Temperature and Thermal Energy
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Temperature and energy
Glencoe: Chapter 9 – Section 1:
pages 254-259
Temperature and Thermal Energy
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Kinetic Theory of Matter
• The motion of the particles in matter is
described by kinetic theory of matter.
• Matter is
composed of
particles that
are atoms,
molecules, or
ions that always
are in random
motion.
Temperature and Thermal Energy
1
Temperature
• The temperature of a substance is a
measure of the average kinetic energy
of its particles.
• The SI unit for temperature is the
Kelvin (K).
• As kinetic energy increases the
temperature increases
Temperature and Thermal Energy
1
• Here is a
picture
showing the
three
temperature
scales side
by side
Temperature and Thermal Energy
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Temperature
• B. Thermometer –
device that measures
temperature
 Relies on expansion of
heated materials and
contraction of cooled
materials
Temperature and Thermal Energy
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Temperature
1. Liquid thermometers –
glass tube filled with a
liquid
 Limited temperature range
a. Mercury filled
b. Alcohol filled
 Particles move faster as
heated and expand and
rise up the tube
Temperature and Thermal Energy
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Temperature
2. Metal thermometers
 2 bonded strips of metal (2 different metals)
that expand and contract at different rates
 A coiled piece of metal
Temperature and Thermal Energy
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Temperature
• Commonly used temperature scales are
the Celsius (oC) scale, the Fahrenheit (oF)
scale, and the Kelvin (K) scale.
Temperature and Thermal Energy
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Temperature
Energy Transfer (heat and temperature)
- A sense of touch is very important for
determining temperature
- If the temperature of an object is lower than skin
temperature = cold material (ice)
 Energy is transferred from the warmer
material (skin) to the cooler material as
the object’s particles collide with the skin
particles
Temperature and Thermal Energy
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Temperature
• If the temperature of an object is higher
than skin temperature = warm material
(hot water bottle)
 Energy is transferred from the warmer
material to the cooler material (skin) as
the object’s particles collide with the skin
particles
Temperature and Thermal Energy
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Thermal Energy
• The sum of the kinetic and potential
energies of all the particles in an object
is the thermal energy of the object.
• The increase in an
object’s speed
doesn’t affect the
random motion of
its particles, so it
doesn’t affect its
thermal energy.
Temperature and Thermal Energy
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Heat
• Heat is thermal energy that flows from
something at a higher temperature to
something at a lower temperature.
• Heat is a form of energy, so it is measured
in joules.
• The flow of energy always flows from
higher energy (hot) to lower energy
** Warmer will try to “heat up” the cooler**
Transferring Thermal Energy
3
Ways to Transfer Thermal Energy
Conduction
• Energy transfers from one object to another
• This transfer of energy as heat (thermal
energy) as particles collide or objects collide
is called conduction.
• Kinetic energy is transferred when these
faster-moving atoms collide with slowermoving particles.
Transferring Thermal Energy
3
Convection
• Convection is the transfer of thermal
energy in a fluid by the movement of fluid
from place to place.
• Transfer of energy by the movement of
fluids with different temperatures.
• A fluid expands as its temperature increases.
• The density of the fluid therefore decreases.
Transferring Thermal Energy
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Convection Current
• Flow of a fluid due to
heating and cooling
• Warm fluids rise because
they expand and become
less dense (lighter), then
cool.
• The warm water transfers
thermal energy to the cooler
water around it.
Transferring Thermal Energy
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Convection
• As the warm fluids cool,
they contract and get heavier
(denser) and sink.
• As fluids sink they are
warmed up again by the heat
source.
• The rising and sinking
water forms a convection
current.
Transferring Thermal Energy
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Radiation
• Radiation is the transfer of energy
by electromagnetic waves.
• Radiation can pass through solids, liquids,
and gases, but the transfer of energy by
radiation is most important in gases.
• Examples: light, ultraviolet light, infrared
light, sunlight, microwaves, x-rays
• Does not involve the movement of matter.
Transferring Thermal Energy
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Radiation
• When radiation strikes
a material, some energy
is absorbed, some is
reflected, and some
may be transmitted
through the material.
Transferring Thermal Energy
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Conductors and Insulators
1. Conductor – material through which energy
transfers easily
- Examples – metals (energy transfers between
particles easily)
 solids (not all solids) tend to be better
conductors
 gases tend to be poor conductors
Conductors and Insulators
2. Insulator – material that poorly transfers
energy
- Examples – wood, plastic, rubberized
materials, air, water