Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 1 Temperature Objectives Define temperature in terms of the average kinetic energy

Copyright © by Holt, Rinehart and Winston. All rights reserved.

Section 1 Temperature

Objectives• Define temperature in terms of the average

kinetic energy of atoms or molecules.

• Convert temperature readings between the Fahrenheit, Celsius, and Kelvin scales.

• Recognize heat as a form of energy transfer.

Chapter 13


Temperature and Energy• Temperature is a measure of how hot (or cold)

something is.

• Specifically, it is a measure of the average kinetic energy of the particles in an object. As the average kinetic energy of an object increases, its temperature will increase.

• A thermometer is an instrument that measures and indicates temperature.

Chapter 13 Section 1 Temperature


Measuring TemperatureChapter 13 Section 1 Temperature


Temperature and Energy• Fahrenheit and Celsius are common scales

used for measuring temperatures.

• On the Fahrenheit scale, water freezes at 32ºF and boils at 212ºF.

• The Celsius scale, which is widely used in science, gives a value of 0ºC to the freezing point of water and a value of 100ºC to the boiling point of water at standard atmospheric pressure.



Temperature and EnergyFahrenheit-Celsius Conversion Equations

A degree Celsius is 1.8 times as large as a degree Fahrenheit. Also, the temperature at which water freezes differs for the two scales by 32 degrees.

TF 1.8t 32.0 t TF – 32.0

1.8TF = Fahrenheit temperature t = Celsius temperature



Temperature and Energy

Celsius-Kelvin Conversion Equation

T = t + 237

T = Kelvin temperaturet = Celsius temperature

• The Kelvin scale is based on absolute zero.

• Absolute zero is the temperature at which molecular energy is at a minimum (0 K on the Kelvin scale or –273.16ºC on the Celsius scale).



Temperature ScalesChapter 13 Section 1 Temperature


Math Skills

Temperature Scale Conversion The highest atmospheric temperature ever recorded on Earth was 57.8ºC. Express this temperature both in degrees Fahrenheit and in kelvins.

1. List the given and the unknown values.Given:

Unknown:



Relating Temperature to Energy Transfer• Temperature changes indicate an energy transfer.

• Heat is the energy transferred between objects that are at different temperatures.• The transfer of energy as heat always takes place from a

substance at a higher temperature to a substance at a lower temperature.

• For example, if you hold a glass of ice water in your hands, energy will be transferred as heat from your hand to the glass.



Temperature and HeatChapter 13 Section 1 Temperature


Section 2 Energy Transfer

Objectives

• Investigate and demonstrate how energy is transferred by conduction, convection, and radiation.

• Identify and distinguish between conductors and insulators.

• Solve problems involving specific heat.

Chapter 13


Methods of Energy Transfer

The transfer of heat energy from a hot object can occur in three ways:

• Thermal conduction is the transfer of energy as heat through a material.

• Convection is the movement of matter due to differences in density that are caused by temperature variations.

• Radiation is the energy that is transferred as electromagnetic waves, such as visible light and infrared waves.

Section 2 Energy TransferChapter 13


Methods of Energy Transfer, continued


Thermal Conduction• Conduction involves objects in direct contact.• Conduction takes place when two objects that are in

contact are at unequal temperatures.

Chapter 13




Convection• Convection results from the

movement of warm fluids. • During convection, energy

is carried away by a heated fluid that expands and rises above cooler, denser fluids.

• A convection current is the vertical movement of air currents due to temperature variations.

Chapter 13




Radiation• Radiation is energy transferred as heat in the

form of electromagnetic waves.

• Unlike conduction and convection, radiation does not involve the movement of matter.

• Radiation is therefore the only method of energy transfer that can take place in a vacuum.

• Much of the energy we receive from the sun is transferred by radiation.

Chapter 13


Comparing Convection, Conduction, and Radiation



Conductors and Insulators

• Any material through which energy can be easily transferred as heat is called a conductor.

• Poor conductors are called insulators.

• Gases are extremely poor conductors.

• Liquids are also poor conductors.

• Some solids, such as rubber and wood, are good insulators.

• Most metals are good conductors.



Specific Heat

• Specific heat describes how much energy is required to raise an object’s temperature.

• Specific heat is defined as the quantity of heat required to raise a unit mass of homogenous material 1 K or 1°C in a specified way given constant pressure and volume.

Specific Heat Equationenergy = (specific heat) (ms) (temperature change)

energy = cmt




Math Skills

Specific Heat How much energy must be transferred as heat to the 420 kg of water in a bathtub in order to raise the water’s temperature from 25°C to 37°C?

1. List the given and the unknown values.Given:/kg• K (from table in textbook)Unknown: energy = ? J



Section 3 Using Heat

Objectives

• Describe the concepts of different heating and cooling systems.

• Compare different heating and cooling systems in terms of their transfer of usable energy.

• Explain how a heat engine uses heat energy to do work.

Chapter 13


Heating and Cooling

• Heating a house in the winter, cooling an office building in the summer, or preserving food throughout the year is possible because of machines that transfer energy as heat from one place to another.

• These machines operate with two principles about energy that you have already studied:• The first law of thermodynamics states that the total energy used

in any process—whether that energy is transferred as a result of work, heat, or both—is conserved.


• The second law of thermodynamics states that the energy transferred as heat always moves from an object at a higher temperature to an object at a lower temperature.

Chapter 13



One example is an air conditioner. An air conditioner does work to remove energy as heat from the warm air inside a room and then transfers the energy to the warmer air outside the room.

Air ConditionerChapter 13


Heating SystemsMost heating systems use a source of energy to raise the temperature of a substance such as air or water.


• The human body is a heating system. Some of the energy from food is transferred as heat to blood moving throughout the human body to maintain a temperature of about 37°C (98.6°F).

• In central heating systems, heated water or air transfers energy as heat.

• Solar heating systems also use warmed air or water.

Chapter 13


Heating Systems, continued

• In the solar system shown here, a solar collector uses panels to gather energy radiated by the sun.

• This energy is used to heat water that is then moved throughout the house.

• This is an active solar heating system because it uses energy from another source, such as electricity, to move the heated water.

Section 3 Using HeatChapter 13



• In a passive solar heating system, energy transfer is accomplished by radiation and convection.

• In this example, energy from sunlight is absorbed in a rooftop panel.

• Pipes carry the hot fluid that exchanges heat energy with the air in each room.



Heating SystemsSection 3 Using HeatChapter 13



• When energy can be easily transformed and transferred to accomplish a task, such as heating a room, we say that the energy is in a usable form.

• After this transfer, the same amount of energy is present, according to the law of conservation of energy. Yet less of it is in a form that can be used.

• In general, the amount of usable energy always decreases whenever energy is transferred or transformed.

• Insulation minimizes undesirable energy transfers.



Cooling Systems

• In all cooling systems, energy is transferred as heat from one substance to another, leaving the first substance with less energy and thus a lower temperature.

• A refrigerant is a material used to cool an area or an object to a temperature that is lower than the temperature of the environment. During each operating cycle, the refrigerant evaporates into a gas and then condenses back into a liquid.



RefrigerationSection 3 Using HeatChapter 13


Heat Engines

• A heat engine is a machine that transforms heat into mechanical energy, or work.

• Internal combustion engines burn fuel inside the engine.

• An automobile engine is a four-stroke engine, because four strokes take place for each cycle of the piston.

• The four strokes are called intake, compression, power, and exhaust strokes.

• Internal combustion engines vary in number of pistons.




Internal Combustion EngineChapter 13

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Copyright © by Holt, Rinehart and Winston. All rights reserved. Section 1 Temperature Objectives Define temperature in terms of the average kinetic energy