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Section 1 Temperature

What Is Temperature?

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

• Kinetic energy is the energy of motion. All moving objects have kinetic energy.

• The amount of kinetic energy that an object has depends on the object’s mass and speed.

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What Is Temperature?, continued

• Temperature and Kinetic Energy All matter is made of atoms or molecules that are always moving.

• The faster the particles are moving, the more kinetic energy they have. The more kinetic energy the particles of an object have, the higher the temperature of the object is.

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• The gas particles on the right have a higher average kinetic energy than those on the left. So, the gas on the right is at a higher temperature.

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• Average Kinetic Energy of Particles The motion of particles in matter is random, so individual particles have different amounts of kinetic energy.

• When you measure an object’s temperature, you are measuring the average kinetic energy of the particles in the object.

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Measuring Temperature

• Using a Thermometer Thermometers can measure temperature because of a property called thermal expansion.

• Thermal expansion is the increase in volume of a substance in response to an increase in temperature. As a substance’s temperature increases, its particles move faster and spread out.

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Measuring Temperature, continued

• Temperature Scales Three common temperature scales are the Celsius scale, the Fahrenheit scale, and the Kelvin scale.

• The Kelvin scale is the official SI temperature scale.

• The lowest temperature on the Kelvin scale is 0 K, which is called absolute zero.

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Section 2 What Is Heat?

Transferred Thermal Energy

• Heat is the energy transferred between objects that are at different temperatures.

• When two objects at different temperatures come into contact, energy is always transferred from the object that has the higher temperature to the object that has the lower temperature.

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Transferred Thermal Energy, continued

• Heat and Thermal Energy Heat is transferred in the form of thermal energy. Thermal energy is the total kinetic energy of the particles that make up a substance.

• Thermal energy depends partly on temperature. Thermal energy also depends on how much of a substance there is.

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Conduction, Convection, and Radiation

• Thermal Conduction is the transfer of thermal energy from one substance to another through direct contact. Conduction can also occur within a substance.

• The particles of substances as different temperatures have different average kinetic energies. When such substances touch, their particles collide.

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Conduction, Convection, and Radiation, continued

• When particles collide, particles with higher kinetic energy transfer energy to those with lower kinetic energy.

• This transfer of energy happens until all particles have the same average kinetic energy. As a result, the substances have the same temperature.

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• Conductors and Insulators Substances that conduct thermal energy well are called thermal conductors. Most metals are thermal conductors.

• Substances that do not conduct thermal energy well are called thermal insulators. Wood and plastic are examples of thermal insulators.

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• Convection is the transfer of thermal energy by the movement of a liquid or a gas.

• As water is heated, it becomes less dense. The warmer water rises through the cooler water above it.

• At the surface, the warm water cools and becomes more dense. The cooler water then sinks to the bottom and the cycle repeats.

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• Radiation is the transfer of energy by electromagnetic (EM) waves. All objects radiate EM waves.

• Unlike conduction and convection, radiation can involve either a transfer of energy between particles of matter or an energy transfer across empty space.

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Heat and Temperature Change

• Thermal Conductivity is the rate at which a substance conducts thermal energy.

• Because of its high thermal conductivity, metal transfers energy more rapidly than cloth does.

• If a piece of metal and a piece of cloth are left in sunlight and are at the same high temperature, the metal will feel hotter when touched.

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Section 3 Matter and Heat

States of Matter

• The states of matter are the physical forms in which a substance can exist.

• Three familiar states of matter are solid, liquid, and gas.

• The state a substance is in depends on the speed of its particles, the attraction between them, and the pressure around them.

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Changes of State

• A change of state is a change of a substance from one state of matter to another.

• Changes of state include freezing (liquid to a solid), melting (solid to liquid), boiling (liquid to gas), and condensing (gas to liquid).

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Changes of State, continued

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