Energy Transfer

THERMAL ENERGY  All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules in constant motion. Because of this constant motion, all atoms have thermal (heat) energy. Whenever a substance is heated, the atoms move faster and faster. When a substance is cooled, the atoms move slower and slower. The "average motion" of the atoms that we sense is what we call temperature.

THERMAL ENERGY  Temperature and heat ARE NOT technically the same thing. Temperature is the average motion of atoms and molecules. Heat is the energy that flows due to temperature differences. Heat is always transferred from warmer to cooler substances.  There are three ways energy transfer can take place. These ways include conduction, convection, and radiation.

METHODS OF ENERGY TRANSFER  Conduction: heat transfer through matter  For this method of heat transfer, it requires objects to come into direct contact

CONDUCTION Have you ever touched a pan on the stove and got burned? That was thanks to conduction. Takes place when 2 objects in contact are at unequal temperatures Remember: Energy transfer always takes place from warmer to cooler substances.

CONVECTION  Convection: heat transfer by the movement of mass from one place to another; it can only take place in liquids and gases

CONVECTION  Involves the movement of the heated substance itself  Convection is only possible if it is a fluid (liquid or gas) because the particles within solids are not as free to move

CONVECTION CURRENT Convection Current: the flow of a fluid due to heated expansion followed by cooling and contraction g.com/media/item.action? quick=12p g.com/media/item.action? quick=12p g.com/media/item.action? quick=12p g.com/media/item.action? quick=12p

CONVECTION CURRENTS  Heating and cooling of a building involves convection currents: warm air expands and rises from vents near the floor; it then cools and contracts near the ceiling & sinks back to the floor

RADIATION  Radiation: the transfer of energy by electromagnetic waves  A hot object radiates more energy than a cool object.

RADIATION  Radiation is different from conduction and convection because it does not involve the movement of matter; and, it is the only way heat is transferred that can move through empty space

METHODS OF COOKING POPCORN: CONDUCTION, CONVECTION, OR RADIATION? 1. Obtain a popcorn popper. Place the popcorn kernels in the popper. Plug in/turn on the popper. Hot air will transfer heat to the kernels, making them expand and pop. 2. 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. 3. Microwave a bag of microwave popcorn. #1: Convection, #2: Conduction, #3: Radiation

CONDUCTION, CONVECTION, & RADIATION

CONDUCTORS AND INSULATORS  Conductor: a material through which energy can be easily transferred as heat.  Gases are poor conductors because their particles are far apart and the particle collisions necessary for energy transfer rarely occur.

GOOD CONDUCTORS  Good conductors: metals such as copper and silver, along with  gold  aluminum  iron  steel  brass  bronze  mercury  graphite  dirty water  concrete

BAD CONDUCTORS  Bad Conductors: Certain solids like rubber and wood  glass  oil  asphalt  fiberglass  porcelain  ceramic  quartz  (dry) cotton  (dry) paper  plastic  air  diamond  pure water

INSULATOR  Insulator: a material that is a poor energy conductor  Good insulator: wood

THESE ARE PICTURES OF CONDUCTORS AND INSULATORS Conductors Insulators