unit 3 pp #2, #3, and #4 7th grade

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 1 TemperatureChapter 11



• Temperature Conversions A given temperature is represented by different numbers on the three temperature scales.

• You can convert from one temperature scale to another using the equations shown on the next slide.

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To convert Use the equation

°C °F

°F °C

°C K K °C 273

K °C °C K 273

F 95

C

32

C 59

F 32


More About Thermal Expansion

• Expansion Joints on Highways If the weather is very hot, a bridge can heat up enough to expand. As the bridge expands, it is in danger of breaking.

• Expansion joints keep segments of the bridge apart so that they have room to expand without the bridge breaking.

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More About Thermal Expansion, continued• Bimetallic Strips in Thermostats are made

of two metals stacked in thin strips. Because the metals expand at different rates, a strip coils and uncoils in response to changes in temperature, as shown below.

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More About Thermal Expansion, continued• Thermal Expansion in Hot Air Balloons

When a gas is heated its particles have more kinetic energy.

• When air (which is a mixture of gases) inside a hot-air balloon is heated, the air expands.

• As it expands, it becomes less dense than the air outside the balloon. So, the balloon goes up.

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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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Transferred Thermal Energy, continued• Reaching the Same Temperature When

objects that have different temperatures come into contact, energy will always be transferred.

• When objects that are touching have the same temperature, they are at thermal equilibrium and no net change in the thermal energy of either one occurs.

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Section 2 What Is Heat?Chapter 11


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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• 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.

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Greenhouse Effect



• The atmosphere traps the sun’s energy because of greenhouse gases, such as water vapor, carbon dioxide, and methane.

• Some scientists are concerned that high levels of greenhouse gases in the atmosphere may trap too much energy and make Earth too warm.

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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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Heat and Temperature Change, continued• Specific Heat is the amount of energy

needed to change the temperature of 1 kg of a substance by 1°C. The higher the specific heat of something is, the more energy it takes to increase its temperature.

• Most metals have very lower specific heats. On the other hand, the specific heat of water is very high.

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Heat and Temperature Change, continued• Heat, Temperature, and Amount Unlike

temperature, energy transferred between objects can not be measured directly. Instead it must be calculated with the following equation:

heat (J) specific heat (J/kg•°C) mass (kg) change in temperature (°C)

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Heat and Temperature Change, continued• Calculating Heat When the temperature of

an object increases, the value of heat is positive.

• When the temperature of an object decreases, the value of heat is negative.

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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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States of Matter, continued

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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

• Energy and Changes of State As ice is heated, its temperature increases to 0°C.

• As the ice melts, its temperature remains at 0°C even as more energy is added. This added energy changes the arrangement of the molecules in the ice.

• The temperature of the ice remains the same until all of the ice has become liquid water. At that point, the water’s temperature starts to increase.

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Changes of State, continued

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Heat and Chemical Changes

• Heat is involved not only in changes of state, which are physical changes, but also in chemical changes—changes that occur when one or more substances are changed into entirely new substances that have different properties.

• During a chemical change, new substances are formed.

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Heat and Chemical Changes, continued• Food and Chemical Energy Food contains

substances from which your body gets energy.

• Energy that your body can use is released when chemical compounds such as carbohydrates are broken down in your body.

• The energy is released in chemical reactions.

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Heat and Chemical Changes, continued• Calorimeters A calorimeter is a device that

measures heat. When one object transfers thermal energy to another object, the energy lost by one object is gained by the other object.

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The Constant Transfer of Energy

• Energy transfer occurs during most events in the universe.

• Energy Loss During Transfer Energy conversion and transfer are not 100% efficient. This means that some energy is lost, often as heat, during physical and chemical changes.

• Constant Input of Energy Most events in the universe require a constant input of energy to keep going.

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The Constant Transfer of Energy, continued• The Role of Lost Energy On a large scale it

is obvious that when energy is withdrawn from something disorder increases.

• When heat is lost during a transfer, that energy acts to increase the random motion of the particles it comes in contact with.

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unit 3 pp #2, #3, and #4 7th grade

Documents

thermal energy heat

transfer of energy

transfer of thermal

objects temperature

energy of motion

lower kinetic energy

form of thermal energy

total kinetic energy