THERMAL ENERGY AND HEAT

Objectives Students will be able to identify and know difference between THERMAL ENERGY, TEMPERATURE, and HEAT. Students will be able to identify the 3 ways heat is transferred. Students will be able to compare different conductors and insulators. Students will be able to compare Celsius and Fahrenheit Scale.

TEMPERATURE The measure of the average kinetic energy of the individual particles in an object. Matter is made up of tiny particles called atoms and molecules. These particles are always in motion even if the object they make up isn’t moving at all. Energy of motion is called kinetic energy, so all particles of matter have kinetic energy. The faster the particles are moving, the more kinetic energy they have.

WATER AND DYE EXPERIMENT Why did the dye in hot water move faster than the dye in cold water? The results have to do with the different temperatures of the water.

Back to Experiment So what explanation would be given if we heated the cold water. Its particles will start moving faster, so their kinetic energy will increase. This means that the temperature of the water will rise.

THERMAL ENERGY The total energy of all the particles. If 2 samples of matter are at the same temperature they do not necessarily have the same total energy.

What is Heat? How is heat transferred? Heat is thermal energy moving from a warmer object to a cooler object. There are 3 ways that heat can move. Conduction Convection Radiation

CONDUCTION Heat conduction or thermal conduction is the transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature, and acts to equalize temperature differences. It is also described as heat energy transferred from one material to another by direct contact.

CONVECTION Convection is the movement of molecules within fluids ( a liquid or a gas); the warm fluid rises and cooler fluids flow in to replace it. This creates a circular flow.

More Convection The wind we feel outside is often the result of convection currents. You can understand this by the winds you feel near an ocean. Warm air is lighter than cold air and so it rises. During the daytime, cool air over water moves to replace the air rising up as the land warms the air over it. During the nighttime, the directions change -- the surface of the water is sometimes warmer and the land is cooler.

RADIATION The transfer of energy by electromagnetic waves. Radiation does not require matter to transfer thermal energy.

Radiation The sun's rays travel in straight lines called heat rays. When it moves that way, it is called radiation. When sunlight hits the earth, its radiation is absorbed or reflected.

Conductors and insulators A conductor is an object that can conduct heat well An insulator is an object that conducts heat poorly.

CONDUCTION If you walked barefoot on a hot beach, your feet heat up because of conduction. Radiation from the sun heated the beach sand. Conduction is your feet and the direct contact with the sand.

Conduction Returning to the example of a camp fire. What happens if we use an old metal hanger to roast marshmallows? As the marshmallows cooks, the fire heats the end of the hanger. If we leave the hanger in the fire long enough, eventually the end we are holding will become too hot for us to handle. This happens despite the fact that this end was never placed into the flames. Heat was transferred from the flames to the metal, and then from molecule to molecule in the hanger via conduction until it reached your sensitive fingers.

Question? What would happen if you had chosen a stick to roast your marshmallows on, instead of a metal hanger?

Conduction Not all objects are good conductors of heat. Though the stick may have caught fire, it would not have conducted the heat to your hand. This is because wood is a very poor heat conductor.

Convection After the atmosphere is warmed by radiation or conduction, the heat is transferred by a third process called convection. Convection is the flow of heat throughout the atmosphere. How does this happens?

Lesson Essential Question: How is energy transferred as heat? Summarizing Strategy: On the following slides, identify whether the statement describes cooking popcorn using conduction, convection, or radiation.

Put oil in the bottom of a pan Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the pan on the stove and turn on the burner to medium heat. Cover the pan with a lid. Periodically shake the pan so the kernels move around in the oil.

And the answer is… Conduction The heat is transferred by direct contact from the pan, to the oil, to the kernels of popcorn.

Microwave a bag of popcorn.

And the answer is… Radiation The kernels are heated by the radiation in the microwave.

Cooking popcorn in a popcorn popper.

And the answer is… Convection The hot air transfers the heat to the cooler kernels, and when enough hot air heats the kernels they pop.