The Movement of The Movement of HeatHeatChapter 4Chapter 4

Lesson 19Lesson 19

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ObjectivesObjectives

SPI: 0507.10.2 Use data from an SPI: 0507.10.2 Use data from an investigation to determine the investigation to determine the method by which heat energy is method by which heat energy is transferred from one object or transferred from one object or material to another.material to another.

The Movement of HeatThe Movement of Heat

You feel the warmth of the sun on your You feel the warmth of the sun on your skin. On a hot day at the beach, the sand skin. On a hot day at the beach, the sand feels hot on your feet. On a cold day, the feels hot on your feet. On a cold day, the air in your room is warmer near the air in your room is warmer near the ceiling than near the floor. ceiling than near the floor.

All these things happen because of the All these things happen because of the movement of heat.movement of heat.

In this lesson, you will learn about the In this lesson, you will learn about the different ways that heat energy can different ways that heat energy can travel. travel.

Understanding Heat Understanding Heat EnergyEnergy

As you have learned, all matter is made up As you have learned, all matter is made up of tiny particles that are always moving.of tiny particles that are always moving.

HeatHeat is the energy of these moving is the energy of these moving particles.particles.

That means heat is That means heat is kinetickinetic energy. energy. Your body is warm because tiny particles Your body is warm because tiny particles

in it move all the time.in it move all the time. When you move and exercise, the particles When you move and exercise, the particles

that make up your body move a bit faster. that make up your body move a bit faster. That makes your body warmer.That makes your body warmer.

The faster the particles in an object move, The faster the particles in an object move, the the warmerwarmer the object will be. the object will be.

Understanding Heat Understanding Heat EnergyEnergy

HeatHeat always flows from a warmer always flows from a warmer material to a cooler material.material to a cooler material.

An object becomes An object becomes hotterhotter if the if the particles in it start to move particles in it start to move fasterfaster..

There are There are three three ways this can ways this can happen.happen.

They are called They are called conduction, conduction, convection,convection, and and radiation.radiation.

ConductionConduction Picture yourself walking barefoot along a Picture yourself walking barefoot along a

beach on a hot summer day. After walking beach on a hot summer day. After walking through the sand for just a little while, your through the sand for just a little while, your feet feel hot. Heat moves from hot sand to the feet feel hot. Heat moves from hot sand to the bottoms of your feet by conduction.bottoms of your feet by conduction.

ConductionConduction is the transfer of heat between is the transfer of heat between objects that touch each other.objects that touch each other.

When two materials have different When two materials have different temperatures, heat energy moves from the temperatures, heat energy moves from the warmer one to the cooler one. warmer one to the cooler one.

In other words, the heat moves from the hot In other words, the heat moves from the hot sand to the cooler bottoms of your feet. sand to the cooler bottoms of your feet.

ConductionConduction

When sand gets hot, the particles that make When sand gets hot, the particles that make it up move or vibrate very fast. They have a it up move or vibrate very fast. They have a lot of energy.lot of energy.

When you walk the particles of your skin When you walk the particles of your skin touch the sand. The particles in the hot sand touch the sand. The particles in the hot sand bump against the particles that make up your bump against the particles that make up your feet.feet.

When this happens, the sand particles When this happens, the sand particles transfer some energy to your skin. Now your transfer some energy to your skin. Now your hand has more energy than it had before and hand has more energy than it had before and it feels hotter.it feels hotter.

ConductionConduction

Since the sand gave away some heat Since the sand gave away some heat energy to your feet, the sand is a energy to your feet, the sand is a tiny bit cooler than it was before you tiny bit cooler than it was before you walked on it.walked on it.

The sand transfers energy to your The sand transfers energy to your skin until the temperatures of both skin until the temperatures of both the sand and your skin are the same.the sand and your skin are the same.

If your foot stayed in contact with If your foot stayed in contact with the sand, soon they both would have the sand, soon they both would have the same temperature.the same temperature.

ConductionConduction

Heating a pot of water on an electric Heating a pot of water on an electric stove is another example of stove is another example of conductionconduction..

HeatHeat moves from the hot coils of the moves from the hot coils of the stove to the metal of the pot touching stove to the metal of the pot touching them.them.

As the bottom of the pot gets hot, heat As the bottom of the pot gets hot, heat moves from the bottom of the pot to the moves from the bottom of the pot to the cold water that is touching the bottom of cold water that is touching the bottom of the pot.the pot.

ConductionConduction

ConvectionConvection

How does water in a pot on a stove get hot How does water in a pot on a stove get hot all over?all over?

Remember, the water at the bottom of the Remember, the water at the bottom of the pot is heated by conduction. Some heat pot is heated by conduction. Some heat moves through the rest of the water by moves through the rest of the water by conduction, as particles bump into each conduction, as particles bump into each other and transfer energy. other and transfer energy.

But the water is also heated by But the water is also heated by convection.convection. Convection Convection is the transfer of energy is the transfer of energy

through a liquid or gas by means of currents.through a liquid or gas by means of currents.

ConvectionConvection

Think again about the pot of water Think again about the pot of water on the stove. The water on the on the stove. The water on the bottom of the pot is in contact with bottom of the pot is in contact with the metal of the hot pot, so the metal of the hot pot, so conduction conduction occurs. This bottom occurs. This bottom layer of water heats up because it layer of water heats up because it touches the metal pot. touches the metal pot.

ConvectionConvection

Warm water is less Warm water is less densedense than cool than cool water. You learned about density in water. You learned about density in Lesson 16.Lesson 16.

This difference in density makes This difference in density makes warmer water warmer water riserise in the pot. in the pot.

Cool water is denser than warm water. Cool water is denser than warm water. This makes cool water This makes cool water sinksink in the pot. in the pot.

As cooler water reaches the bottom, it As cooler water reaches the bottom, it heats up and rises.heats up and rises.

ConvectionConvection Water up at the top is now cooler than the Water up at the top is now cooler than the

water below, so it begins to fall.water below, so it begins to fall. This constant rising and falling of warm and This constant rising and falling of warm and

cool water makes convection currents.cool water makes convection currents. Convection currentsConvection currents transfer heat transfer heat

throughout the water. throughout the water. Convection currents also warm your room. Convection currents also warm your room.

As air near a radiator or a vent is heated, As air near a radiator or a vent is heated, the air rises toward the ceiling. Then the air the air rises toward the ceiling. Then the air cools and sinks. This happens over and cools and sinks. This happens over and over, spreading heat throughout your room.over, spreading heat throughout your room.

ConvectionConvection

ConvectionConvection

Convection currents also move Convection currents also move heatheat through Earth’s through Earth’s atmosphereatmosphere..

Cold air sinks because it is Cold air sinks because it is denserdenser, , and warm air rises because it is less and warm air rises because it is less densedense..

This ongoing cycle produces currents This ongoing cycle produces currents of moving air, which we call of moving air, which we call windswinds..

Convection is responsible for much of Convection is responsible for much of Earth’s Earth’s weatherweather..

ConvectionConvection

RadiationRadiation

In both conduction and convection, In both conduction and convection, particles of matter particles of matter transfer transfer heat energy.heat energy.

The particles can be in a The particles can be in a solidsolid, such as , such as the bottom of a pot.the bottom of a pot.

They can be in a They can be in a liquidliquid, such as the water , such as the water in the pot.in the pot.

Or they can be in Or they can be in gasesgases, such as the air in , such as the air in your room or in Earth’s atmosphere.your room or in Earth’s atmosphere.

However, heat can also be transferred However, heat can also be transferred through through emptyempty space. space.

RadiationRadiation

The transfer of heat through space is called The transfer of heat through space is called radiation.radiation.

That is how heat from the sun, which is millions That is how heat from the sun, which is millions of kilometers from Earth, reaches your skin.of kilometers from Earth, reaches your skin.

The sun’s energy travels as The sun’s energy travels as waveswaves through through space.space.

When the energy in sunlight reaches your skin, When the energy in sunlight reaches your skin, the energy makes particles in your skin move the energy makes particles in your skin move faster.faster.

This movement increases the temperature of This movement increases the temperature of your skin, and you feel the sun’s warmth.your skin, and you feel the sun’s warmth.

RadiationRadiation

1. Which kind of heat transfer 1. Which kind of heat transfer takes place when you put a takes place when you put a

spoon in a cup of soup and the spoon in a cup of soup and the spoon gets hot to the touch?spoon gets hot to the touch?

A. convectionA. convection B. conductionB. conduction C. temperatureC. temperature D. radiationD. radiation

1. Which kind of heat transfer 1. Which kind of heat transfer takes place when you put a takes place when you put a

spoon in a cup of soup and the spoon in a cup of soup and the spoon gets hot to the touch?spoon gets hot to the touch?

B. conductionB. conduction

2. Which kind of heat 2. Which kind of heat transfer can take place transfer can take place

through space?through space?

A. radiationA. radiation B. conductionB. conduction C. convectionC. convection D. temperatureD. temperature

2. Which kind of heat 2. Which kind of heat transfer can take place transfer can take place

through space?through space?

A. radiationA. radiation

3. Which kind of heat 3. Which kind of heat transfer causes wind?transfer causes wind?

A. radiationA. radiation B. conductionB. conduction C. temperatureC. temperature D. convectionD. convection

3. Which kind of heat 3. Which kind of heat transfer causes wind?transfer causes wind?

D. convectionD. convection

4. When sand is heated by 4. When sand is heated by the sun, which kind of heat the sun, which kind of heat

transfer is this?transfer is this?

A. conductionA. conduction B. temperatureB. temperature C. radiationC. radiation D. convectionD. convection

4. When sand is heated by 4. When sand is heated by the sun, which kind of heat the sun, which kind of heat

transfer is this?transfer is this?

C. radiationC. radiation