Energy

7a. Designing a diagram, model or analogy to show or describe the motion of molecules for a material in a warmer and cooler state.

7b. Explaining the difference among conduction, convection, and radiation and creating a diagram how heat energy travels in different directions and through different materials by each of these methods.

Vocabulary

1. Combustion-chemical change that gives off heat and light.

2. Conduction-energy transfer by contact between particles.

3. Convection-energy transfer by the movement of a large mass of liquid or gas.

4. Expansion-an increase in the size of an object.

5. Heat-amount of energy transferred from one object or place to another

6. Specific Heat-A material’s ability to take in or give off heat.

7. Insulator-Object or material that prevents conduction.

8. Kinetic Energy-The particles of matter are in constant motion.

9. Radiation-Transfer of energy as waves.

10. Temperature-measure of the average kinetic energy of matter.

Temperature

• Temperature measures how fast the particles are moving.

• Heating a substance makes its particles move faster.

• Cooling a substance makes its particles slow down.

Heat

• More heat can be transferred from a larger object than a smaller object at the same temperature.

• A calorie is a unit for measuring heat. A calorie is amount of heat needed to raise 1 gram of water 1 degree Celsius.

Specific Heat

• Water has a high specific heat. It takes in and gives off heat very slowly.

Specific Heat Examples

• A lake’s large mass and water’s high specific heat prevent the lake’s temperature from changing quickly.

• Iron and Aluminum have low specific heats. Because they heat up quickly, they make good cooking utensils.

Producing Heat

• A heat source is anything that gives off heat.• Most forms of energy produce heat.• Heat moves from regions of high temperature

to regions of low temperature.

Forms of Energy that Produce Heat1. Electrical Energy-

A. Toasters

B. Irons

C. Light Bulbs

2. Chemical Energy-Combustion of wood, oil, gas.

3. Mechanical Energy-Friction (two objects in motion that are in contact).

3 Types of Heat Transfer

1. Conduction

2. Convection

3. Radiation

Conduction

• Objects are in direct contact. • The hot object transfers heat to the cold object.• The fast moving particles in the hot object

bump into the particles in the cold object and make them move faster.

Conduction Examples

• Metals such as aluminum and copper are good conductors of heat.

• Cloth, wood, and plastic are not good conductors. Poor conductors are insulators.

Convection

• Mass of liquid or gas moves.• The material flow is a convection current.• Most air and water currents are convection currents.• A temperature difference between two places causes a

convection current.

Convection Current Example:Heating a room in winter

1. Air is heated by the radiator.

2. Hot air is less dense than cold air and rises.

3. As the hot air mixes with cool air it cools and falls.

4. The cooler air sinks to the floor and is pushed toward the radiator for reheating by a current of air.

Other Convection Examples:

1. Earth’s Tectonic Plates

2. Atmospheric Currents

3. Lake Turnover

2. Air Currents

3. Lake Turnover

Radiation

• Transfer of energy through waves.

Radiation

• Materials with dark colors absorb more radiant heat.

• Light colors reflect

radiant energy. Air and glass allow radiation to pass through.

Radiation Example

• On a cold winter day, the sun shines through a window and warms you.

• The outside air and the window remain cold because the radiant energy pass through them without warming them.

Expansion and Contraction

• Almost all materials take up more space when heated and less space when cooled.

• The Golden Gate Bridge is 1.5 meters longer during the summer than it is during the winter.

Water

• Cooled water contracts until it reaches 4 degrees Celsius.

• Below this temperature, water expands until it freezes at 0 degrees C.

Water

• The expansion makes ice less dense than water. So ice floats in water.