WELCOME BACK!

Agenda:

1. #throwbackthursday: Question of the Day #28 & 29

2. Energy Vocabulary Quiz

3. Heat & Thermal Energy Notes

Homework: Energy Unit Quiz Review

Thursday, January 29, 2015Objective: Thermal Energy; I will discuss thermal energy and compare the different ways to transfer heat.

#throwbackthursday• Work on #28-29 in your green packet independently.

CRT Prep: Life Science #28 L.8.B.5 http://www.rpdp.net/sciencetips_v3/L8B5.htm

The explanation that diseases are caused by microorganisms is known as the

A. cell theory.

B. immune theory.

C. germ theory.

D. infection theory.

CRT Prep: Life Science #29 L.8.B.5 http://www.rpdp.net/sciencetips_v3/L8B5.htm

Exposure to a weakened or mild form of a pathogen to produce immunity is the basis for using a(n)

A. vitamin.

B. interferon.

C. vaccine.

D. antibiotic.

ENERGY VOCABULARY QUIZ

HEAT & THERMAL ENERGY

Thermal Energy

A. Temperature & Heat

1. Temperature is related to the average kinetic energy of the particles in a substance.

2. SI unit for temp. is the Kelvin

a. K = C + 273 (10C = 283K)

b. C = K – 273 (10K = -263C)

3. Thermal Energy – the total of all the kinetic and potential energy of all the particles in a substance.

4. Thermal energy relationships

a. As temperature increases, so does thermal energy (because the kinetic energy of the particles increased).

b. Even if the temperature doesn’t change, the thermal energy in a more massive substance is higher (because it is a total measure of energy).

5. Heat

a. The flow of thermal energy from one object to another.

b. Heat always flows from warmer to cooler objects. Ice gets

warmer while hand gets

cooler

Cup gets cooler while hand gets

warmer

6. Specific Heat

a. Some things heat up or cool down faster than others.

Land heats up and cools down faster than water

b. Specific heat is the amount of heat required to raise the temperature of 1 kg of a material by one degree (C or K).

1) C water = 4184 J / kg C

2) C sand = 664 J / kg C

This is why land heats up quickly during the day and

cools quickly at night and why water takes longer.

Why does water have such a high specific heat?

Water molecules form strong bonds with each other; therefore it takes more heat energy to break them. Metals have weak bonds

and do not need as much energy to break them.

water metal

How to calculate changes in thermal energy

Q = m x T x Cp

Q = change in thermal energy

m = mass of substance

T = change in temperature (Tf – Ti)

Cp = specific heat of substance

c. A calorimeter is used to help measure the specific heat of a substance.

First, mass and temperature of

water are measured

Then heated sample is put

inside and heat flows into

water

T is measured for water to help get its heat gain

This gives the heat lost by

the substance

Knowing its Q value, its mass, and its T, its Cp can be calculated

HEAT TRANSFER

HEAT TRANSFER

I Like it Hot!!

QuestionQ: If a cup of hot chocolate and an ice cube were left on the table in this room what would happen to their Temperature? Why?

A: The cup of hot chocolate will cool until it reaches “room temperature.”

A: The ice cube will melt and then the liquid will warm to “room temperature.”

(Room temperature is about 25 Degrees C)

Heat Transfer• Heat always moves from a warmer place to a cooler

place. • So:

• Hot objects in a cooler room will cool to room temperature.

Heat EnergyHeated liquid/air

Cooler air

The air outside the mug is coolerthan the air inside the mug. So the heated air

moves out of the mug into the cooler air

The cooler air warms up and the mug cools down until both are about equal temperature

Heat Transfer• Heat always moves from a warmer place to a cooler

place. So:• Cold objects in a warmer room will heat up to room

temperature.

Heat Energy

All solids (ice) melt when they gain enough heat energy

Heat Transfer Methods• Heat moves from one place to another by:

•Conduction: Movement through direct contact.

•Convection: Circular motion of heated fluid material.

•Radiation: Light waves through a space or gas.

CONDUCTION:

When you heat a metal strip at one end, the heat travels to the other end.

As you heat the metal, the atoms vibrate faster, these vibrations make the adjacent atoms vibrate, and so on and so on, the vibrations are passed along the metal

and so is the heat.

Metal Bar

So it’s no wonder that you can hold metalover a flame without it burning your hand for

a few seconds, but after that…OUCH!!!

Watch as the atoms closest to theflame gain more energy first and

the energy simply spreads out

Heat Energy

It takes a little time, but the Heat Energy spreads out and the

metal gets “hotter”

Why Metals heat up so fast?

In addition to atom vibrations, the electrons for metal atoms can “drift”; are free to move around

within the metal.

When the metal is heated, the electrons gain kinetic energy and transfer it throughout the metal.

“Insulators”, such as wood and plastic, do not have drifting electrons which is why they do not conduct heat as well as metals.

= electron

HeatEnergy

Why does metal feel colder than wood, if they are both at the same temperature?

Metal is a conductor, wood is an insulator. The metal conducts the heat away from your hands, the wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

The hand holding the metal is losing heatto the metal so it feels cooler!

CONVECTION:

Warmer, less dense liquids and gases (fluids) spread out and rise

up.

Cooler, more dense liquids

and gases (fluids) sink (move down).

= “cool” atom

= “hot” atom

Convection: Movement of Heat in a “circular” motion

Hot water rises

Cooler water sinks

That’s why its called a “Convection Current!”

Cools at the surface

Heat source

Warms back up again.

Hot water rises back

up

Demo: Oil & Thyme

How does this work in a liquid?

A “current” is a “steady flow” of a “fluid” (liquid and gas)

Cold air sinks

Where is the freezer

compartment put in a fridge?

Freezer compartme

nt

It is put at the top, because cool air

sinks, so it cools the

food on the way down.

It is warmer at

the bottom, so

this warmer air rises

and a “convection current”

begins.

Why is it windy at the seaside?

When the cool air reaches the surface of the water, there is nowhere else for it to go

So it moves sideways towards the shore and we feel this motion as a breeze

As the cool breeze reaches the land, it heats up, and rises as well!

And we get convection currents of air!

The third method of heat transfer:

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

RADIATION=The transfer of heat by electro-magnetic waves!

Also Known as “Light!”

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

Radiation helps keep our planet warm

Notice that some of the heat gets “trapped” bythe atmosphere and stays here = planet stays warm!

But some of it escapes back out intoSpace = planet doesn’t warm up too much!

There is a lot of energy in Solar Radiation:

Sunburns are because of Radiation impacting our skin

After the atomic bomb in Japan. There was once a large city where this photo is looking.

Now it is completely destroyed!!! (it only took about 1 second!!!)

Much of this destruction was caused byradiation

There was so much Radiation energy when the bomb blew up that some people

were simply vaporized!!! YIKES!!!

Human Uses for Radiation:• There are some great uses for Radiation;• You can also use radiation to get warm on a camping trip!

Or to cook food with a microwave: