3.1.2 (KE & PE) & 3.1.1 (Thermal) Notes Name/Date: _____________________

Chapter 15.1 Energy and Its Forms (p. 446)Energy - ability to do work

Includes kinetic, sound, gravitational potential, elastic potential, light, electrical, chemical, thermal, magnetic and nuclear energy

Measured in joules (J)Kinetic energy-energy in the form of motion

Kinetic energy depends on mass and speed The greater the mass a moving object has=the more kinetic energy The greater an object’s velocity=the more kinetic energy it has

KE = ½ mv2 m = mass v = velocityExample: For a car: velocity = 4 m/s mass = 1000 kg

KE = (0.5) (1000 kg) (4 m/s)2

KE = 8,000 J

For a car: velocity = 8 m/s mass = 1000 kg

KE = (0.5) (1000 kg) (8 m/s)2

KE = 32,000 J

Doubled the velocity but quadrupled the KE; makes the car 4 times as hard to stop

Potential energy-stored energy Amount on potential energy an object has depends on its position or shape i.e. object on a ledge above a reference point, a compressed spring, or a

stretched rubber bandGravitational potential energy – potential energy that depends upon an object’s height

Increases when an object is raised to a higher level PE = mgh m = mass (in kg) g = acceleration due to gravity

(9.8 m/s2) h = height (in meters)Example: Diver at the top of the diving board

PE = mgh = (50kg)(9.8 m/s2)(10 m) = 4900 J

Diver on the groundPE = mgh = (50kg)(9.8 m/s2)(0 m) = 0 J

Gravitational potential energy converts to kinetic energy as the object fallsElastic potential energy – potential energy of an object that is stretched or compressed (p. 450)

Something is elastic if it springs back to its original shape after it is stretched or compressed

Examples include: rubber bands, springsThermal energy – total potential and kinetic energy of all the microscopic particles in an object (p. 451)

When an object’s atoms move faster, its thermal energy increases and the object becomes warmer

Extremely hot objects omit lightChemical energy – energy stored in chemical bonds (p. 451)

For example: when wood is burned, it emits heat and light Chemical energy is stored in the wood itself When the bonds are broken, the released energy can do work All chemical compounds – especially fuels such as coal and gasoline store

energyElectrical energy – energy associated with electric charges (p. 452)

Electricity = electrical energy Used to run lots of devices Lightning is a natural example

Nuclear energy – energy stored in atomic nuclei (p. 452) Nuclear fission – the splitting of nuclei

o runs nuclear power plants Nuclear fusion – the combining of nuclei

o which the sun uses to produce heat and lightChapter 15.2 Energy ConversionMechanical energy-the total amount of kinetic and potential energy in a system

ME = PE + KEEnergy can be converted from one form to another

Example: wind-up toys store potential energy in a compressed spring When the spring unwinds, elastic potential energy is converted into the

kinetic energy that makes the toy move Another example: A falling ball loses gravitational potential energy but

gains an equal amount of kinetic energyFirst Law of Thermodynamics - energy cannot be created or destroyed but it can be changed in form

Called the Law of conservation of energy In a closed system (where nothing can enter or leave) = the amount of energy in

the beginning must equal the amount of energy at the endEnergy conversion in pendulums:

1. Where is the greatest potential energy?2. Where is the greatest kinetic energy?

Chap 16.1 Thermal energy and matter (p. 474)Heat - transfer of thermal energy from one object to another because of a temperature difference

Always flows spontaneously from hot objects to cold objects Energy will not spontaneously flow from a lower temperature to a higher

temperature Measured in joules (4.18605 J = 1 calorie) Measured indirectly through changes in temperature (i.e. an increase in

temperature indicates an addition of thermal energy through heating)Temperature-a measure of the average kinetic energy of the particles in a sample of matter

When the particles move faster and their average kinetic energy is greater = the temperature of the object rises

When particles move more slowly = the average kinetic energy decreases = the temperature decreases

Measure of how hot or cold an object is compared to a reference point Measured with thermometers Not mass dependent

Thermal energy – total potential and kinetic energy of all the particles in an object Depends on mass, temperature, and phase (solid, liquid or gas) Different kinds of matter have different thermal energies, even when mass and

temperature are the same Mass greater mass (even at the same temp) = greater thermal energy

because there are more particles (i.e. tea cup vs. tea pot) Temperature greater temperature = greater thermal energy (average kinetic

energy of the particles is higher) (i.e. ice tea vs. hot tea) Can’t be measured directlyThermal expansion-when an object gets hotter, it expands

The increased molecular motion during heating causes expansion in solids, liquids, and gases

Thermal contraction-when an object gets cooler, it contracts Slower particles collide less often and exert less force during cooling and

causes contractions Chapter 16.2 Heat and Thermodynamics (p. 479)Conduction-transfer of energy through matter by direct contact of particles

Transfer of thermal energy with no overall transfer of matter (particles remain approximately in place)

Heat may be transferred by conduction through a given material or from one material to another (i.e. a spoon heating up in the boiling water)

Takes place in solids, liquids, and gasesThermal conductors – materials that conduct (transfer) thermal energy well Solids better conductors of heat because their particles are packed closed

together Many metals = good conductors of heat These metals have loosely held electrons that move around easily and transfer

kinetic energy to nearby particles more efficiently Silver, copper, and aluminum = good heat conductors Wood, plastic, glass and fiberglass = poor conductors of heat

Insulators - materials that do not allow heat to move easily through them (i.e. wood, plastic, glass and fiberglass; gases such as air)Examples of materials that trap air: foam cups, down jackets, quilts, double pane windowsBuildings insulated to keep warm air inside during cold weather and outside during warm weatherInsulation above ceilings and in attics because warm air rises due to convection currentsConvection-transfer of thermal energy by the movement of particles from place to place

Convection is the most important way the thermal energy is transferred in fluids (any material that flows, i.e. liquid or gas)

Fluid particles move from one location to another carrying energy with them Fluid particles have more freedom to move and they will expand when heated Convection currents transfer thermal energy from warmer to cooler parts of

the fluid (i.e. heating water on the pot; water becomes hot and rises; this forces the cold water to the bottom; it will then rises as the hot water at the top cooled)

Radiation-transfer of energy in the form of waves moving through space Example: heat lamps used in restaurants; sun; heating coil on the stove Unlike conduction and convection, radiation doesn’t require matter (no air

between sun and Earth but we feel radiant energy everyday) Only radiant energy that is absorb is converted to thermal energy Shiny materials reflect radiant energy Dull materials absorb it Dark colored materials absorb more radiant energy than light colored materials All objects warmer than 0 K (-273oC) emits radiation As an object’s temperature increases, the rate at which it radiates energy

increases

First Law of Thermodynamics – states that energy can never be created or destroyed It can change forms, be stored in different ways and transferred from one place

to another Also known as the law of conservation of energy In a closed system, the internal energy can be changed only by:

1. heat flowing into or out of the system2. the system doing work on an external system or having work done on it by

an external systems Energy is always conserved. In theory, a machine will only produce as much energy as is put into the machine. In fact, whenever a machine is used, some energy is changed to heat due to friction

or heat lost to the environment.

It is impossible to build a machine that does nothing but convert heat into useful work! Some energy will always be lost!

The work put out by a machine is always less than the work put into a machine (No machine is 100% efficient).

Second Law of Thermodynamics – states that thermal energy can flow from colder objects to hotter objects only if work is done on the systemHeat will not spontaneously flow from colder to warmer temperatures!

Example: A cold drink will warm up when left on the counter; the warm air heats up the cold drink

Example: the heat moves from your warm hand to a ice cube (causing the ice to melt)

Example: a refrigerator must do work to transfer thermal energy from the cold food compartment to the warm room air

Summary: KE = ½ mv2 KE= J (all energy measured in J!) m=kg v= m/sPE = mgh PE = J m = kg g = 9.8 m/s2 h = m

Samples:1. The sign says, “Watch for falling rock.” A 5kg rock sits on the edge of a ledge 30m above the roadway. What is the potential energy of the rock on the ledge? A. 735N B. 735J C. 1470N D. 1470J

2. An object w/ a mass of 6kg is traveling 2m/s. What is the object’s kinetic energy? A. 32J B. 12J C. 7J D. 4J

3. An object w/ a mass of 4kg is 15m above the ground. What is the gravitational potential energy? A. 147J B. 153J C. 588J D. 882J

4. If the velocity of an object measuring 45kg changed from 2m/s to 6.5m/s, what is the difference in kinetic energy from before and after this change? A. 860.625J B. 90J C. 385.125J D. 236J

5. A sport utility vehicle (SUV) w/ a mass of 2,450kg is traveling at 21m/s southeast. What is the KE of the SUV?

6. A jet skier w/ a total mass (jet ski + person) of 250kg is traveling south w/ a KE of 40,500J. What is the velocity of the jet skier?

7. A cat with a KE of 160J is climbing up a tree at a velocity of 2m/s. What is the cat’s mass?

8. Austin throws a 0.173kg baseball w/ a velocity of 21m/s. What is the KE of the baseball?

9. A 0.25kg apple hanging from a tree has a PE of 12J. If the apple falls, how far did it fall?

10. Druquelis rolls a bowling ball with a mass of 2kg down lane 15 at 0.5m/s. What is its KE?

11. Karen rolls a bowling ball with a 2kg mass down lane 16 at 0.7m/s. Aisha rolls a 2nd bowling ball with the same mass down lane 17 at 1m/s. Which has the greater kinetic energy? A. the faster ballB. the slower ballC. They have the same mass, so they will have the same KE. D. The length of the lane is needed to assess this.

Summary: Law of conservation of energy = energy changes from one form to another, it is never created or destroyed.Kinetic energy = energy of motion, usually lowest point “bottom of the hill”Potential energy = stored energy, usually highest point “top of a cliff”Gravitational energy = think of a dam or skydivingChemical energy = think of a match or gasolineElectrical energy = think of electricityElastic energy = think spring or rubber bandNuclear energy = think of radioactive elements or the SunThermal energy = think heat, fire, friction (Specific heat, mass and temperature all affect thermal energy)Specific heat = the higher the specific heat the longer it takes to heat or cool, water has a high specific heat, metal usually have a low specific heat, that’s why metal gets hot to touch in the sun but not a puddle of water.

Samples: 1. The law of conservation of energy implies which statement? A. The amount of energy in a closed system remains constant. B. The kinetic energy of a moving object is always equal to its potential energy. C. Light energy is always decreasing. D. Thermal energy is always increasing.

2. Which of the following is a device that transforms mechanical energy into electrical energy? A. blender B. car engine C. hydroelectric dam D. flashlight

3. Which is an example of chemical energy? A. a horse pulling a cart B. a thermos of hot coffeeC. the bonds holding atoms together in food D. a marching band in a parade.

4. Eduardo throws a rock up into the air, which of the following describes the changes in kinetic or potential energy? A. The kinetic energy is increasing as it goes up and decreasing as it falls back down. B. The potential energy is increasing as it goes up and decreasing as it falls back down. C. The potential energy is increasing as it goes up and increasing as it falls back down. D. The kinetic energy is decreasing as it goes up and decreasing as it falls back down.

5. What energy transformation occurs when an unlit match is lit? A. chemical energy to electromagnetic energy B. chemical energy to light energy and heat energy C. Heat energy to light energy D. Light energy to heat energy and chemical energy

6. At which point would there be the greatest kinetic energy?

7. Where would the kids in the picture have the greatest potential energy? A. standing on the ground B. sitting on the bottom of the slide C. climbing halfway up the ladder to the slide D. standing at the top of the slide

8. At which point does the girl have the greatest amount of potential energy?

At which point does the girl have the greatest amount of kinetic energy?

9. Which statement best describes energy as illustrated in the diagram of the coaster? A. PE and KE are both increasing. B. PE and KE are both decreasing. C. PE increases as KE decreases. D. PE decreases as KE increases.

10. Circle the spring that has the greatest potential energy?

11. A ball sits on top of a ramp. Select that statement that correctly describes the changes to the ball’s KE and PE as it rolls down the ramp. A. KE and PE both decrease. B. KE and PE both increase. C. KE decreases and PE increases. D. KE increases and PE decreases.

12. Plants use sunlight to fuel photosynthesis. Which is the best description of the energy transformation involved in this process? A. radiant light energy to thermal energy B. radiant light energy to chemical energy C. thermal energy to mechanical energy

D. thermal energy to chemical energy.

13. Which is a source of PE that could release radiant energy? A. a diamond B. a sunflower seed C. a neutron D. a match

14. A wet cell battery is an example of stored PE. Once connected to a load, the stored energy is converted. Describe the conversion of energy that results in the movement of the hands in a battery-powered clock. A. chemical to electrical to mechanical B. chemical to thermal to electricalC. electrical to thermal to mechanical D. chemical to electrical to thermal

15. Which of the following represents PE but not KE? A. an avalanche B. a coiled springC. a hot air balloon in flight D. the pistons in a working engine

16. Rubi places a message in a bottle and drops it off the side of a mountain, into the ocean. When does the bottle have the greatest KE? A. when Rubi holds the bottle in her hand just before dropping it. B.when it is floating on the water.C. just after Rubi releases the bottle D. Just before the bottle hits the surface of the water.

17. Why does the total energy of a rolling object on a flat surface seem to decrease as it slows down? A. Some energy is destroyed. B. Some energy is wasted b/c of friction. C. Some energy is transformed into potential energy. D. Some energy is transformed into kinetic energy.

Summary:Thermal energy flows hot to cold!Energy will NOT spontaneously flow from cold to hot. Work must be done! (refrigerator)It is impossible to build a machine that is 100% efficient. Most machines are less than 50% efficient due to heat loss.Conduction: b/w solids CONTACTConvection: b/w fluids (liquid or gas) Radiation: waves, doesn’t require matterHeat = total kinetic energyTemperature = measure of the average kinetic energyInsulators = does NOT allow heat to flow easily, (wood, plastic, air)Conductors = allows heat to flow easily (metals)

Samples:

1. Why is it dangerous to leave a child or pet in a locked car with the windows closed in bright sunlight?A. The air in a car w/ closed windows will soon run out of oxygen and asphyxiate the people within.B. The car becomes dangerously cold as it transfer heat energy to the air by radiation.C. The car’s temperature remains equal to the air temperature outside due to a state of equilibrium that could be dangerous.D. The car can absorb enough radiant heat from the sun to make its temp hot enough to be dangerous to a child or pet.

2. The metal handle of a pot on a stove soon becomes too hot to touch. What type of heat transfer causes this?A. conduction B. radiation C. convection D. No heat transfer takes place.

3. Heat transfer always results in a change of temperature when it flowsA. b/w equally cold objectsB. b/w equally warm objectsC. from a colder object to a warmer objectD. from a warmer object to a colder object

4. The type of heat transfer that takes place in fluids isA. conduction B. convection C. radiation D. electromagnetic waves

5. Materials that prevent heat flow areA. usually metals B. conductors C. insulators D. radiators

6. Which is true? A. Temp. measures the average kinetic energy of the molecules of a substance.B. Temp. is inversely proportional to the average kinetic energy of the molecules of a substance.C. Temp. is a measurement of the total energy in a substance.D. Temp. is made up of not only the average kinetic energies of the molecules of the substance, but also the potential energies of the molecules of a substance.

7. A coiled heating element was placed in a calorimeter. When 55kJ of electrical energy was supplied to the coil, it heated up and glowed brightly. 54.2kJ of total heat energy was recorded. Which best explains why the heat energy output was less than the electrical energy input. A. 0.8kJ of energy was stored by the coils as binding energyB. 0.8kJ if energy was converted into a new mass and the coil got heavier.C. The element wasted 0.8kJ of energy by transforming it into light instead of heat.D. 0.8kJ of electrical energy was destroyed by frictions in the coils.

8. Using 15% as a machine’s energy efficiency, what is the actual work output if the total work input is 7500kJ?a. 500kJ b. 750kJ c. 1125kJ d. 7500kJ

9. How is heat energy most likely transferred through a liquid?a. by convection b. by conductionc. by electromagnetic waves d. by radiation

10. In what direction will thermal energy flow? A. from beaker A to beaker BB. from beaker B to beaker AC. From the thermometers to the liquidD. from the thermometers to the beaker

11. In which state of matter are molecules free to move the most?

a. ice b. condensationc. liquid water d. steam

12. A dog is laying on the floor in front of the fireplace. What process moves thermal energy from the fire in the fireplace to the dog on the rug? A. conduction B. convection C. radiation D. fission

13. The diagram illustrates the formations of breezes near large bodies of water. Based on the process illustrated, which of the following methods of heat transfer is involved?A. radiationB. conductionC. convectionD. friction

14. A recently-used hot ceramic teapot is place on a cold trivet. Which statement is correct about the sequence of thermal energy transfers? A. The air transfers energy to the teapot & trivet, and they become cool.B. The teapot transfers all of its energy to the air and becomes cool.C. The teapot transfers some energy to the trivet and some energy to the air and becomes cool.D. The trivet transfers energy to the teapot and the teapot becomes cool.

15. Ashley adds liquid water to an ice tray and places it in the freezer. What happens?A. Thermal energy flows from the higher-energy phase (water) to the lower-energy phase (cold air).

B. Thermal energy flows from the higher-energy phase (cold air) to the lower-energy phase (water).C. Cold radiates from the cold air into the warm water.D. The insulation of the ice tray keeps the temperature from changing much.

16. Which of the following is able to convert all the thermal energy produced into useful work?a. nuclear power reactor b. gasoline engine c. stovetop range d. none of these

17. Heat will transfer from a high temperature to a low temperature by several different methods. The heat transferred by an electric stovetop coil to the teakettle is an example of transfer by a. convection b. conduction c. radiation

18. Energy is not destroyed, but rather converted from one form to another. Describe the conversion of energy in the following process: A power reactor utilizes the process of uranium fission to create electricity.A. nuclear to electricalB. nuclear to thermal to electricalC. nuclear to mechanical to thermal to electricalD. nuclear to thermal to mechanical to electrical