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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