Temperature Return to Table of Contents Slide 5 / 112 Sensing - - PDF document

Slide 1 / 112

8th Grade

Thermal Energy

2015-10-09 www.njctl.org

Slide 2 / 112 Temperature, Heat and Energy Transfer

· Temperature · Thermal Energy · Energy Transfer · Specific Heat

Click on the topic to go to that section

· Thermodynamics and Energy Conservation

Slide 3 / 112

Temperature

Return to Table

• f Contents

Slide 4 / 112 Sensing Temperature

It is easy to tell if an

• bject is hot or cold by

touching it. How hot or cold something feels is related to temperature, but only provides a rough indicator. Which of the following do you think is colder, the ice cream or the tea?

Slide 5 / 112 What is Temperature?

To understand temperature, remember that all matter is made

• f molecules that are in constant motion. What kind of energy

do they have if they are in motion? The water molecules in this glass are in constant random motion. Even the molecules in this solid pencil are vibrating relative to a fixed position.

Slide 6 / 112

Temperature and Kinetic Energy

The more kinetic energy molecules have, the higher the temperature. Temperature is directly proportional to the average kinetic energy of an object's molecules.

clip: Indiana University

Slide 7 / 112 Thermal Expansion

As the temperature of a substance increases, its molecules pick up speed and gain kinetic energy.

image: National Oceanography Centre

This increase in kinetic energy causes the molecules to spread farther apart and the substance expands.

Slide 8 / 112 Thermal Contraction

As the temperature of a substance decreases, its molecules slow down and lose kinetic energy. What do you think this decrease in kinetic energy causes? Compare it to what we said about warm molecules.

Slide 9 / 112

Thermal Expansion

Watch this demo of a metal ball and ring to see thermal expansion. Explain what happened to make the ball not fit. How did the person make the ball fit again? What is happening in terms of the kinetic energy of the molecules in the ball? Click here to watch a metal ball and ring demo.

Slide 10 / 112 Thermal Expansion

The change in volume a material experiences due to temperature changes depends on the type of material and the amount of temperature change.

Click here to watch what happens when things expand at different rates.

Slide 11 / 112

1 All matter consists of molecules that are constantly in motion. True False

Slide 12 / 112

1 All matter consists of molecules that are constantly in motion. True False

[This object is a pull tab]

Answer True

Slide 12 (Answer) / 112

2 Temperature is the measure of the average __________ of a substance's molecules. A mass B speed C spacing D kinetic energy

Slide 13 / 112

2 Temperature is the measure of the average __________ of a substance's molecules. A mass B speed C spacing D kinetic energy

[This object is a pull tab]

Answer

• D. kinetic energy

Slide 13 (Answer) / 112

3 After a thunderstorm, the sun comes out and warms a puddle of water that is on the sidewalk. As the puddle of water gets warmer, its molecules: A speed up B slow down C take up less space D gain kinetic energy

Slide 14 / 112

3 After a thunderstorm, the sun comes out and warms a puddle of water that is on the sidewalk. As the puddle of water gets warmer, its molecules: A speed up B slow down C take up less space D gain kinetic energy

[This object is a pull tab]

Answer

• A. speed up
• D. gain kinetic energy

Slide 14 (Answer) / 112 Measuring Temperature

Determining the kinetic energy associated with a substance's molecules would be difficult. Thermometers are used as a more practical way to measure an object's temperature. A thermometer usually consists of a small amount of liquid, such as mercury or colored alcohol, in a narrow tube.

Slide 15 / 112

Temperature Scales

Three scales of temperature commonly used are: · Fahrenheit: used primarily in the United States · Celsius: 1 degree Celsius= 3.2 degrees Fahrenheit · Kelvin: is based on absolute zero, the lowest temperature something can have.

Slide 16 / 112 Temperature Scales Slide 17 / 112 Slide 18 / 112

Slide 19 / 112 Temperature Conversions

The lowest temperature an object can have is the lowest value on the Kelvin scale 0 K! Example: Water boils at 100 °C. What is the boiling temperature

• f water in Kelvin?

The answer is 373 K. Just add 273 to 100 °C! Click the pot of boiling water for the answer! One Kelvin is equal to one degree on the Celsius scale. To convert from Celsius to Kelvin use the following equation. K= °C +273

Slide 20 / 112

4 The coldest temperature ever recorded was -89.2°C in Antarctica on July 21, 1983. Convert this temperature to °F.

Slide 21 / 112

4 The coldest temperature ever recorded was -89.2°C in Antarctica on July 21, 1983. Convert this temperature to °F.

[This object is a pull tab]

Answer

• 128.6

°F 184 K

Slide 21 (Answer) / 112

5 The coldest temperature ever recorded was -89.2°C in Antarctica on July 21, 1983. Convert this temperature to Kelvin.

Slide 22 / 112

5 The coldest temperature ever recorded was -89.2°C in Antarctica on July 21, 1983. Convert this temperature to Kelvin.

[This object is a pull tab]

Answer

• 128.6

°F 184 K

Slide 22 (Answer) / 112

6 If you measure the temperature of an object, its Kelvin temperature will be larger than its Celsius temperature. A never B always C sometimes D not enough information to determine

Slide 23 / 112

6 If you measure the temperature of an object, its Kelvin temperature will be larger than its Celsius temperature. A never B always C sometimes D not enough information to determine

[This object is a pull tab]

Answer

• B. always

Slide 23 (Answer) / 112

7 The hottest recorded temperature ever recorded was about 329 K in Death Valley, California on July 10,

• 1913. What is this temperature in Celsius?

Slide 24 / 112

7 The hottest recorded temperature ever recorded was about 329 K in Death Valley, California on July 10,

• 1913. What is this temperature in Celsius?

[This object is a pull tab]

Answer 56°C This is a more challenging question in that it requires students to come up with the "equation" for converting Kelvin to Celsius which is the reverse of converting Celsius to

• Kelvin. Have a student show their

work on the board or explain how they got the answer.

Slide 24 (Answer) / 112

8 The temperature in deep space is about 3 Kelvin. What is this temperature in °F ?

Slide 25 / 112

8 The temperature in deep space is about 3 Kelvin. What is this temperature in °F ?

[This object is a pull tab]

Answer about -454 °F

Slide 25 (Answer) / 112

Thermal Energy

Return to Table

• f Contents

Slide 26 / 112 Energy in Matter

Molecules in matter possess Kinetic Energy. Do you remember why molecules have kinetic energy? Which drink is likely to have molecules with MORE kinetic energy? How is kinetic energy related to an object's temperature?

Slide 27 / 112

9 The hotter an object, the faster the molecules in it move. True False

Slide 28 / 112

9 The hotter an object, the faster the molecules in it move. True False

[This object is a pull tab]

Answer TRUE

Slide 28 (Answer) / 112

+ +

• Proton

Neutron Electron

Energy in Matter

Molecules in matter also possess Potential Energy. This energy is based on the attractive and repelling forces that all molecules exert on each other. Recall molecules are made up of individual atoms. Each atom contains a positively charged nucleus and negatively charged electrons outside the nucleus.

Slide 29 / 112

10 Protons and electrons A attract each other B repel each other C other

Proton Electron

Slide 30 / 112

10 Protons and electrons A attract each other B repel each other C other

Proton Electron

[This object is a pull tab]

Answer A

Slide 30 (Answer) / 112

11 Opposite charges attract and like charges A attract each other B repel each other C other

Slide 31 / 112

11 Opposite charges attract and like charges A attract each other B repel each other C other

[This object is a pull tab]

Answer B

Slide 31 (Answer) / 112

Repelling force between electrons and electrons Attractive force between positive and negative charges

Energy in Matter

When atoms and molecules interact, electrons are attracted to protons and repelled by other electrons. Atoms in a molecule are "bonded" together because their positively charged nuclei and negatively charged electrons are attracted to each other.

Slide 32 / 112 Energy in Matter

As the distance between atoms and molecules increases, the forces of attraction and repulsion decrease and the potential energy decreases.

Slide 33 / 112 Energy in Matter

The electrical potential energy is inversely proportional to the distance between molecules in matter. What does this inversely proportional relationship mean? The closer the molecules are together, the more potential energy they possess. The farther apart molecules are, the less potential energy they possess.

Slide 34 / 112

Energy in Matter

Can you rank the amount of stored potential energy each state of matter has from highest to lowest? Think about the spacing between molecules! Solid, liquid, gas

Slide 35 / 112

12 What two types of energy do molecules in matter possess? A Potential Energy B Kinetic Energy C Gravity D Thermal Energy

Slide 36 / 112

12 What two types of energy do molecules in matter possess? A Potential Energy B Kinetic Energy C Gravity D Thermal Energy

[This object is a pull tab]

Answer A & B

Slide 36 (Answer) / 112

13 What type of energy describes the motion of molecules in matter? A Kinetic Energy B Potential Energy

Slide 37 / 112

13 What type of energy describes the motion of molecules in matter? A Kinetic Energy B Potential Energy

[This object is a pull tab]

Answer Kinetic Energy

Slide 37 (Answer) / 112

14 Potential energy found in matter is based on the ___________________ between the molecules in matter. A energy B attraction C repulsion D electrons

Slide 38 / 112

14 Potential energy found in matter is based on the ___________________ between the molecules in matter. A energy B attraction C repulsion D electrons

[This object is a pull tab]

Answer B

Slide 38 (Answer) / 112 Thermal Energy

The TOTAL kinetic and potential energy associated with ALL molecules in a substance is called thermal energy. Potential Energy Kinetic Energy Thermal Energy Thermal energy and temperature are NOT the same because temperature only considers the average kinetic energy of molecules. TOTAL molecular energy

Slide 39 / 112 Thermal Energy versus Temperature

Both containers of water below are measured to have the same

• temperature. However, one container of water has MORE thermal

energy. It has more water molecules! Which has more thermal energy. Why? Click on the bucket for the answer.

Slide 40 / 112

Energy Transfer

Return to Table

• f Contents

Slide 41 / 112

Heat flows from the mug to the hand. Thermal energy transfers from the tongue to the ice cream.

Heat and Energy Transfer

Heat is the transfer of thermal energy from a higher temperature

• bject or location to a lower temperature object or location.

Why does the ice cream feel cold on the tongue? Click for the answer Why does the mug of hot cocoa feel warm? Click for the answer.

Slide 42 / 112 Heat

The amount of heat flow depends on the temperature difference between objects or locations. Bigger temperature difference

more HEAT

Lower temperature difference

less HEAT

No temperature difference no heat (thermal equilibrium)

Slide 43 / 112

15 Thermal energy and temperature describe the same thing. True False

Slide 44 / 112

15 Thermal energy and temperature describe the same thing. True False

[This object is a pull tab]

Answer False

Slide 44 (Answer) / 112

16 Heat is the transfer of thermal energy when there is temperature difference between objects or locations. True False

Slide 45 / 112

16 Heat is the transfer of thermal energy when there is temperature difference between objects or locations. True False

[This object is a pull tab]

Answer True

Slide 45 (Answer) / 112

17 Thermal energy moves from hotter objects or locations to colder objects or locations. True False

Slide 46 / 112

17 Thermal energy moves from hotter objects or locations to colder objects or locations. True False

[This object is a pull tab]

Answer True

Slide 46 (Answer) / 112

18 Which object will have the greatest heat exchange with a room that is at 20 degrees Celsius? A ice cold water (at 6 degrees celsius) B luke warm water C room temperature water D boiling water (at 100 degrees celsius)

Slide 47 / 112

18 Which object will have the greatest heat exchange with a room that is at 20 degrees Celsius? A ice cold water (at 6 degrees celsius) B luke warm water C room temperature water D boiling water (at 100 degrees celsius)

[This object is a pull tab]

Answer D boiling water because of the biggest difference in temperature with the environment.

Slide 47 (Answer) / 112 Methods of Energy Transfer

Heat transfer can occur by: · direct contact - Conduction · electromagnetic waves - Radiation · molecular movement - Convection

Slide 48 / 112

Conduction

Heat transfer through direct contact is known as conduction. This causes the molecules in the ice to move faster and the molecules in the finger to move slower. How does this relate to the temperature change the ice experiences? The energy of faster moving molecules in the warmer finger transfers to the slower moving molecules of the colder ice by bumping into them.

Slide 49 / 112 Conduction

Click here to watch conduction in action

Look at this Navy

• cook. Why is he

using pot holders to carry the turkey?

Slide 50 / 112 Conduction

Conduction occurs most easily in solids because their molecules are closer together. Let's come up with some other examples of conduction below.

Slide 51 / 112

19 Heat transfer by conduction involves direct physical _____________. A transfer B movement C contact D fire

Slide 52 / 112

19 Heat transfer by conduction involves direct physical _____________. A transfer B movement C contact D fire

[This object is a pull tab]

Answer C

Slide 52 (Answer) / 112

20 Conduction occurs most easily in ____________ because molecules are closer together. A gases B liquids C solids D all of the above

Slide 53 / 112

20 Conduction occurs most easily in ____________ because molecules are closer together. A gases B liquids C solids D all of the above

[This object is a pull tab]

Answer

• C. solids

Slide 53 (Answer) / 112

21 Feeling the warmth of a campfire on your skin is an example of conduction. True False

Slide 54 / 112

21 Feeling the warmth of a campfire on your skin is an example of conduction. True False

[This object is a pull tab]

Answer False, there is no direct physical contact.

Slide 54 (Answer) / 112

Radiation

Do you have to touch the sun to feel its warmth? Heat transfer by electromagnetic waves through empty space or matter is known as radiation. Of course not! The sun radiates energy in the form of electromagnetic waves. Molecules in your skin move faster after you absorb this energy causing your temperature to rise. Click for the answer

Slide 55 / 112 Radiation

Discuss why you think a person feels warmer in a room full of people than in a room by themselves. All objects radiate electromagnetic wave energy. The hotter an object, the more energy it radiates.

Slide 56 / 112 Radiation

Heat transfer through radiation does not involve the movement of matter. Let's come up with some other examples of radiation below.

Slide 57 / 112

22 Heat transfer by ______________ is called radiation. A movement of matter B sweating C molecular motion D electromagnetic waves

Slide 58 / 112

22 Heat transfer by ______________ is called radiation. A movement of matter B sweating C molecular motion D electromagnetic waves

[This object is a pull tab]

Answer D electromagnetic waves

Slide 58 (Answer) / 112

23 Radiation can not occur through empty space that has no matter. True False

Slide 59 / 112

23 Radiation can not occur through empty space that has no matter. True False

[This object is a pull tab]

Answer False

Slide 59 (Answer) / 112

24 Which of the following radiate energy in the form of electromagnetic waves? A bowl of soup B the sun C a lake D humans

Slide 60 / 112

24 Which of the following radiate energy in the form of electromagnetic waves? A bowl of soup B the sun C a lake D humans

[This object is a pull tab]

Answer All answers are correct

Slide 60 (Answer) / 112

Convection

Heat transfer from one location to another by the movement

• f liquids or gases is known as convection.

Go through the next few slides to see an example of convection in a liquid.

Slide 61 / 112 Convection

The burner conducts heat to the bottom of the pot.

Slide 62 / 112 Convection

As the water heats up, its density decreases and it begins to rise to the top.

Slide 63 / 112

Convection

The displaced cooler water heats up at the bottom of the pot and the cycle continues creating a convection current. Simultaneously, cooler and denser water at the top is displaced downward.

Slide 64 / 112 Convection

Natural convection also occurs in gases like the atmosphere. A sea breeze is an example

• f convection.

Slide 65 / 112 Convection

Can you come up with any other examples of convection? Make a list with a partner.

Slide 66 / 112

25 Convection occurs in__________. A solids B liquids C gases D all of the above

Slide 67 / 112

25 Convection occurs in__________. A solids B liquids C gases D all of the above

[This object is a pull tab]

Answer

• B. liquids
• C. gases

Slide 67 (Answer) / 112

26 A heater near the floor is turned on during the winter months to heat the room. Convection will occur. True False

Slide 68 / 112

26 A heater near the floor is turned on during the winter months to heat the room. Convection will occur. True False

[This object is a pull tab]

Answer True

Slide 68 (Answer) / 112 Conductors versus Insulators

Materials that transfer heat easily through conduction are called conductors. Insulators are materials that transfer heat poorly.

Insulator Conductor

Why would the handle

• f a frying pan be

made of a different material than the body?

Slide 69 / 112 Conductors versus Insulators

Materials that are good conductors have atoms with "loose" electrons that can bump into other atoms and easily transfer thermal energy. Metals like the base of this pan are good conductors. Hot to the touch Cold to the touch Why is a metal frying pan cold to the touch when not in use, but hot when over a fire? Good conductors are usually poor insulators.

Slide 70 / 112

Conductors

Materials that are good conductors have atoms with "loose" electrons that can bump into other atoms and easily transfer thermal energy. silver aluminum copper water

Slide 71 / 112 Insulators

Insulators are usually porous materials with air spaces that act to reduce the transfer of heat. Good insulators are usually poor conductors. glass plastic wood air

Slide 72 / 112 Conductors versus Insulators

A pizza baker's hands feel warm when in close proximity to the

• ven but will only burn if he accidentally touches the oven.

Air in and around the oven is a poor conductor whereas the metal

• ven is an excellent conductor of
• heat. The hotter oven will therefore

transfer thermal energy to his cooler hand if he touches it. Why is this the case? Click for the explanation.

Slide 73 / 112

27 Conductors do not transfer heat easily while insulators do. True False

Slide 74 / 112

27 Conductors do not transfer heat easily while insulators do. True False

[This object is a pull tab]

Answer False

Slide 74 (Answer) / 112

28 Louisa wants to be able to hold a cup of hot cocoa while she waits for the bus. Which cup should she choose? A styrofoam cup B aluminum cup C glass cup D plastic cup

Slide 75 / 112

28 Louisa wants to be able to hold a cup of hot cocoa while she waits for the bus. Which cup should she choose? A styrofoam cup B aluminum cup C glass cup D plastic cup

[This object is a pull tab]

Answer All answers except aluminum which is a metal are acceptable. The hot cocoa will heat the cup and she wants a cup that will not transfer the cup's thermal energy easily to her hand.

Slide 75 (Answer) / 112

Specific Heat

Return to Table

• f Contents

Slide 76 / 112 Specific Heat

You reach for a slice of pizza fresh from the hot oven. You take a bite and the crust is nice and warm but when the sauce reaches your tongue it burns! If the sauce and crust were at the same temperature, why do you think the sauce burned your tongue but the crust did not?

Slide 77 / 112

The sauce required more thermal energy to reach the same temperature as the crust because it had a higher specific heat capacity than the crust.

Specific Heat

The sauce transferred more thermal energy to your tongue raising your tongue's temperature. But why did the sauce have more thermal energy than the crust? Click HERE for the answer.

Slide 78 / 112 Specific Heat

Specific heat describes the amount of energy in Joules (J) needed to raise the temperature of 1 kg of a substance by 1°C.

table: electron9.phys.utk.edu

Different substances have different specific heat capacities. What do those values tell you about the substance?

Slide 79 / 112 Specific Heat

Differences in specific heat require different amounts of energy for the same change in temperature.

1kg

It takes about 800 Joules of energy to raise the temperature of 1 kg of rock by 1°C.

Slide 80 / 112

1kg

Specific Heat

It takes about 1,700 Joules of energy to raise the temperature of 1 kg

• f wood by 1°C.

Which has the higher specific heat capacity, the rock or the wood?

Slide 81 / 112

lowest specific heat specific heat is in between highest specific heat temperature will be in between highest temperature lowest temperature lowest specific heat specific heat is in between highest specific heat

Specific Heat

What happens if the same amount of thermal energy is transferred to substances of the same mass but different specific heats? For example, if equal masses of water, sand and air each recieve 1000 Joules

• f energy how do their

temperatures compare? Click the picture for the answer.

Slide 82 / 112

29 Specific heat describes the energy needed to raise the temperature of 1kg of a substance by 1°C. True False

Slide 83 / 112

29 Specific heat describes the energy needed to raise the temperature of 1kg of a substance by 1°C. True False

[This object is a pull tab]

Answer True

Slide 83 (Answer) / 112

30 Which substance requires the least amount of energy to change its temperature by the same amount? A 1 kg of ice B 1 kg of lead C 1 kg of water D 1 kg of copper

table: electron9.phys.utk.edu

Slide 84 / 112

30 Which substance requires the least amount of energy to change its temperature by the same amount? A 1 kg of ice B 1 kg of lead C 1 kg of water D 1 kg of copper

table: electron9.phys.utk.edu

[This object is a pull tab]

Answer B 1 kg of lead It has the lowest specific heat.

Slide 84 (Answer) / 112

31 Exactly 200 Joules of thermal energy are transferred to the following substances. Which undergoes the least amount of temperature change? A 1 kg of water B 1 kg of copper C 1 kg of iron D 1 kg of aluminum

table: electron9.phys.utk.edu

Slide 85 / 112

31 Exactly 200 Joules of thermal energy are transferred to the following substances. Which undergoes the least amount of temperature change? A 1 kg of water B 1 kg of copper C 1 kg of iron D 1 kg of aluminum

table: electron9.phys.utk.edu

[This object is a pull tab]

Answer B 1kg of water Since it has the highest heat capacity, it requires a lot more energy to change its temperature by the same amount.

Slide 85 (Answer) / 112 Specific Heat

Identical substances with the same mass and the same specific heat will undergo different temperature changes if they recieve different amounts of thermal energy. Use a red marker tool to illustrate on the thermometers the differences in water temperature between the two flasks of water.

Slide 86 / 112

Specific Heat

Identical substances with different masses and the same specific heat will undergo different temperature changes if they recieve the same amount of thermal energy. Use a red marker tool to illustrate on the thermometers the differences in temperature between the two rocks.

Slide 87 / 112

32 Suppose two identical rocks of the same mass and same specific heat are heated differently. How could you determine which rock received more thermal energy?

Students type their answers here

Slide 88 / 112

32 Suppose two identical rocks of the same mass and same specific heat are heated differently. How could you determine which rock received more thermal energy?

Students type their answers here

[This object is a pull tab]

Answer Measure each rock's temperature. The rock with the higher temperature had more thermal energy transferred to it.

Slide 88 (Answer) / 112

33 Suppose two identical rocks of different masses are

• heated. After they each receive 200 Joules of thermal
• energy. Rock "A" has a hotter temperature than rock

"B". Which rock is more massive? A B Rock Rock

Slide 89 / 112

33 Suppose two identical rocks of different masses are

• heated. After they each receive 200 Joules of thermal
• energy. Rock "A" has a hotter temperature than rock

"B". Which rock is more massive? A B Rock Rock

[This object is a pull tab]

Answer Rock B is more massive.

Slide 89 (Answer) / 112 Temperature Changes

To summarize, the temperature changes a substance undergoes: Are inversely proportional to the specific heat of the substance

higher specific heat smaller temperature change

lower specific heat

greater temperature change Slide 90 / 112

Are directly proportional to the amount of energy transferred to the substance.

Temperature Changes More energy greater temperature change less energy smaller temperature change Slide 91 / 112

Are inversely proportional to the mass of the substance

1kg 2kg

Temperature Changes more mass smaller temperature change

less mass

greater temperature change Slide 92 / 112

34 What three quantities does the temperature change

• f an object depend on?

A the object's density B the amount of energy transferred to it C the object's mass D the object's specific heat

Slide 93 / 112

34 What three quantities does the temperature change

• f an object depend on?

A the object's density B the amount of energy transferred to it C the object's mass D the object's specific heat

[This object is a pull tab]

Answer All except the object's density.

Slide 93 (Answer) / 112

35 100 Joules of thermal energy are added to the following objects. Which undergoes the greatest temperature change? A 1 kg of aluminum B 3 kg of aluminum C 1 kg of water D 3 kg of water

table: electron9.phys.utk.edu

Slide 94 / 112

35 100 Joules of thermal energy are added to the following objects. Which undergoes the greatest temperature change? A 1 kg of aluminum B 3 kg of aluminum C 1 kg of water D 3 kg of water

table: electron9.phys.utk.edu

[This object is a pull tab]

Answer A

Slide 94 (Answer) / 112

Finding Temperature Change

TE ∆T = mc Thermal energy (Joules, J) mass (kilograms, kg) specific heat capacity (Joules/°C∙kg) change in temperature (°C) Consistent with these relationships is the following equation for change in temperature.

Slide 95 / 112 Finding Temperature Change

Try using the equation for the following. How much thermal energy must be added to 130 kg of bath water to change its temperature from 33°C to 37°C? The specific heat

• f water is 4186 J/°C∙kg.

Slide 96 / 112 Finding Temperature Change

Try using the equation for the following. How much thermal energy must be added to 130 kg of bath water to change its temperature from 33°C to 37°C? The specific heat

• f water is 4186 J/°C∙kg.

[This object is a pull tab]

Answer TE= (m × c) × ∆T = (130kg × 4186 J/°C∙kg) × 4°C Don't forget, this is the change in

• temperature. (37°C-33°C= 4°C)

Slide 96 (Answer) / 112

36 A 0.03kg silver spoon with a specific heat of about 300 J/°C∙kg is placed into a cup of soup. The soup transfers 90 J of thermal energy to the spoon. What is the change in the spoon's temperature in °C?

Slide 97 / 112

36 A 0.03kg silver spoon with a specific heat of about 300 J/°C∙kg is placed into a cup of soup. The soup transfers 90 J of thermal energy to the spoon. What is the change in the spoon's temperature in °C?

[This object is a pull tab]

Answer 10°C

Slide 97 (Answer) / 112

37 You want to cool 0.35 kg of water from room temp 20°C to 5°C. How much thermal energy must be removed from the water? Water has a specific heat of 4186 J/°C∙kg.

Slide 98 / 112

37 You want to cool 0.35 kg of water from room temp 20°C to 5°C. How much thermal energy must be removed from the water? Water has a specific heat of 4186 J/°C∙kg.

[This object is a pull tab]

Answer 21, 977 J of thermal energy must be removed. *Teacher Note: Use of the equation remains the same despite the fact that we are removing thermal

• energy. Only the terminology has

changed: "added" is now "removed" and the temperature of course is dropping instead of getting larger.

Slide 98 (Answer) / 112

38 A 0.20 kg aluminum baking pan is placed in an oven and absorbs 20,000J of thermal energy. If the baking pan had a starting temperature of 20°C, what is its temperature after being heated? The specific heat of aluminum is 900J/°C∙kg.

Slide 99 / 112

38 A 0.20 kg aluminum baking pan is placed in an oven and absorbs 20,000J of thermal energy. If the baking pan had a starting temperature of 20°C, what is its temperature after being heated? The specific heat of aluminum is 900J/°C∙kg.

[This object is a pull tab]

Answer 131.1°C If you use the equation to solve for ∆T, you get about 111.1°C. Since the pan started at 20°C then its final temperature will be 20°C plus 111.1 °C.

Slide 99 (Answer) / 112

Thermodynamics and Energy Conservation

Return to Table

• f Contents

Slide 100 / 112 Slide 101 / 112 Slide 102 / 112

1st Law of Thermodynamics

The 1st law of thermodynamics is the law of conservation of energy. Energy can not be created or destroyed, only converted from one form to another. Work is done on the stick giving it kinetic

• energy. This kinetic

energy is converted into heat energy.

Slide 103 / 112 2nd Law of Thermodynamics

The 2nd law of thermodynamics states that heat normally flows from high temperature to low temperature. Heat flow is from the warm coffee to the cooler environment. Once the environment around the cup is warmer, the faster moving air molecules can not be forced to reheat the coffee. This is because all systems have a tendency to increase their disorder, or entropy.

Slide 104 / 112 Heat Engine

First drawing air and fuel vapor in. Next, the piston moves up and compresses the air-fuel mix. Fuel combusts and the air-fuel mix expands to pushes down on the piston, and the exhaust is driven out. Heat engines convert thermal energy into mechanical energy. Internal combustion engines in cars convert heat to mechanical energy through the following four-step process.

Slide 105 / 112

39 The study of the relationship between heat and _____________ is called thermodynamics. A thermal energy B friction C work D conductors

Slide 106 / 112

39 The study of the relationship between heat and _____________ is called thermodynamics. A thermal energy B friction C work D conductors

[This object is a pull tab]

Answer work

Slide 106 (Answer) / 112

40 When work is done an object, there is a transfer of energy. True False

Slide 107 / 112

40 When work is done an object, there is a transfer of energy. True False

[This object is a pull tab]

Answer true

Slide 107 (Answer) / 112

41 The 1st law of thermodynamics is basically a restatement of the law of conservation of _____________. A heat B energy C convection D forces

Slide 108 / 112

41 The 1st law of thermodynamics is basically a restatement of the law of conservation of _____________. A heat B energy C convection D forces

[This object is a pull tab]

Answer B - energy

Slide 108 (Answer) / 112

42 Which of the following are examples of the 1st law of thermodynamics? (pick more than one) A you rub your hands together and they get warmer B a chandelier hangs suspended from the ceiling C the brakes cause a car's tires to skid on the road D a person gets tired holding a tray above their head

Slide 109 / 112

42 Which of the following are examples of the 1st law of thermodynamics? (pick more than one) A you rub your hands together and they get warmer B a chandelier hangs suspended from the ceiling C the brakes cause a car's tires to skid on the road D a person gets tired holding a tray above their head

[This object is a pull tab]

Answer A and C

Slide 109 (Answer) / 112

43 The 2nd law of thermodynamics states that heat flows from colder objects to hotter objects. True False

Slide 110 / 112

43 The 2nd law of thermodynamics states that heat flows from colder objects to hotter objects. True False

[This object is a pull tab]

Answer False

Slide 110 (Answer) / 112

44 Entropy is the measure of order a system has. The more entropy a system has the more ordered it is. True False

Slide 111 / 112

44 Entropy is the measure of order a system has. The more entropy a system has the more ordered it is. True False

[This object is a pull tab]

Answer False

Slide 111 (Answer) / 112

45 Heat engines convert thermal energy (or heat) into _____________ energy. A thermal B mechanical C potential D convection

Slide 112 / 112

45 Heat engines convert thermal energy (or heat) into _____________ energy. A thermal B mechanical C potential D convection

[This object is a pull tab]

Answer B - mechanical

Slide 112 (Answer) / 112