Heat and Temperature

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Heat and Temperature
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Objectives

• Define temperature in terms of the average
  kinetic energy of atoms or molecules.
• Convert temperature readings between the
  Fahrenheit, Celsius, and Kelvin scales.
• Describe heat as a form of energy transfer.
• investigate how energy is transferred.
• Distinguish between conductors and insulators.

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Temperature is

• A measure of the kinetic energy of all the
  particles within an object.
• As the average kinetic energy of an object
  increases, its temperature will increase.

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Particles in an object
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Low temperature
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High temperature
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Questions

• Can a glass of water and a lake have the same
  average kinetic energy?
• Can a glass of water and a lake have the same
  total energy?

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Answers

• A glass of water and a lake have the same average
  kinetic energy (the kinetic energy of the water
  molecule is the same).
• A glass of water has less total kinetic energy
  than a lake, due to the smaller number of water
  molecules in a glass.

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How do we measure temperature?

• By using a device that measures temperatures.
• Thermometer.
• Thermometers are based on a simple principle .
• That most objects expand when their temperature
  increases.

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Types of Thermometers

• Liquid thermometers use mercury or colored
  alcohol.
• Metal thermometers use metal strips.
• Digital thermometers use changes in electricity .

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Scales used for measuring temperatures

• Fahrenheit.
• Celsius.
• Kelvin.

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Fahrenheit

• Most familiar in the United States.
• The units are F.
• On the Fahrenheit scale, water freezes at 32F
  and boils at 212F.
• There are 180 spaces in between water freezing
  and boiling.

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Celsius

• Other countries use the Celsius scale.
• It gives a value of zero to the freezing point of
  water and a value of 100 to the boiling point.
• There are 100 spaces between water boiling and
  freezing.

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Kelvin

• Used in many fields of science.
• The Kelvin is based on the temperature known as
  absolute zero.
• Absolute zero is the temperature at which an
  objects energy is minimal.
• On the Kelvin scale, 0 Kelvin is absolute zero.

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How to convert from Celsius to Fahrenheit?

• Use the Celsius-Fahrenheit equation.
• Fahrenheit temp.(9/5xCelsius temp.)32
• Example
• Convert 60C to Fahrenheit.
• (9/5 x 60) 32 140F

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How to convert from Fahrenheit to Celsius?

• Use the Fahrenheit-Celsius equation.
• Celsius temp. 5/9(Fahrenheit temp. -32)
• Example
• Convert 70F to Celsius.
• 5/9(70-32)21C

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How to convert between Kelvin and Celsius?

• Use the Celsius-Kelvin Equation.
• Kelvin temp. Celsius temp. 273

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Todays Inquiry Lab

• How do temperature and energy relate?
• The objective is to relate temperature to energy
  transfer.

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HEAT

• The transfer of energy from the particles of one
  object to those of another object due to a
  temperature difference between the two objects.

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Examples of heat transfer

• Painful sensation of a burn is caused by a rapid
  transfer of energy as heat.
• Grabbing a piece of ice causes heat energy
  transfer from your hand to the ice.
• Stepping into a hot bath causes heat energy
  transfer from the hot water to your feet.
• Popping popcorn is an example of heat transfer.

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Methods of Energy Transfer

• Conduction.
• Convection.
• Radiation.

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conduction

• The transfer of energy as heat between particles
  as they collide within a substance or between two
  objects in contact.
• Conduction involves objects in direct contact.
• Example metal rod you use to roast your
  marshmallow on a fire becomes warm at the end
  that youre holding.

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convection

• The transfer of energy by the movement of fluids
  with different temperatures.
• While roasting your marshmallow on the fire, you
  notice tiny glowing embers rise and swirl.
• The embers are following the movement of air,
  which rises and falls because of convection
  currents.

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Radiation

• The transfer of energy by electromagnetic waves.
• Radiation does not require physical contact
  between objects.
• The warmth you feel when youre standing near the
  fire is due to radiation in the form of
  electromagnetic waves.

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radiation

• Radiation is the only method of energy transfer
  that can take place in a vacuum, such as outer
  space.
• The energy we receive from the sun is transferred
  by radiation.

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Question

• How does a lizard on a rock in the desert
  increase its body temperature? What two methods
  of heat energy transfer are involved?

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Answer

• Cold-blooded animals, such as lizards and
  turtles, increase their body temperature by using
  external sources, such as the sun.
• During basking, energy is absorbed by the lizard
  by its skin through conduction from the warmer
  rocks, and by radiation from sunlight.

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Energy Transfer
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Insulators

• Materials that are poor energy conductors.
• Insulators slow the transfer of energy as heat.
• Wood is an insulator.

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Conductors

• Materials through which energy can be easily
  transferred as heat.
• Gases are poor conductors of heat.
• Liquids conduct heat better than gases, but they
  are not very effective conductors.
• Solids such as iron, copper, and silver are good
  conductors.

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Todays Inquiry Lab

• What color absorbs more radiation?
• The objective is to study radiation as a form of
  heat transfer.