Energy: Conservation & Transfer: Conductors and Insulators

1. How is thermal energy transferred?2. Why do materials expand and

contract?3. What materials are good conductors?4. What materials are good insulators?Key Vocabularythermal expansion, conduction, conductors, insulators, ,heat, kinetic energy, temperature,  volume (matter)

Lesson Essential Questions

When you apply a flame to the lid of a sealed food jar, the heat of the flame will loosen the lid's molecules, causing the lid to expand and making it easier to open. When the lid cools down, however, its molecules will contract, causing the lid to shrink back to its normal size.

In this lesson, you will learn: How an object's temperature causes it to

expand or contract. What is a good thermal/electrical conductor

and what is a good thermal/electrical insulator.

Thermal Expansion and Contraction

Heat - the transfer of thermal energy◦What happens to your hot soup if you take too long to eat it?

◦It loses heat. ◦Heat is what happens when thermal energy is gained or lost.

◦To warm your soup up, you can add more energy using a microwave or stove.

Kinetic energy - the energy an object has because of its motion.

Vocabulary Review

Temperature -a measure of the average kinetic energy (energy of motion) of the atoms in a system,

Temperature is used to express thermal energy in degrees◦Temperature is the measure of how hot or cold something is.

◦ In physics, temperature is directly proportional to the amount of kinetic energy of the molecules of a substance. If kinetic energy increases – temperature

increases! If kinetic energy decreases – temperature

decreases!◦Temperature is measured in Kelvin, degrees Celsius or degrees Fahrenheit.

Thermal energy - energy in the form of heat.◦ Heat is the flow of energy from a hot object to

a cooler one.

◦ When you feel that heat, in a cup of hot chocolate or the warmth of sunlight, you are actually feeling thermal energy.

◦ Thermal energy is the movement of molecules that make up the object. An object has more thermal energy when it is warm than when it is cool.

◦ Heat is the transfer of thermal energy from one object to another.

Heat is energy in motion. Temperature is a measure of that energy.

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Heat and Temperature are NOT the same!

Many things give off heat. All heat is energy.

That’s hot!

Sun fire electricity

Pretend you are at a campfire. You are roasting a hot dog on a metal wire coat hanger.

Slowly the end of the hanger warms up, as it takes in the heat from the fire.

Campfire!

If you leave the hanger in the fire for a long time, the whole hanger will become to hot to touch!

Ouch!

•Why does this happen?

This happens even though the handle end was never placed into the flames.

Heat moves from the flames to the metal handle.

From there it moves to all the molecules in the hanger by conduction until it reached your fingers.

Here’s the reason….

Heat can move from one object to another, or from one molecule to another through the process of conduction. (RECALL LESSON #1)

Heat on the move!

As one molecule is heated it begins to move quickly.

When it does it passes some of its heat energy to other molecules around it.

When this happens, all the molecules of an object move heat from one to another, until they are all hot.

Hot All Over!

Heat can be transferred from one object to another through conduction, convection, or radiation.

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Heat Transfer

HEAT - Always flows from regions of HIGHER temperature to regions of LOWER temperature. (RECALL – Lesson 1)

HEAT - Always caused by a difference of temperature.

HEAT - is the exciting of molecules.

Basics of HEAT FLOW

Heat is conducted by the direct transfer of kinetic energy (energy of motion) from one object or substance to another.

Molecules transfer kinetic energy as they collide.

Objects or substances need to be in direct contact in order for conduction to occur. 

How is heat conducted through solids, liquids, and gases?

  REVIEW!!!!!!!! Heat is the transfer of thermal energy

from a warmer object to a cooler object.

Temperature is a measure of the average kinetic energy of the particles that make up an object.

Heat moves through objects.

This is called conduction!

Remember….

Some materials (objects) get warmer faster than others.

Metal is a good conductor because it takes heat in quickly.

Copper becomes hot quickly, so it is a conductor.

A good conductor transfers heat quickly

What things get hot fast?

Copper pots

What are Conductors? Conductors are materials that allow

heat to move easily through them.  

Do you like toast? Did you ever look inside a toaster while it’s toasting bread? When you push down the lever to turn on the toaster, the metal heating element inside starts to glow orange or red almost instantly. You can see the glowing heating element inside this yellow toaster.

The glowing metal shows that the heating element has become very hot. It gets hot so quickly because metals are good conductors of thermal energy.

Good ConductorsMany metals, like silver, copper, gold and aluminum, are good thermal conductors. 

Conductors of Heat!

Glass?????Glass is a poor conductor of heat, especially in comparison to other materials, such as metal. Glass does conduct some heat, but does so more slowly than other materials.

Other things like wood, plastics, and cotton are NOT good conductors of heat energy.

These are called insulators.

You’re no good!

Insulators are materials that do not allow heat to move easily through them.

What are Insulators?

The trapped air acts as an insulator!!!

Feathers act as an insulator!

Wood Paper Cotton Wool Plastic Feathers Dry air Fiberglass

Good Thermal Insulators

Air, like other gases, is a poor conductor of thermal energy.

The particles of gases are relatively far apart, so they don’t bump into each other or into other things as often as the more closely spaced particles of liquids or solids.

Therefore, particles of gases have fewer opportunities to transfer thermal energy.

Remember - Materials that are poor thermal conductors are called thermal insulators.

.

Thermal Insulator - AIR???????

What do thermal Insulators help do?

What is an electrical conductor? An electrical conductor is something which

allows electricity to flow through easily.

An example of a conductor is:◦ Scissors◦ Paper clip◦ Aluminum foil◦ Iron◦ Steel◦ Copper

What is an electrical Insulator? An electrical insulator does not allow

electricity to flow through it easily.

Examples of insulators are:◦ Cotton◦ Paper◦ Plastic◦ Glass◦ Rubber

These are pictures of conductors and Insulators

Conductors Insulators

DEMONSTRATION

Draw the following picture in your guided notes.

TAKE A LOOK!

Set up the equipment as shown and tape the wires to the battery.

•Does anything happen? •Does the banana allow electricity to flow through the circuit and light the bulb?•Is it a conductor or an insulator? Why or why not?

Inquiring Minds Want to Know! Conductor or Insulator? That is the question!

Now lets look at the following materials!

1. Guess whether each item is a conductor or an insulator with a “X”

2. As we test each item, record whether it was a conductor or and insulator with a

Item Conductor Insulator Did the bulb light?

Spoon

Paper clip

pencil

Rubber band

eraser

Foil

Nail

coin

When heat is added to matter, the heat makes the matter’s particles move faster…..

the particles spread farther a p a r t and the matter begins to

expand, or increase in volume.

Why do materials expand and contract?

Removing heat causes the opposite process, and the matter contracts.

When an object cools it contracts.

Different types of matter expand differently

SOLIDS - As a solid is heated the molecules vibrate more violently and the solid expands in all directions.

Different materials expand by different amounts for the same rise in temperature.

GASES - Under equal pressures, all gases expand at the same rate.

LIQUIDS - Unlike gases, liquids expand at different rates, depending on their composition. ◦ Liquids also expand by different amounts at different

temperatures

What causes the liquid in a thermometer to rise and fall?

The way a thermometer works is an example of heating and cooling a liquid. ◦ (THERMAL EXPANSION AND CONTRACTION)

When heated, the molecules of the liquid in the thermometer move faster, causing them to get a little further apart. This results in movement up the thermometer.

When cooled, the molecules of the liquid in the thermometer move slower, causing them to get a little closer together. This results in movement down the thermometer.

Thermometers!

Solids vary greatly in their response to heat.

Expansion joints are placed in roads, bridges, railroad tracks and sidewalks to help with expansion and contraction in these solids!

 

On a hot day if a bridge, sidewalk, railroad track or road is NOT engineered to withstand thermal expansion and contraction…it could buckle!

Although most substances expand when heated, not all expand at the same rate.

Aluminum, for example, expands twice as much as iron when both are heated the same amount.

Rubber and water are two common substances that differ from most others in their response to heat.

Rubber contracts when heated instead of expanding! Water also expands when it freezes!!!!! The fact that water expands upon freezing causes icebergs

to float.  Water expands when its temperature rises above

(39° F.)

Reference https://www.physicsforums.com/threads/warm-water-expands.117443/

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An object’s temperature increases as a result of the kinetic energy of its molecules increasing….. As an object’s molecules move faster and over greater distances, they take up more space, and the object expands.

An object cools as a result of the kinetic energy of its molecules decreasing. …..As an object’s molecules move slower and over shorter distances, they take up less space, and the object contracts.

Different materials expand and contract at different rates as heat energy is added or removed.

 

REVIEW - Why do materials expand and contract?

Insulator- does not allow heat/electricity to travel through it easily.

Conductor- does allow heat/electricty to travel through it easily.

REVIEW QUIZ/GAME http://www.ck12.org/book/CK-12-Physi

cal-Science-Concepts/section/5.17/ CLICK ON PRACTICE TAB –

COMPLETE QUIZ/GAME

Review – Insulators & Conductors