Thermal Energy

Temperature and HeatChapter 6 Section 1

Contents

Section 1 slide 3 - 30 Section 2 slide 31 - 58 Section 3 slide 59 - 82

Temperature

All matter is made of atoms & molecules

Temperature

All matter is made of atoms & molecules

All these particles constantly move in a random fashion

Temperature

All matter is made of atoms & molecules

All these particles constantly move in a random fashion In all directions at different speeds

Temperature

All matter is made of atoms & molecules

All these particles constantly move in a random fashion In all directions at different speeds Thus they have ________ energy

Kinetic Energy

Faster they move, the more KE they have -> hotter they are

Kinetic Energy

Faster they move, the more KE they have -> hotter they are

As they cool, they slow down

Kinetic Energy

Faster they move, the more KE they have -> hotter they are

As they cool, they slow down

Temperature is a measure of the average value of the kinetic energy of the particles in an object.

Temperature

SI Units are kelvins (K)

Temperature

SI Units are kelvins (K) Celsius scale is more commonly

used. 1 K = 1 degree Celsius

Thermal Energy

Thermal energy is the sum of the KE + PE of all the molecules in an object.

Thermal Energy

Temperature is not a form of energy

Thermal energy increases when:

KE increases as molecules move faster (speed)

AND when PE increases as the molecules move

farther apart (separation)

Heat is the transfer of energy from

a body of higher temperature to a body of lower temperature. 

Heat is a form of energy so:

It is measured in joules

Heat is a form of energy so:

It is measured in joules

When you add ice to a drink, what is happening? Is the ice cooling the drink or is the drink warming the ice?

Remember the definition of HEAT!

Specific Heat of a substance:

Is the amount of heat needed to raise the temperature of 1 kg of that substance by 1°C.

Specific Heat of a substance:

Is the amount of heat needed to raise the temperature of 1 kg of that substance by 1°C.

Is measured in joules per kilogram per degree Celsius [J/(kg°C)]

Specific Heat of a substance:

Is the amount of heat needed to raise the temperature of 1 kg of that substance by 1°C.

Is measured in joules per kilogram per degree Celsius [J/(kg°C)]

Water = 4,184 [J/(kg°C)] Wood = 1760 [J/(kg°C)] Glass = 664 [J/(kg°C)] Iron = 450 [J/(kg°C)]

Water molecules

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How does water cool things?

When heat is added to water, some of the heat has to break some of the bonds before the molecules can start moving faster.

How does water cool things?

When heat is added to water, some of the heat has to break some of the bonds before the molecules can start moving faster.

In metals, electrons can move freely. When heat is added, no strong bonds have to be broken before the electrons can start moving faster.

How does thermal energy change?

When heat flows into or out of the object.

How does thermal energy change?

When heat flows into or out of the object.

To calculate the change: J = mass (kg) X ∆°C X specific heat or Q = m(Tf –Ti)C Q stands for change in thermal energy.

C stands for the object’s specific heat.

Measuring Specific Heat

A calorimeter is a device that can be used to find the specific heat of a material.

In a calorimeter, an object that has been heated transfers heat to a known mass of water. This continues until the object and the water are the same temperature.

Calorimeter

The thermal energy released by the object equals the thermal energy absorbed by the water.

Cross section of a typical bomb calorimeter

Encyclopædia Britannica, Inc.

Cross section of a typical bomb calorimeterEncyclopædia Britannica, Inc.

Molecules in a substance

Speed up when the slow down when the substance is substance is

so they have so they have

(more or less) kinetic energy

(more or less) kinetic energy

Molecules in a substance

Speed up when the slow down when the substance is substance is

so they have so they have

more kinetic energy less kinetic energy

heated cooled

Thermal Energy

Section 2 Transferring Thermal Energy

Transferring Thermal Energy

Occurs in three ways: Conduction

Convection

Radiation

Transferring Thermal Energy

Occurs in three ways: Conduction when particles of one

substance bump into another substance & transfer kinetic energy

Convection

Radiation

Transferring Thermal Energy

Occurs in three ways: Conduction when particles of one

substance bump into another substance & transfer kinetic energy

Convection by movement of warmer & cooler fluids (liquid or gas) from one place to another

Radiation

Transferring Thermal Energy

Occurs in three ways: Conduction when particles of one

substance bump into another substance & transfer kinetic energy

Convection by movement of warmer & cooler fluids (liquid or gas) from one place to another

Radiation by electromagnetic waves through solids, liquids or gases

Transferring Thermal Energy

When heat is transferred through conduction, thermal energy is transferred from place to place without transferring matter. It is transferred by collisions between particles, not by movement of matter.

Transferring Thermal Energy

The best conductors are metals such as silver, copper & aluminum.

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Transferring Thermal Energy

The best conductors are metals such as silver, copper & aluminum.

Solids are better conductors than liquids which are also better than gases.

Transferring Thermal Energy

The best conductors are metals such as silver, copper & aluminum.

Solids are better conductors than liquids which are also better than gases.

Why is this?

Transferring Thermal Energy

The best conductors are metals such as silver, copper & aluminum.

Solids are better conductors than liquids which are also better than gases.

Why is this? Think about the comparative space

between particles…

Convection

A fluid is a substance that can flow.

Convection

A fluid is a substance that can flow. Their movement from one place to

another creates currents.

Convection

A fluid is a substance that can flow. Their movement from one place to

another creates currents. Currents transfer heat.

Convection

A fluid is a substance that can flow. Their movement from one place to

another creates currents. Currents transfer heat. Rising & sinking action of hot and coldcreates convectioncurrents

Convection

Is different than conduction because it transfers thermal energy by moving particles from one place to another.

Convection

Is different than conduction because it transfers thermal energy by moving particles from one place to another.

Warm particles change places with cooler particles.

Convection

Is different than conduction because it transfers thermal energy by moving particles from one place to another.

Warm particles change places with cooler particles.

In conduction no particles move from place to place.

Radiation

Since there is almost no matter in space, energy travels from the Sun to Earth by radiation.

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Radiation

Since there is almost no matter in space, energy travels from the Sun to Earth by radiation.

Radiation travels through solids, liquids, gases and empty space.

When radiation strikes something,

Three things can happen: Material absorbs It reflects OR It transmits some of the energy

The amount of energy absorbed, reflected, or transmitted …

• Depends upon the type of material:• Light-colors reflect more• Dark colors absorb more• Works best in gases because the extra

space between molecules allows it to travel more easily

Incoming & Outgoing Solar Radiation

(Credit - Steve Ackerman and Tom Whittaker)

Controlling Heat Flow

How do animals control heat flow?

What are some things people use to control heat flow?

Insulator

Is a material in which heat flows slowly.

Insulator

Is a material in which heat flows slowly. Wood Some plastics Fiberglass Air (gases are usually better insulators) Insulators are the opposite of

conductors.

How does a thermos work?

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How does a thermos work?

Has 2 glass walls with a vacuum between layers

Shiny aluminum coating inside & outside very reflective

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Thermal Energy

Section 3 Using heat

Heating Systems

Forced-Air system- common- furnace with ducts and returns

Heating Systems

Forced-Air system- common- furnace with ducts and returns

Radiator – furnace heats tank of water which is carried through pipes (conduction & convection)

Heating Systems

Forced-Air system- common- furnace with ducts and returns

Radiator – furnace heats tank of water which is carried through pipes (conduction & convection)

Electric heating – electrically heated coils in floors and walls (convection)

Solar Heating

Passive Solar Heating

Active Solar Heating

Solar Heating

Passive Solar Heating- Materials absorb heat during the day & then helps warm the house at night

Active Solar Heating

Solar Heating

Passive Solar Heating - Materials absorb heat during the day & then helps warm the house at night

Active Solar Heating – solar collectors absorb radiant energy heating air or water inside which is circulated by a pump to radiators

Thermodynamics…

Is the study of the relationship among thermal energy, heat and work.

First Law of Thermodynamics

The increase of the thermal energy of a system equals the work done on the system plus the heat transferred to the system

[Review open vs. closed system]

Second Law of Thermodynamics

The increase in thermal energy of a cool object equals the decrease in thermal energy of the warm object.

Second Law of Thermodynamics

The increase in thermal energy of a cool object equals the decrease in thermal energy of the warm object.

The second law says that it is impossible for heat to flow from a cool object to a warmer object unless work is done.

How does an internal combustion engine work?

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How does an internal combustion engine work?

Intake stroke – the intake valve opens as the piston moves downward, drawing a mixture of gasoline and air into the cylinder

How does an internal combustion engine work?

Compression stroke – Intake valve closes as the piston moves upward compressing the fuel-air mixture

How does an internal combustion engine work?

Power stroke – a spark plug ignites the fuel-air mixture. As the mixture burns, hot gases expand pushing the piston down

How does an internal combustion engine work?

Exhaust stroke – As the piston moves up, the exhaust valve opens and the hot gases are expelled out of the cylinder.

How does an internal combustion engine work?

Heat movers

If the second law is true, then HOW does a refrigerator work?

Heat movers

If the second law is true, then HOW does a refrigerator work?

Refrigerators contain a liquid coolant which is pumped through an expansion valve & changed into a gas cooling it. As it’s pumped through pipes in the refrigerator it absorbs thermal energy then is sent to a compressor

Heat movers – air conditioner

It’s similar to a refrigerator, except the warm air from the room is forced to pass over tubes containing coolant, then the cool air is forced back into the room. The thermal energy absorbed is transferred to the air outdoors.

Heat movers

Refrigerators and air conditioners are heat engines working in reverse.

They use mechanical energy supplied by the compressor motor to move thermal energy from cooler to warmer areas

How do energy transformations produce heat?

Usually when energy transformations occur, some heat is produced in the form of friction which is then transferred to the surroundings by conduction and convection.

Intake stroke- intake valve opens. Piston moves downward, gas mixture fills cylinder

_________StrokeCompression stroke

__________stroke

Intake stroke- intake valve opens. Piston moves downward, gas mixture fills cylinder

Compression stroke Intake valve closes as the piston moves upward compressing the fuel-air mixture

Power stroke – a spark plug ignites the fuel-air mixture. As the mixture burns, hot gases expand pushing the piston down

Exhaust stroke – As the piston moves up, the exhaust valve opens and the hot gases are expelled out of the cylinder.

Four- stroke Cycle