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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.
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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 • Combustion-chemical change that gives off heat and light. • Conduction-energy transfer by contact between particles. • Convection-energy transfer by the movement of a large mass of liquid or gas. • Expansion-an increase in the size of an object. • Heat-amount of energy transferred from one object or place to another
Specific Heat-A material’s ability to take in or give off heat. • Insulator-Object or material that prevents conduction. • Kinetic Energy-The particles of matter are in constant motion. • Radiation-Transfer of energy as waves. • 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 Heat 1. Electrical Energy- A. Toasters B. Irons C. Light Bulbs
3. Mechanical Energy-Friction (two objects in motion that are in contact).
3 Types of Heat Transfer • Conduction • Convection • 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 • Air is heated by the radiator. • Hot air is less dense than cold air and rises. • As the hot air mixes with cool air it cools and falls. • The cooler air sinks to the floor and is pushed toward the radiator for reheating by a current of air.
Other Convection Examples: • Earth’s Tectonic Plates • Atmospheric Currents • 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.
