PAGE 72 Nov. 13, 2012

Focus: Heat TransferObjective: 6.P.3.1-I will be able to

illustrate the transfer of heat energy from warmer objects to cooler ones using examples of conduction, radiation and convection

HW: Graph results of lab, conclusionWarm-Up: Practice* At your tables, answer in complete

sentences, Questions 1- 3

LAB

The Nature of Heat

Heat moves in only one direction:

HIGHENERGY

LOWENERGY

HOT COLD

The water is 25°C and the magnet is 55°C.a. How will energy move?

 

b. How will the temperatures of the water and magnet change?

c. When will energy stop moving and how will you know?

Energy will move from the Hot magnet to the Cold water.

The magnet will get colder and the water will get hotter.

Energy will stop moving when the magnet and water have reached equilibrium. You will know they are at equilibrium when they are the same temperature.

25 C

55 C

You make a lasagna to take to a dinner. You put the hot lasagna in a cold cooler

a. How will energy move?

 

b. How will the temperatures of the lasagna and cooler change?

c. When will energy stop moving and how will you know?

Energy will move from the Hot lasagna to the Cold cooler.

The lasagna will get colder and the cooler will got hotter.

Energy will stop moving when the lasagna and cooler have reached equilibrium. You will know they are at equilibrium when they are the same temperature.

If you put a hot lasagna into a cooler, would “cold” transfer from the cooler to the lasagna, or would “hot” transfer from

the lasagna to the cooler?

Hmmmm….

Why does the lasagna get cold in the cooler?

Because the HOT lasagna

gives its energy to the

COLD cooler (energy

moves from hot-> cold),

making the lasagna cool down until both reach EQUILIBRIUM!

Here is how it works:• Heat Energy is what makes the lasagna

hot.• Since the inside of cooler has a lower

temperature than the lasagna, heat energy travels from the lasagna to the cooler.

HIGHENERGY

LOWENERGY

HOT COLD

3. In which direction is energy flowing?

 

4. When will energy stop flowing?

 

5. What will happen to the temperatures of the water in Beaker A and Beaker B?

 

6. Based on the picture above, approximately what temperature will equilibrium be?

93°C 42°C

Metal Bar

From Beaker A (HOT) to the Metal Bar to Beaker B (COLD)

When equilibrium is reached (all 3 are the same temp.)

Beaker A will cool down and Beaker B will warm up.

B. Between 42C and 93C.

7. How will you know when equilibrium is reached?

 

8. After 40 minutes, equilibrium is established. The temperature of Beaker A is 60°C. What must be the temperature of Beaker B?

 

9. Which best describes what is happening to Beaker A?

93°C 42°C

Metal Bar

When Beaker A, the Metal Bar, and Beaker B are the same temperature.

Beaker B must be the same temperature as Beaker A: 60°C

A. Beaker A releases energy and becomes colder

Now that we know which way heat energy travels (from hot to cold),

how does it actually travel?

There are three types of heat transfer:

• CONDUCTION• CONVECTION• RADIATION

HEAT TRANSFER

CONDUCTION CONVECTION RADIATION

• The transfer of heat by direct contact between objects (touching).

• cooking on a stove • hot sand touching your feet • Burning your mouth on a

bite of pizza

http://viewpure.com/IYfEj3JSMbA

• Heat transferred by the movement of a liquid or gas from warmer areas to cooler areas.

Examples: Wind, Boiling Water, Steam

Convection also produces CURRENTS.– Remember convection

currentshttp://viewpure.com/ON2Y3FEk_UI

Radiation – The direct transfer of electromagnetic waves. Cannot see it, but can feel heat

How does heat energy get from the Sun to the Earth?

There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection.

?RADIATION

• Transfer of energy between two objects that are NOT touching.

• EXAMPLES: The sun’s rays causing a sunburn.

• heat from toaster • heat from a light bulb • heat from a fire • MICROWAVE! http://viewpure.com/2JZciWtK6vc

Q.) When you put a teapot on the stove to boil water, which of the three kinds of heat transfer can be observed?

Q.) When you put a teapot on the stove to boil water, which of the three kinds of heat transfer can be observed?

A.) Actually, all three!

Conduction, Convection, or Radiation

hot water rises and cold water sinks

a spoon in a cup of hot soup becomes warmer

heat from a light bulb

Conduction, Convection, or Radiation

microwave oven

frying chicken strips

boiling potatoes in water

Think, Write, Pair, Share

Mac and Cheese1. I microwaved some macaroni and cheese.

What type of heat transfer is this?

2. When I bite into the macaroni and cheese, it burns my tongue. What type of heat transfer is this?

 3. There is steam rising from the macaroni and

cheese, which warms my face. What type of heat transfer is this?

The energy transfer is RADIATION from the microwave.

The energy transfer is CONDUCTION.

The energy transfer is CONVECTION.

4. Ms. McCallister is making some soup. She puts a spoon into the boiling soup and the spoon gets hot. Then, she touches the spoon , and it feels hot on her hand. Describe the sequence of thermal energy transfers in this situation (Hint: there are 2 transfers).The energy transfer is from the boiling soup to the spoon is CONVECTION. The energy transfer is from the spoon to the hand is CONDUCTION.

5. Ms. Lappin’s car has been sitting in the sun all day long. The sun is heating the car, and the hot air inside the car is warming up the metal seat belt. When she grabs the seat belt, it burns her hand. Describe the 3 types of thermal energy transfers that have occurred. The energy transfer from the SUN to the CAR is RADIATION. The energy transfer from the AIR IN THE CAR to the SEAT BELT is CONVECTION.The energy transfer from the SEAT BELT to the HAND is CONDUCTION.

Video Clip on HEAT transfer

http://viewpure.com/wr8Z4SCETPs

Independent Practice

Now, answer the three questions on the back of your note sheet.

Homework Questions

Write answers on page 114:

1.If you put a cup of hot chocolate into a refrigerator, would “cold” transfer from the fridge to the hot chocolate , or would “hot” transfer from the hot chocolate to the fridge? Explain.

2.During the summer as you walk along the hot sand you get a sun burn. What are the two types of heat transfer?

STOP HERE

2.3

SECTIONOUTLINESECTIONOUTLINE

The transfer of energy as heat can be controlled.

conductor

conduction

insulator

convection

radiation

• Different materials are used to control the transfer of energy.

• Energy can be transferred by conduction, convection, and radiation.

Types of Energy Transfer

• Continues until object temperatures are equal

Conduction

• Energy transferred by direct contact

• Energy flows directly from warmer object to cooler object

• Can occur within one object

• Cycle occurs while temperature differences exist

Convection

• Occurs in gases and liquids

• Movement of large number of particles in same direction

• Occurs due to difference in density

• Can transfer energy through empty space

Radiation

• Energy transferred by electromagnetic waves such as light, microwaves, and infrared radiation

• All objects radiate energy

Radiation

Key Point: For radiation to be felt as heat it must first be absorbed by a material.

Example: Why do blue jeans feel hotter in the sun than a yellow shirt, even though they are both exposed to the same amount of sunlight?

– The blue jean fabric absorbs more radiant energy from the sun than the yellow shirt because of its dark color.

Conduction

Example: A metal spoon in a pot of water being heated on an electric stove.

a. First, the electrical energy is converted to thermal energy by the stove.

b. The rapidly vibrating particles of the hot electric coil collide with the particles of the cool pot.

c. Heat energy is transferred, causing the particles in the pot to vibrate faster.

Conduction

d. The rapidly vibrating particles of the pot now collide with the particles of the water at the bottom of the pot.

e. The water particles absorb energy and vibrate and flow more rapidly and its temperature increases.

f. Now, the energetic (hot) particles of water collide with the particles of the submerged end of the spoon.

g. As the particles of the spoon absorb energy and vibrate more rapidly. The temperature of the spoon increases.

Conduction

h. As the particles at this end of the spoon absorb energy and vibrate faster they collide with other particles in the spoon. As they collide, energy is transferred to the other particles (similar to momentum) and they begin to vibrate more rapidly.

i. This process of conduction is repeated all along the metal spoon until the entire metal spoon becomes hot.

Convection

Convection: the transfer of thermal energy (heat) through the bulk movement of matter.

– Convection occurs in FLUIDS (liquids and gases).

– Convection produces CURRENTS in both gases and liquids.

– Thermal Energy heat is carried by the particles as they move from one location to another.

ConvectionExample: Heating water:

a. When the water at the bottom of the pot (nearest the burner) is heated, the particles absorb energy by conduction as they touch the hot pot.

b. The water particles vibrate more rapidly.c. The particles also move farther apart and

the hot water becomes less dense than the surrounding cool water.

d. This causes the heated (hot) water to rise.