://publicdomainclip-art.blogspot.com/http://publicdomainclip-art.blogspot.com/http://publicdomainclip-art.blogspot.com/http://www.wikipedia.org/http://creativecommons.org/licenses/by-sa/2.5/my/deed.en_GBmailto:[email protected]

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Cool Physics of Heat