Thermal Energy & EM SPECTRUM Unit 9 Section 1 nOTES 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 kinetic energy in the form of 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.

Thermal energy When the motion of particles (kinetic energy) increases, so does the temperature. When the motion of particles decreases, so does the temperature. The "average motion" of the atoms that we sense is what we call temperature.

Thermal energy

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.

Energy Transfer Fast Slow Heat always moves from a warmer place to a cooler place. “Hot” objects in a cooler room will cool to room temperature and “Cold” objects in a warmer room will heat up to room temperature: known as thermal equilibrium. Hot water Cold water (90. oC) (10. oC) Fast Slow

Glow Stick Demonstration What will happen to the glow stick when it is placed in hot water? What will happen to the glow stick when it is placed in cold water?

Temperature How is temperature measured? Thermometer In order to measure temperature accurately, what physical property is relied upon? Most objects EXPAND when their temperature increases

Temperature Scales The first widely used temperature scale was devised by Gabriel Fahrenheit. Water freezing point: 32F Water boiling point: 212F Another widely used scale was devised by Anders Celsius. Water freezing point: 0C. Water boiling point: 100C

Conversion between Fahrenheit and Celsius Equations: Temperature Scales Conversion between Fahrenheit and Celsius Equations: Example #1: An object has a temperature of 45C. What is its temperature in degree Fahrenheit? 113 F Example #2: The temperature of a winter day is 14F. What is the temperature in degree Celsius? -10 C

Zero Temperature The zero point on the Fahrenheit scale was based on the temperature of a mixture of salt and ice in a saturated salt solution. The zero point on the Celsius scale is the freezing point of water. Both scales go below zero.

Kelvin Temperature Scale Kelvin Scale (Absolute Temperature Scale): Examples: Water freezing point: 0C =273.2 K. Water boiling point: 100C = 373.2 K

Absolute zero Absolute Zero: the coldest possible temperature that can be reached; occurs when there is no more thermal energy in an object. It is not possible to reach absolute zero because you can never remove all of the heat from an object.

Absolute zero

Misconceptions about temperature https://www.youtube.com/watch?v=vqDbMEdLiCs

Methods of Energy Transfer There are three ways energy transfer can take place. They are: conduction, convection, and radiation.

Methods of Energy Transfer Conduction: heat transfer through matter due to a temperature difference For this method of heat transfer, it requires objects to come into direct contact Conduction = 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.

When you heat a metal strip at one end, the heat travels to the other end. As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction

Example of Conduction A piece of cheese melts as heat is transferred from the meat to the cheese (Contact)

Example of Conduction

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 http://www.absorblearning.com/media/item.action?quick=12p

Convection Current and Earth Science

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

Examples of Convection Air movement in a home A pot of heating water

Convection Consider this - when you look at the road in the summertime on a hot day, you may notice that the air above the road looks “blurry” – this is convection taking place as the hot air directly over the road absorbs the heat from the road and rises. Although the explanation can be quite complex, convection can help explain why mirages are seen in the desert.

Question If conduction deals with solids and convection deals with liquids, how does heat arrive to Earth from the Sun? There is very little matter in between the Earth and Sun.

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.

Examples of Radiation Examples of Radiation Fire Heat Lamps Sun

Methods of Cooking Popcorn: Conduction, Convection, or Radiation? 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. 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. 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 http://www.wisegeek.com/what-is-thermal-equilibrium.htm

Review Questions How does the average kinetic energy of an object relate to its temperature? Temperature is proportional to average kinetic energy; as the kinetic energy of an object increases, its temperature will increase.

Review Questions If a cup of coffee and a popsicle were left on the table in this room, what would happen to them? Why? The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature.

Why does hot air rise and cool air sink? Review Questions Why does hot air rise and cool air sink? In warm air, the molecules move apart, so it is less dense and rises. In cooler air, the molecules move closer together, so it is more dense and sinks.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions T or F: Radiation requires particles to travel through. T or F: Radiation travels at the speed of light. T or F: Radiation can travel through a vacuum.

Review Questions Suppose I have 2 objects: a coat and a metal hanger. Both objects were left in this classroom overnight. The temperature of the classroom is 68◦F, therefore, both objects are the same temperature (thermal equilibrium). Why does the hanger feel colder to the touch than the coat?

Review Questions When you hold a piece of ice in your hand, what causes it to melt? The temperature of the ice is lower than your hand; therefore, the molecules in the ice move more slowly than those in your hand. As the molecules on the surface of your hand collide with those of the ice, energy is transferred from your hand to the ice.