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Chapter 10 Heat and Temperature. Temperature How hot or cold something is. How hot or cold something is. What make something hot? What make something.

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Presentation on theme: "Chapter 10 Heat and Temperature. Temperature How hot or cold something is. How hot or cold something is. What make something hot? What make something."— Presentation transcript:

1 Chapter 10 Heat and Temperature

2 Temperature How hot or cold something is. How hot or cold something is. What make something hot? What make something hot? Particles that me up matter are in constant motion Particles that me up matter are in constant motion They have kinetic energy They have kinetic energy When you heat something the particles move faster When you heat something the particles move faster Temperature measures average KE Temperature measures average KE

3 Temperature Measured with thermometers Measured with thermometers Most materials expand when heated. Most materials expand when heated. That is how most thermometers work That is how most thermometers work Liquid thermometers have a large bulb hooked to a narrow tube. Liquid thermometers have a large bulb hooked to a narrow tube. When the liquid expands it rises up the tube. When the liquid expands it rises up the tube. Wont work if too hot or cold Wont work if too hot or cold

4 Thermometers Metals expand when heated Metals expand when heated Different metals expand different amounts Different metals expand different amounts Hook two metals together to make a thermometer that turns Hook two metals together to make a thermometer that turns Bimetallic Thermometers Bimetallic Thermometers Iron Copper Hot Cold

5 Thermometers Bimetallic thermometers are used in thermostats Bimetallic thermometers are used in thermostats Digital thermometers use the fact that electricity conducts differently at different temperatures. Digital thermometers use the fact that electricity conducts differently at different temperatures.

6 Temperature As the temperature get lower the molecules move slower As the temperature get lower the molecules move slower Kinetic energy goes down Kinetic energy goes down Lowest possible temperature would be when molecules stop moving Lowest possible temperature would be when molecules stop moving Absolute zero Absolute zero

7 Temperature Scales Three different ones get used Three different ones get used Fahrenheit- the one we use Fahrenheit- the one we use Celsius- metric standard Celsius- metric standard Kelvin- starts at absolute zero but same degree size as Celsius Kelvin- starts at absolute zero but same degree size as Celsius

8 Converting Temperature F = 9 C F = 9 C K = C K = C Water freezes at 32°F, what is this in Celsius? Water freezes at 32°F, what is this in Celsius? In Kevin? In Kevin? Water boils at 100°C. What is this in Fahrenheit? Water boils at 100°C. What is this in Fahrenheit? In Kelvin? In Kelvin?

9 0C0C32F 273 K

10 0C0C32F 273 K 100C212F 373 K

11 0C0C32F 273 K 100C212F 373 K -273C-492F 0 K

12 Conversion Practice Body temperature is 98.6°F, what is this in Celsius? In Kelvin? Body temperature is 98.6°F, what is this in Celsius? In Kelvin? Methanol boils at 75°C, what is this in Fahrenheit?, in Kelvin? Methanol boils at 75°C, what is this in Fahrenheit?, in Kelvin? Lead melts at 600 K, what is this in Celsius? In Fahrenheit? Lead melts at 600 K, what is this in Celsius? In Fahrenheit?

13 Temperature tells you direction That energy will move. That energy will move. Always moves from high temperature to low temperature. Always moves from high temperature to low temperature. Faster molecules (high temperature) hit slower molecules (low temperature) and speed them up Faster molecules (high temperature) hit slower molecules (low temperature) and speed them up

14 Energy Transfer Heat can be transferred 3 different ways Heat can be transferred 3 different ways Conduction- transferred by direct contact Conduction- transferred by direct contact Molecules of high temperature object move faster, hit slower molecules so they speed up Molecules of high temperature object move faster, hit slower molecules so they speed up Doesnt work well in gases, too far apart Doesnt work well in gases, too far apart Works better in liquids, but still not well Works better in liquids, but still not well Works well in some solids Works well in some solids

15 Energy Transfer Conductors- materials that allow heat to pass through them Conductors- materials that allow heat to pass through them Most metals Most metals Insulators- materials that dont let heat through them well Insulators- materials that dont let heat through them well Rubber, plastics, glass Rubber, plastics, glass Insulation traps air in pockets. Insulation traps air in pockets. Still air makes a good insulator. Still air makes a good insulator.

16 Energy Transfer Convections- transferring energy by moving fluids Convections- transferring energy by moving fluids Liquids and gases are fluids Liquids and gases are fluids When heated they expand, become less dense When heated they expand, become less dense They rise, replaced by cooler denser fluids They rise, replaced by cooler denser fluids Make a circular flow called a convection current Make a circular flow called a convection current

17 Convection Current Hot Air Rises Cool Air Sinks

18 Energy Transfer Radiation- Energy transferred by electromagnetic waves Radiation- Energy transferred by electromagnetic waves Can travel through empty space Can travel through empty space When wave hit object they make the molecules move faster. When wave hit object they make the molecules move faster.

19 Specific Heat Some materials heat up easily Some materials heat up easily Others require a large amount of energy to change their temperature Others require a large amount of energy to change their temperature Specific heat measures the amount of energy required to raise the temperature 1 kg of a substance by 1 degree Kelvin Specific heat measures the amount of energy required to raise the temperature 1 kg of a substance by 1 degree Kelvin Table on page 336 Table on page 336 Water has a high specific heat Water has a high specific heat 4186 J/kg K 4186 J/kg K

20 Specific Heat Metals have a low specific heat Metals have a low specific heat Iron 449 J/kg K Iron 449 J/kg K Heat = Specific heat x mass x change in temp Heat = Specific heat x mass x change in temp How much heat does it take to change the temperature of 3 kg of water by 75 K? How much heat does it take to change the temperature of 3 kg of water by 75 K? How much heat to change the heat of 5 kg of iron by 75 K? How much heat to change the heat of 5 kg of iron by 75 K?


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