Vocabulary

Thermal Energy – The SUM of all the
molecular movement in a substance

Temperature – The AVERAGE of the
molecular movement in a substance
Warmup
Consider 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
80ºC
A
80ºC
B
200 mL
400 mL
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
Bridges
 The 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
Tightly packed in
a regular pattern;
Vibrate, but do not
move from place
to place
LIQUID
Close together
with no regular
arrangement;
Vibrate, move
about, and slide
past each other
GAS
Well-separated
with no regular
arrangement;
Vibrate and move
freely at high
speeds
PLASMA
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 Transfer

Why does A feel hot and B feel cold?
 Heat flows from A to your hand = hot.
 Heat flows from your hand to B = cold.
 Heat flows until temperatures are equal (equilibrium).
80ºC
A
10ºC
B
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 Transfer
Thermal 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
thermal energy from
one substance to
another by collisions
between the
particles in matter
(direct contact).
 Occurs most often in
solids
• Thermal energy is
transferred when
one end of a
metal spoon is
heated by a
Bunsen burner.
Conduction
• When you heat a metal strip at one end, the heat
travels to the other end.
Conduction
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.
Thermal Conductor

Thermal Conductor – material that easily transfers heat
 Most metals are good conductors.
 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 heat
 Nonmetals, wood, some plastics, fiberglass,
Styrofoam, paper, and air are good insulators
 Materials, 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 into
a building’s outer walls and
attic, where it reduces the
flow of heat between the
building and the surrounding
air.
Thermal Conductor vs. Thermal Insulator
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.
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 pool
 Wind currents
 Hot air balloon
 Lower floors of a building being
cooler than the top floor
Convection
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
Cools at the
surface
Cooler
water sinks
Convection
Convection
current
Hot water
rises
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