Thermal Energy

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Thermal Energy
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Bellringer 57

• Write down the following questions to be answered
  after the video.
• 1. What do calories measure?
• 2. What observation is made in the video?
• 3. What was different about the cheese puffs and
  the toasted oats when they were burned?

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Temperature

• All particles in an object are constantly in
  motion therefore, each object has kinetic energy.
• Temperature is a measure of the average kinetic
  energy of the particles in an object.
• As the kinetic energy of an object increases, the
  temperature of an object increases.
• In SI units, temperature is measured in Kelvin
  (K).

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Motion of Particles
The particles in an object are in constant random
motion. Particles move faster in hotter objects
than in cooler objects.
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How is Temperature Measured?

• Thermometers are used to measure temperature.
• Thermometers work on the principle of thermal
  expansion.
• As the temperature increases most objects expand
  due to an increase in kinetic energy. With
  increased kinetic energy, the particles in
  objects move farther apart (expand).
• Due to this expansion, the liquid in a
  thermometer moves upward.

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Thermal Energy

• The feeling associated with temperature
  difference results from energy transfer.
• Changes in temperature involve changes in energy,
  but thermal energy and temperature are not the
  same.
• Thermal energy is the sum of all the kinetic and
  potential energies of the particles in an object.
• The amount of thermal energy depends on mass,
  temperature, and amount of energy a material
  stores per degree.

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Thermal Energy (2)

• The thermal energy of an object increases as its
  temperature increases.
• If the temperature doesnt change, the thermal
  energy in an object increases if the mass of an
  object increases.

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Heat

• A transfer of energy between the particles of two
  objects due to a temperature difference is heat.
• Heat always flows from a warmer object to a
  cooler object.
• The greater the difference in the temperatures of
  two objects, the more energy that will transfer.

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Calculating Heat

• Heat capacity is the capacity of any amount of
  material to absorb energy.
• If you are at the beach, which absorbs the most
  radiant energy, the ocean or the beach sand?
• As a substance absorbs heat, its temperature
  change depends on the nature of the substance, as
  well as the amount of heat added.
• Compared to a 1 kg of sand, the amount of heat
  that is needed to raise the temperature of 1 kg
  of water by 1oC is about six times greater.

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Calculating Heat (2)

• Specific heat is the amount of heat required to
  raise the temperature of 1 kg of a material by 1
  oC.
• Like density, specific heat is a characteristic
  physical property of a substance.
• Specific heat is measured in joules per kilogram
  degree Celsius. J/(kg oC)

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Specific Heat of Common Materials
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Measuring Specific Heat

• The specific heat of a material can be measured
  using a device called a calorimeter.
• In a calorimeter, a heated sample transfers heat
  to a known mass of water.
• The energy absorbed by the water can be
  calculated by measuring the waters temperature
  change.
• The thermal energy released by the sample equals
  the thermal energy absorbed by the water.

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Measuring Specific Heat (2)
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Measuring Specific Heat (3)

• Water has a very high specific heat, which is why
  it is used as a coolant.
• It takes more energy to increase the temperature
  of water than for other substances in nature.

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Changes in Thermal Energy

• The thermal energy of an object changes when heat
  flows in or out of the object.
• The following equation can be used to calculate
  thermal energy

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Temperature, Thermal energy, Heat, Specific heat,
Conduction, Convection, Radiation, Insulator,
Solar collector, Thermodynamics, First Law of
Thermodynamics, Second Law of Thermodynamics,
Heat engine, Internal combustion engine
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Heat Flow

• Heat flow is the movement of heat from areas of
  higher temperature to areas of lower temperature.
• This heat flow may occur in three ways through
  conduction, convection, and radiation.

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Conduction

• Conduction is the transfer of thermal energy by
  collisions between particles in matter.
• Conduction occurs because particles in matter are
  in constant motion.
• Conduction takes place when two objects that are
  in contact are at unequal temperatures.
• Suppose you place one end of a metal spoon in a
  flame. The kinetic energy of the particles near
  the flame increases.
• Kinetic energy is transferred when these
  particles collide with neighboring particles.

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Conduction (2)

• Thermal energy is transferred by collisions
  between particles with more kinetic energy and
  those with less kinetic energy.
• Eventually due to the collisions, the other end
  of the spoon is heated.
• When heat is transferred by conduction, thermal
  energy is transferred without transferring matter.

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Conduction (3)

• Conduction occurs within a material as
  faster-moving particles transfer thermal energy
  by colliding with slower-moving particles.

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Conductors

• Any material through which energy can be
  transferred as heat is called a conductor.
• Solids are the best conductors, especially
  metals.

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Convection

• Convection is the transfer of thermal energy in a
  fluid (liquid or gas) by the movement of warmer
  and cooler fluid from place to place.
• When convection occurs, more energetic particles
  move from one place to another.
• As particles move faster, they tend to be farther
  apart so a fluid expands as temperature
  increases.
• Therefore, the density of a warmer fluid is less
  than that of the surrounding cooler fluid.

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Convection (2)

• Due to differences in density, the warmer fluids
  (less dense) rise and the cooler fluids (more
  dense) sink.
• The cycle is called a convection current.
• Convection causes the weather patterns on Earth.

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Convection (3)

• When the oil in the lamp is cool, its density is
  greater than that of the alcohol, and it sits at
  the bottom of the lamp. When the two liquids are
  heated, the oil becomes less dense than the
  alcohol. Because it is less dense than the
  alcohol, it rises to the top of the lamp. As it
  rises, it loses heat by conduction to the cooler
  fluid around it. When the oil reaches the top of
  the lamp, it has become cool enough that it is
  denser than the alcohol, and it sinks. This
  rising and sinking action is a convection
  current.

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Radiation

• Radiation is the transfer of energy by
  electromagnetic waves.
• These waves can travel through space even when no
  matter is present.
• This type of heat travels outward from its source
  in all directions.
• Energy that is transferred by radiation is often
  called radiant energy.
• Heat from the Sun warms Earth by radiation.

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Radiation (2)

• When radiation strikes a material, some of the
  energy is absorbed, some is reflected, and some
  may be transmitted through the material. This
  figure shows what happens to radiant energy from
  the Sun as it reaches Earth.
• Materials that are light-colored reflect more
  radiant energy, while dark-colored materials
  absorb more radiant energy.

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Radiation (3)

• Radiation can pass through solids, liquids, and
  gases.
• Because particles are much farther apart in gases
  than in liquids or solids, radiation usually
  passes more easily through gases than through
  solids or liquids.

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Insulators

• A material in which heat flows slowly is an
  insulator.
• Examples of materials that are insulators are
  wood, some plastics, fiberglass, and air.
• A thermos bottle uses a vacuum and reflective
  surfaces to reduce the flow of heat into and out
  of the bottle.
• The vacuum prevents heat flow by conduction and
  convection.
• The reflective surfaces reduce the heat transfer
  by radiation.