Vocabulary Thermal Energy – The SUM of all the molecular movement in a substance Temperature – The AVERAGE of the molecular movement in a substance.

Vocabulary

Thermal Energy – The SUM of all the molecular movement in a substance

Temperature – The AVERAGE of the molecular movement in a substance

WarmupConsider the free body diagram. If the

sum of the tension forces is equal to

the force of gravity, which description

BEST applies?

A) A book is at rest on a tabletop.

B) A physics student rests a backpack upon one shoulder.

C) A girl hangs by both hands, motionless, from a trapeze.

D) A girl falls slowly to Earth while strapped to a

parachute.

Explanation A girl hangs by both hands,

motionless, from a trapeze.If the forces are equal and opposite, there is no motion. There is not one but two tension forces work when a girl hangs by both hands, as illustrated by the two upward arrows in the free body diagram. Resting a backpack on your shoulder would be represented by only one tension force arrow.

S8P2. Students will be familiar with the forms and transformations of energy.

d. Describe how heat can be transferred through matter by the collisions of atoms (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection).

S8P1. Students will examine the scientific view of the nature of matter.

c. Describe the movement of particles in solids, liquids, gases, and plasmas states.

Temperature

The measure of the average kinetic energy (KE) of the particles in an object.

Can be measured in degrees Celsius (°C), degrees Fahrenheit (°F), or kelvins (K).

One kelvin is the same size as one Celsius degree.

Temperature

The lowest temperature on the Kelvin scale is 0 K, about -459 °F, which is called absolute zero: the temperature at which all molecular motion stops.

It is not actually possible to reach absolute zero, although temperatures very close to 0 K have been reached in laboratories.

Temperature

Temperature As the temperature of an

object increases, the average speed (KE) of the particles in random motion increases.

The temperature of a substance does not depend on how much of it you have.The temperature of the tea

in the cup is the same as the temperature of the tea in the teapot, even though there is more tea in the teapot.

Thermal Energy The sum of the kinetic and potential

energy of all the particles in an object○ KE - movement of particles○ PE - forces within or between particles due

to position Depends on:

○ Temperature○ Mass○ Type of substance

Thermal energy increases as temperature increases.

Thermal Energy and Mass The more particles there

are in a substance at a given temperature, the greater the thermal energy of the substance is.

Although both soups are at the same temperature, there is more soup in the pot. So, the soup in the pot has more thermal energy than the soup in the bowl.

Thermal Energy Which beaker of water has more thermal

energy?B - same temperature, but more mass

200 mL

80ºC

A400 mL

80ºC

B

Thermal Expansion An increase in the size of a substance in

response to an increase in the temperature of the substance.

As temperature increases, particles move faster and spread out, leaving room for expansion.The opposite is known as contraction.

Examples: expansion joints on bridges, bimetallic strips in thermostats, hot air balloon.

Thermal Expansion

Expansion Joints on BridgesThe gaps in the bridge

allow the concrete to expand (during warmer temperatures) and contract (during colder temperatures) without breaking.

Thermal Expansion Bimetallic Strips in Thermostats

A bimetallic strip is made of two different materials stacked in a thin strip.

Because different materials expand at different rates, one of the metals expands more than the other when the strip gets hot, making the strip coil and uncoil. This opens and closes the circuit to make the heater turn off or on.

Thermal Energy and States of Matter

Matter exists in four states or phases:

Solids

Liquids

Gases

Plasmas

Thermal Energy and States of Matter

SOLID LIQUID GAS PLASMA

Tightly packed in a regular pattern;

Vibrate, but do not move from place

to place

Close together with no regular arrangement;Vibrate, move

about, and slide past each other

Well-separated with no regular arrangement;

Vibrate and move freely at high

speeds

Has no definite volume or shape and is composed

of electrical charged particles

Heat Thermal energy that flows from

something at a higher temperature to something at a lower temperature

Like work, heat is:measured in joules (J)a transfer of energy:

○ the amount of heat transferred depends on the difference in temperature between the objects.

Heat TransferWhy does A feel hot and B feel cold?

80ºC

A

10ºC

B

Heat flows from A to your hand = hot. Heat flows from your hand to B = cold. Heat flows until temperatures are equal (equilibrium).

Warmup Conductor : A substance that transfers

thermal energy easily

Insulator : A substance the prevents or slows down the transfer of thermal energy

Warmup – Unit 1 Review The Smith family is travelling in their car at

50 km/h due east. Mr. Smith is using cruise control to maintain a constant speed. Describe the net force acting on the Smith car.

A)Net force equals zero. B)Net forces are unbalanced. C)Net force is positive and to the east. D)There is no way to determine net force.

Explanation

Net force equals zero. When an object travels at a constant speed in a straight line, the acceleration is zero. There is no change in speed or direction; that means no change in velocity. When an object is experiencing a net force of zero, it will continue to move at a constant velocity.

Heat TransferThermal energy (heat) is

transferred in three ways:

Conduction – through matter by the collision of atoms (direct contact)

Radiation – through matter or space by electromagnetic (EM) waves

Convection – through liquids or gases by convection currents

Conduction (Thermal Conduction) The transfer of The transfer of

thermal energy from thermal energy from one substance to one substance to another by collisions another by collisions between the between the particles in matter particles in matter ((direct contactdirect contact). ). Occurs most often Occurs most often

in solidsin solids

• Thermal energy is transferred when one end of a metal spoon is heated by a Bunsen burner.

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

As you heat the metal, the particles vibrate. These vibrations make the adjacent particles vibrate, and so on and so on. The kinetic energy of these particles and the heat is passed along the metal. We call this conduction.

ConductionConduction

Conduction

Thermal Conductor Thermal Conductor – material that – material that easily transfers heateasily transfers heat

Most Most metalsmetals are good conductors. are good conductors. Ex. Copper, silver, iron, steel, aluminum, glass Ex. Copper, silver, iron, steel, aluminum, glass

In a piece of metal, there are electrons that are not bound to individual atoms, but can move easily through the metal.

Collisions between these electrons and other particles in the metal enable thermal energy to be transferred more quickly than in other materials.

Thermal Insulator Thermal Insulator – material that reduces

or prevents the transfer of heatNonmetals, wood, some plastics, fiberglass,

Styrofoam, paper, and air are good insulatorsMaterials, such as metals, that are good

conductors of heat are poor insulators.

Thermal Insulator Gases, such as air, are

usually much better insulators than solids or liquids.

Some types of insulators contain many pockets of trapped air.

Building insulation is usually made of some fluffy material, such as fiberglass, that contains pockets of trapped air.

The insulation is packed intoa building’s outer walls andattic, where it reduces theflow of heat between thebuilding and the surroundingair.

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

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

Thermal Conductor vs. Thermal Insulator

Convection Convection - the transfer of heat by

circulation or movement of currents in a liquid or gas

Convection occurs mostly in liquids and gases.

“Heat rises” is another way to think about convection.

Examples:Warmer water at the surface of a

lake or swimming poolWind currentsHot air balloonLower floors of a building being

cooler than the top floor

What happens to the particles in a liquid or a gas when you heat them?

The particles spread out and become less dense.

This effects fluid movement. A fluid is a liquid or a gas.

Convection

• Cooler, denser fluids sink through warmer, less dense fluids.

• In effect, warmer liquids and gases rise up.

• Cooler liquids and gases sink.

Convection

• As water is heated, it becomes less dense. The warmer water rises through the cooler water above it.

• At the surface, the warm water cools and becomes more dense. The cooler water then sinks to the bottom and the cycle repeats.

• Convection currents transfer heat from warmer to cooler parts of the fluid.

• In a convection current, both conduction and convection transfer thermal energy.

Convection

Hot water rises

Cooler water sinks

Convection current

Cools at the surface

Convection

Convection

Convection

Radiation Radiation – the transfer of energy

by electromagnetic waves through empty space or matter.

An electromagnetic wave is a wave that can travel through empty space or matter and consists of changing electric and magnetic fields.

Energy is transferred from the Sun to Earth through radiation even though no matter is present.

Heat energy can travel through a vacuum through radiation.

Examples: A camp fire A microwave oven A light bulb

Radiation

?

Radiation• Air close to the ground is warmed by conduction.

• The warmer air then rises by convection.

• However, since there are no particles between the Sun and the Earth, heat CANNOT travel by conduction or by convection.

•In nature, the Sun warms the Earth through radiation.•Land warms faster than water.

RADIATION

Radiation When radiation strikes a material, some of the energy is

absorbed, some is reflected, and some may be transmitted through the material.

The amount of energy absorbed, reflected, and transmitted depends on the type of material.

Materials that are light-colored reflect more radiant energy, while dark-colored materials absorb more radiant energy.

Radiation The transfer of energy by radiation is most important in gases. In a solid, liquid, or gas, radiant energy can travel through the space

between molecules. Molecules can absorb this radiation and emit some of the energy

they absorbed.

Identify the Type of Heat Transfer That is Shown