• Define the following terms• A. Work• B. Kinetic Energy• C. Potential Energy

S-41How is work and energy related?

SPS7 Students will relate transformations and flow of energy within a system

a. Identify energy transformations within a system

Chapter 15 & 16

Energy

How are energy and work related?What factors does the kinetic energy of an object depend on?How is gravitational potential energy determined?

15.1 Energy and Its Forms

• Energy – the ability to do work – Measured in joules (J)

• Work – a transfer of energy

15.1 Energy and Its FormsHow are energy and work related?

15.1 Energy and Its FormsWhat factors does the kinetic energy of an object depend on?

KE = ½mv2

• Kinetic Energy – energy due to motion– Depends on it’s mass and speed– Equation

– KE = kinetic energy in Joules (J)– m = mass in kilograms (kg)– v = speed in meters/second (m/s)– Increases rapidly with speed

• Practice Problem– A 0.10 kg bird is flying at a constant

speed of 8.0 m/s. What is the birds kinetic energy?

– Variables?– Fill in the Equation?– Answer?

15.1 Energy and Its Forms What factors does the kinetic energy of an object depend on?

KE = ½mv2

m = 0.10 kg v = 8.0 m/s

KE = ½(0.10)(8.0)2 KE = 3.2J

• Potential Energy – stored due to position or shape– Stretched rubber band– Book on a shelf– Springs

15.1 Energy and Its FormsHow is gravitational potential energy determined?

15.1 Energy and Its Forms How is gravitational potential energy determined?

PE = mgh 420 ft

• Gravitational Potential Energy – due to height– Depends on it’s mass, height, and gravity– Equation

– PE = potential energy in Joules (J)– m = mass in kilograms (kg)– g = gravity (9.80 m/s2)– Height is measured from any point – so this

value is relative

• Practice Problem– A diver at the top of a 10.0 meter

platform has a mass of 50.0 kg. What is her potential energy?

– Variables?– Fill in the Equation?– Answer?

15.1 Energy and Its Forms How is gravitational potential energy determined?

PE = mgh

h = 10.0 kg m = 50.0 kg

PE = (50.0)(9.80)(10.0) PE = 4900J

• A 2000 kg cruise missile is flying at 245 m/s. How many joules of kinetic energy does it have?

S-42What factors does the kinetic energy of an object depend on?

Can energy be converted from one form to another?

What is the law of conservation of energy?

15.2 Energy Conversion and Conservation

• Energy can be converted from one form to another.

15.2 Energy ConservationCan energy be converted from one form to another?

• Law of Conservation of Energy – energy cannot be created or destroyed– We may lose usable energy due to

friction– Or because of heat– Other energy loses?

15.2 Energy ConservationWhat is the law of conservation of energy?

• When an object falls • It starts with what kind of energy?

– Potential

• Ends with what kind of energy?– Kinetic

• Because of conservation

15.2 Energy ConservationWhat energy conversion takes place as an object falls toward Earth?

PE = KE

• Practice Problem

• At a construction site, a 1.50 kg brick is dropped from rest and hits the ground at a speed of 26.0 m/s. What was the gravitational potential energy of the brick before it was dropped?

• Equation?• Variables?• Fill in Equation?

15.2 Energy ConservationWhat energy conversion takes place as an object falls toward Earth?

PE = KE PE = ½ mv2

m = 1.50 kg v = 26.0 m/s

PE = ½ (1.50)(26.0)2 PE = 507J

• A 65 kg man bungee jumps from a platform that is 120 m in the air.

• A. How much potential energy does he have?

• B. How much kinetic energy will he have at the bottom?

S-43How is gravitational potential energy determined?

• Rocket man has a mass of 75 kg and is flying at 45 m/s and a height of 25 m above the ground.

• A. What is his kinetic energy?

• B. What is his potential energy?

• C. What is his total energy?

S-44How is gravitational potential energy determined?

SPS7 Students will relate transformations and flows of energy within a system

b. Investigate molecular motion as it relates to thermal energy changes in terms of conduction, convection, and radiation.

c. Determine the heat capacity of a substance using mass, specific heat, and temperature.

d. Explain the flow of energy in phase changes through the use of a phase diagram.

16 Thermal Energy and Heat

In what direction does heat flow spontaneously?What is the temperature of an object related to?How is change in temperature related to specific heat?

16.1 Thermal Energy and Matter

• Heat – transfer of thermal energy from one object to another because of temperature differences

• Heat flows spontaneously from hotter objects to colder objects

16.1 Thermal Energy & MatterIn what direction does heat flow spontaneously?

• Temperature – a measurement of how hot or cold something is compared to a reference point– Directly related to the average kinetic

energy of the particles in an object– When something heats up, the particles

move faster– When it cools off, the particles move slower– Energy is transferred by collisions

• Fast particles tend to slow down, and slow ones tend to speed up

16.1 Thermal Energy & MatterWhat is the temperature of an object related to?

Kinetic Energy Applet

• Specific Heat – the amount of energy needed to raise the temperature of one gram of material by one degree Celsius.– The lower the specific heat, the faster

the temperature will rise or fall– Common specific heats

16.1 Thermal Energy & MatterHow is change in temperature related to specific heat?

• The heat energy absorbed by something equals the mass times the specific heat times the change in temperature

• Q = heat energy in joules (J)• m = mass in grams (g)• c = specific heat (J/goC)• T = change in temperature in oC

16.1 Thermal Energy & MatterHow is change in temperature related to specific heat?

Q=mcT

• Practice Problem 1

• An iron skillet has a mass of 500 grams. The specific heat of iron is 0.449 J/goC. How much heat must be absorbed to raise the skillet’s temperature by 95oC?

• Variables?• Filled in Equation?• Answer?

16.1 Thermal Energy & MatterHow is change in temperature related to specific heat?

Q=mcT

m = 500 g c = 0.449 J/goC T = 95oC

Q=(500)(0.449) Q=21327.5 J

• Practice Problem 2

• In setting up an aquarium, the heater transfers 1,200 J of heat to 75 g of water. The specific heat of water is 4.18 J/goC so how much does the water temperature rise?

• Variables?• Filled in Equation?• Answer?

16.1 Thermal Energy & MatterHow is change in temperature related to specific heat?

Q=mcT

Q = 1200J m = 75 g c = 4.18 J/goC

1200=(75)(4.18)T T=3.83oC

• How much energy is absorbed by hot gold (c=.128J/goC) when a 455 g sample is heated from 400oC

to 800oC?

S-45How is change in temperature related to specific heat?

Why is conduction slower in gases than in liquids and solids?

In what natural cycles do convection currents occur?How does an objects temperature affect radiation?

16.2 Heat and Thermodynamics

• Three ways to transfer heat energy• Conduction – two objects must be in

contact– Because of collisions between the

particles– Slower in gases than in liquids

and solids because the particles are farther apart

– Don’t collide as often

16.2 Heat and ThermodynamicsWhy is conduction slower in gas than in a liquid and solids?

– Thermal Conductor (conductor) – transfers energy well

– Thermal Insulator (insulator) – transfers energy poorly

16.2 Heat and ThermodynamicsWhy is conduction slower in gas than in a liquid and solids?

• Convection – transfer of energy when fluids move from one place to another– Fluid – anything that flows– Convection current –

when fluids circulate in a loop as it heats up and cools down

16.2 Heat and ThermodynamicsIn what natural cycles do convection currents occur?

– Natural cycles• Ocean currents• Weather systems • Molten rock in the earth

16.2 Heat and ThermodynamicsIn what natural cycles do convection currents occur?

• Radiation – transfer of energy by waves moving through space– As temperature increases the rate of

radiation increases

16.2 Heat and ThermodynamicsHow does an objects temperature affect radiation?

• A temperature and energy graph shows the relationship between thermal energy and temperature.

16.2 Heat and ThermodynamicsWhat do the different sections of a temperature/energy graph mean?

Solid

Melting or Freezing

LiquidBoiling or

Condensing

Gas