Heat and Technology

Bellringer The temperature of boiling water is 100° on the Celsius scale and 212° on the Fahrenheit scale. Look at each of the following temperatures and decide whether you think that it is hot or cold: 60°F60°C37°F37°C0°C100°F70°F Write your responses in your science journal.

What Is Temperature? Temperature is a measure of the average kinetic energy of the particles in an object.

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.

What Is Temperature?, continued 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.

Measuring Temperature Using a Thermometer Thermometers can measure temperature because of thermal expansion. Thermal expansion is the increase in volume of a substance in response to an increase in temperature.

Measuring Temperature, continued Temperature Scales : Celsius scale Fahrenheit scale Kelvin scale - official SI temperature scale The lowest temperature on the Kelvin scale is 0 K, which is called absolute zero.

Measuring Temperature, continued To convert Use the equation °C  °F °F  °C °C  K K  °C  273 K  °C  273 K  °C K  °C °C  K  273

Bellringer You walk into the bathroom in your bare feet. The temperature in there is 23°C. You step onto the tile floor, and it feels very cold. Quickly, you step onto a throw rug, and the rug feels warmer. Is the floor really colder than the rug? Why do they seem to be at different temperatures when your bare feet touch them? Write your answers in your science journal.

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.

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.

Conduction, Convection, and Radiation Thermal Conduction is the transfer of thermal energy from one substance to another through direct contact. The particles of substances as different temperatures have different average kinetic energies. When such substances touch, their particles collide.

Conduction, Convection, and Radiation, continued 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.

Conduction, Convection, and Radiation, continued 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.

Conduction, Convection, and Radiation, continued 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.

Conduction, Convection, and Radiation, continued Radiation and the Greenhouse Effect Earth’s atmosphere allows the sun’s visible light to pass through it. The atmosphere also traps energy, too. This process is called the greenhouse effect. Without the greenhouse effect, Earth would be a cold, lifeless planet.

Greenhouse Effect Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

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.

Bellringer Predict what changes would occur if you added an equal number of ice cubes to a glass of cold water and a glass of warm water. Explain your answer in your science journal.

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

States of Matter, continued

Changes of State A change of state is a change of a substance from one state of matter to another. freezing (liquid to a solid), melting (solid to liquid), boiling (liquid to gas), condensing (gas to liquid).

Changes of State, continued

Bellringer Predict whether leaving the refrigerator door open on a hot summer day will help to cool the kitchen. Explain your answer in your science journal.

Heating Systems Hot–Water Heating The high specific heat of water makes it useful for heating systems.

Heating Systems, continued Warm–Air Heating Air cannot hold as much energy as water can. But warm–air heating systems are used in many homes and offices in the United States.

Heating Systems, continued Insulation is a material that reduces the transfer of thermal energy. When insulation is used in walls, ceilings, and floors, less heat passes into or out of the building. Solar Heating The sun gives off a huge amount of energy. Solar heating systems use this energy to heat houses and buildings.

Section 4 Heat Technology Chapter M6