Chapter Introduction

Lesson 1 Thermal Energy, Temperature, and Heat

Lesson 2 Thermal Energy Transfers

Lesson 3 Using Thermal Energy

Chapter Wrap-Up

1. Temperature is the same as thermal energy.

2. Heat is the movement of thermal energy from a hotter object to a cooler object.

3. It takes a large amount of energy to significantly change the temperature of an object with a low specific heat.

4. The thermal energy of an object can never be increased or decreased.

Do you agree or disagree?

• How are temperature and kinetic energy related?

• How do heat and thermal energy differ?

Thermal Energy, Temperature, and Heat

• thermal energy

• temperature

• heat

Thermal Energy, Temperature, and Heat

- in your own words come up with a definition for each of the words below

• Potential energy is stored energy due to the interaction between two objects.

• The potential energy plus the kinetic energy of an object is the mechanical energy of the object.

Kinetic and Potential Energy

• Every solid, liquid, and gas is made up of trillions of tiny particles that are constantly moving.

• Because particles are in motion, they have kinetic energy.

• The faster particles move, the more kinetic energy they have.

What is thermal energy?

• The greater the average distance between particles, the greater the potential energy of the particles.

• Thermal energy is the sum of the kinetic energy and the potential energy of the particles that make up a material.

What is thermal energy? (cont.)

The potential energy of the soccer ball depends on the distance between the ball and Earth. The potential energy of the particles of matter depends on their distance from one another.

• Mechanical energy describes the energy of one object.

• Thermal energy describes the energy of the particles that make up a solid, liquid, or gas.

What is thermal energy? (cont.)

• Scientists define temperature in terms of kinetic energy.

• Temperature represents the average kinetic energy of the particles that make up a material.

What is temperature?

• The greater the average kinetic energy of particles, the greater the temperature.

• The particles in warmer air move at a greater average speed than the particles in colder air.

What is temperature? (cont.)

• Temperature and thermal energy are related, but they are not the same.

• The particles that make up liquid and solid water have different potential energies and, therefore, different thermal energies.

What is temperature? (cont.)

• Thermometers are used to measure temperature.

• Common temperature scales are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

What is temperature? (cont.)

• The movement of thermal energy from a warmer object to a cooler object is called heat.

• All objects have thermal energy; however, you heat something when thermal energy transfers from one object to another.

• The rate at which heating occurs depends on the difference in temperatures between the objects.

What is heat?

• The greater the distance between two particles or two objects, the greater the potential energy.

• Heat is the movement of thermal energy from a warmer object to a cooler object.

• When thermal energy moves between a material and its environment, the material’s temperature changes.

A. thermal energy

B. potential energy

C. mechanical energy

D. kinetic energy

Because particles are in motion, what type of energy do they have?

A. different thermal energies

B. different temperatures

C. different kinetic energies

D. the same thermal energy

Particles that make up liquid and solid water have different potential energies, and therefore also have which of the following?

Which term refers to the average kinetic energy of the particles that make up a material?

A. heat

B. temperature

C. potential energy

D. thermal energy

1. Temperature is the same as thermal energy.

2. Heat is the movement of thermal energy from a hotter object to a cooler object.

Do you agree or disagree?

• What is the effect of having a small specific heat?

• What happens to a material when it is heated?

• In what ways can thermal energy be transferred?

Thermal Energy Transfers

• radiation

• conduction

• thermal conductor

• thermal insulator

• specific heat

Thermal Energy Transfers

• thermal expansion

• thermal contraction

• convection

• convection current

• Thermal energy is transferred in three ways.

• by radiation

• by conduction

• by convection

How is thermal energy transferred?

• The transfer of thermal energy from one material to another by electromagnetic waves is called radiation.

• Radiation is the only way thermal energy can travel from the Sun to Earth, because space is a vacuum.

• Radiation also transfers thermal energy through solids, liquids, and gases.

Radiation

• When particles with different kinetic energies collide, the particles with higher kinetic energy transfer energy to particles with lower kinetic energy.

• The transfer of thermal energy between materials by the collisions of particles is called conduction.

• Conduction continues until the thermal energy of all particles in contact is equal.

Conduction

• The hot air transfers thermal energy to, or heats, the cool lemonade by conduction.

• Eventually the kinetic thermal energy and temperature of the air and the lemonade will be equal.

Conduction (cont.)

• A thermal conductor is a material through which thermal energy flows easily.

• A thermal insulator is a material through which thermal energy does not flow easily.

Conduction (cont.)

• The amount of thermal energy required to increase the temperature of 1 kg of a material by 1°C is called specific heat.

• Water’s high specific heat helps prevent your body from overheating.

• Changing the temperature of a material with a low specific heat is easier than to change the temperature of a material with a high specific heat.

Conduction (cont.)

In a hot car, the temperature of thermal conductors, such as the safety-belt buckles, increases more quickly than the temperature of thermal insulators, such as the seat material.

Units of heat and thermal energy

• The metric unit for measuring heat is the joule.

• This is the same joule used to measure all forms of energy, not just heat.

Heat and thermal energy

• Thermal energy is often measured in calories.

• One calorie is the amount of energy it takes to raise the temperature of one milliliter of water by one degree Celsius.

Specific Heat

• The specific heat is a property of a substance that tells us how much heat is needed to raise the temperature of one kilogram of a material by one degree Celsius.

Knowing the specific heat of a material tells you how quickly the temperature will change as it gains or loses energy.

Why is specific heat different for different materials?

• Temperature measures the average kinetic energy per particle.

• Energy that is divided between fewer particles means more energy per particle, and therefore more temperature change.

• In general, materials made up of heavy atoms or molecules have low specific heat compared with materials made up of lighter ones.

http://connected.mcgraw-hill.com/

Conduction (cont.)

What does it mean if a material has a low specific heat?

The heat equation

• How much heat is needed to raise the temperature of a 250-liter hot tub from 20°C to 40°C?

Solving Problems

1. Looking for:

– …amount of heat in joules

2. Given:

– V = 250 L, 1 L of water = 1 kg

– Temp changes from 20°C to 40°C

– Table specific heat water = 4, 184 J/kg°C

3. Relationships:

– E = mCp(T2 – T1)

Solving Problems

4. Solution: E = (250L × 1kg/L) × 4,184 J/kg°C (40°C - 20°C)

= 20,920,000 JSig. fig./Sci. not. 20,920,000 J = 2.1 x 107 J

• Thermal contraction is a decrease in a material’s volume when its temperature decreases.

• Thermal expansion is an increase in a material’s volume when its temperature increases.

• Thermal expansion and contraction are most noticeable in gases, less noticeable in liquids, and the least noticeable in solids.

Thermal Expansion and Contraction

Thermal Expansion and Contraction (cont.)

What happens to the volume of a gas when it is heated?

• Convection is the transfer of thermal energy by the movement of particles from one part of a material to another.

• Convection only occurs in fluids.

Convection

convection

from Greek convectionem, means “the act of carrying”

This cycle of cooler water sinking and forcing warmer water upward is an example of convection.

Convection (cont.)

What are the three processes that transfer thermal energy?

• The movement of fluids in a cycle because of convection is a convection current.

• Convection currents circulate the water in Earth’s oceans and other bodies of water.

Convection (cont.)

Convection Currents in Earth’s Atmosphere

• When a material has a low specific heat, transferring a small amount of energy to the material increases its temperature significantly.

• Thermal energy can be transferred through radiation, conduction, or convection.

• When a material is heated, the thermal energy of the material increases and the material expands.

A. convection current

B. specific heat

C. thermal conductor

D. thermal insulator

Which term refers to a material through which thermal energy flows easily?

A. conduction

B. thermal expansion

C. thermal conductor

D. thermal contraction

Which describes an increase in a material’s volume when its temperature increases?

A. convection

B. conduction

C. thermal contraction

D. thermal expansion

What term describes the transfer of thermal energy by the movement of particles from one part of a material to another?

3. It takes a large amount of energy to significantly change the temperature of an object with a low specific heat.

4. The thermal energy of an object can never be increased or decreased.

Do you agree or disagree?

• How does a thermostat work?

• How does a refrigerator keep food cold?

• What are the energy transformations in a car engine?

Using Thermal Energy

• heating appliance

• thermostat

• refrigerator

• heat engine

Using Thermal Energy

5. Car engines create energy.

6. Refrigerators cool food by moving thermal energy from inside the refrigerator to the outside.

Do you agree or disagree?

• Thermostats transform thermal energy into mechanical energy that switch heaters on and off.

• Even though many devices transform energy from one form to another or transfer energy from one place to another, the total amount of energy does not change.

Thermal Energy Transformations

• A device that converts electric energy into thermal energy is a heating appliance.

• Curling irons, coffeemakers, and clothes irons are some examples of heating appliances.

Heating Appliances

A thermostat is a device that regulates the temperature of a system.

Thermostats

thermostat

from Greek therme, meaning “heat”; and statos, meaning “a standing”

• Most thermostats contain a bimetallic coil made of two types of metal joined together and bent into a coil.

• The metal on the inside of the coil expands and contracts more than the metal on the outside of the coil.

• When a room warms or cools, the thermal energy causes the bimetallic coil to uncurl slightly or tighten, which turns the furnace off or on.

Thermostats (cont.)

• A device that uses electric energy to transfer thermal energy from a cooler location to a warmer location is called a refrigerator.

• In a refrigerator, a coolant is pumped through pipes on the inside and the outside of the refrigerator.

Refrigerators

Coolant in a refrigerator moves thermal energy from inside to outside the refrigerator.

The coolant, which begins as a liquid, passes through an expansion valve and cools.

As the cold gas flows through pipes inside the refrigerator, it absorbs thermal energy from the refrigerator compartment and vaporizes.

• A heat engine is a machine that converts thermal energy into mechanical energy.

• When a heat engine converts thermal energy into mechanical energy, the mechanical energy moves the vehicle.

• Most cars, buses, boats, trucks, and lawn mowers use a type of heat engine called an internal combustion engine.

Heat Engines

Internal Combustion Engine

Internal Combustion Engine

Heat Engines (cont.)

What is one form of energy that is output from a heat engine?

• A bimetallic coil inside a thermostat controls a switch that turns a heating or cooling device on or off.

• A refrigerator keeps food cold by moving thermal energy from the inside of the refrigerator out to the refrigerator’s surroundings.

• In a car engine, chemical energy in fuel is transformed into thermal energy. Some of this thermal energy is then transformed into mechanical energy.

A. thermostats

B. refrigerators

C. heat engines

D. heating appliances

Curling irons, coffeemakers, and clothes irons are some examples of what?

A. water

B. ice

C. coolant

D. bimetallic coil

Which is pumped through pipes on the inside and the outside of a refrigerator?

A. heat engine

B. heating appliance

C. refrigerator

D. thermostat

Which term refers to a device that regulates the temperature of a system?

5. Car engines create energy.

6. Refrigerators cool food by moving thermal energy from inside the refrigerator to the outside.

Do you agree or disagree?

Key Concept Summary

Interactive Concept Map

Chapter Review

Standardized Test Practice

Thermal energy can be transferred by conduction, radiation, and convection. Thermal energy also can be transformed into other forms of energy and used in devices such as thermostats, refrigerators, and automobile engines.

• The temperature of a material is the average kinetic energy of the particles that make up the material.

• Heat is the movement of thermal energy from a material or area with a higher temperature to a material or area with a lower temperature.

• When a material is heated, the material’s temperature changes.

Lesson 1: Thermal Energy, Temperature, and Heat

Lesson 2: Thermal Energy Transfers

• When a material has a low specific heat, transferring a small amount of energy to the material increases its temperature significantly.

• When a material is heated, the thermal energy of the material increases and the material expands.

• Thermal energy can be transferred by conduction, radiation, or convection.

• The two different metals in a bimetallic coil inside a thermostat expand and contract at different rates. The bimetallic coil curs and uncurls, depending on the thermal energy of the air, pushing a switch that turns a heating or cooling device on or off.

• A refrigerator keeps food cold by moving thermal energy from inside the refrigerator out to the refrigerator’s surroundings.

• In a car engine, chemical energy in fuel is transformed into thermal energy. Some of this thermal energy is then transformed into mechanical energy.

Lesson 3: Using Thermal Energy

A. heat

B. temperature

C. thermal energy

D. mechanical energy

Which describes the sum of the kinetic energy and the potential energy of the particles that make up a material?

A. conduction

B. radiation

C. specific heat

D. thermal expansion

The transfer of thermal energy from one material to another by electromagnetic waves is called what?

A. conduction

B. radiation

C. thermal contraction

D. thermal expansion

Which refers to a decrease in a material’s volume when its temperature decreases?

A. thermal expansion

B. specific heat

C. convection

D. conduction

Which describes the amount of thermal energy required to increase the temperature of 1 kg of a material by 1°C?

A. coolant

B. piston

C. bimetallic coil

D. heat engine

What term refers to the part of a thermostat that expands and contracts to turn a furnace on and off?

A. temperature

B. heat

C. potential energy

D. kinetic energy

What term refers to the movement of thermal energy from a warmer object to a cooler object?

A. convection current

B. thermal contraction

C. thermal conductor

D. thermal insulator

Which term refers to a material through which thermal energy does not flow easily?

A. convection current

B. thermal contraction

C. thermal expansion

D. thermal conductor

Which is the movement of fluids in a cycle because of convection?

A. convection

B. conduction

C. thermal expansion

D. thermal contraction

Which term describes the transfer of thermal energy between materials by the collisions of particles?

A. piston

B. thermostat

C. heat engine

D. heating appliance

Which describes a machine that converts thermal energy into mechanical energy?