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Heat

Heat. Particle Model. All matter is in constant motion. Matter has kinetic energy, or energy of motion. The measurement of the average kinetic energy of matter is called temperature. Internal energy is the total amount of energy a substance contains. Galileo Thermometer. Inventors.

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Heat

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  1. Heat

  2. Particle Model • All matter is in constant motion. • Matter has kinetic energy, or energy of motion. • The measurement of the average kinetic energy of matter is called temperature. • Internal energy is the total amount of energy a substance contains.

  3. Galileo Thermometer

  4. Inventors • Anders Celsius, Swedish astronomer, 1701-1744 • Gabriel Daniel Fahrenheit, German-born Dutch instrument maker, 1686-1736

  5. William Thomson, Lord Kelvin • Irish mathematician and physicist, 1824-1907 • His early work led to the future field of cryogenics • Came up with the idea of “absolute zero” – atoms stop moving, take up almost no space and their temperature cannot be lowered any further

  6. How cold can a substance go? • Liquid helium can be cooled to .95 K, 452ºF, or -268.95º C • Absolute zero is 0 K, -459.67ºF or -273ºC. • Liquid helium is used to cool the superconducting magnets in modern MRI scanners. The Large Hadron Collider at CERN uses 96 tons of liquid helium to maintain the temperature at 1.9 Kelvin.[91] • Helium at low temperatures is also used in cryogenics.

  7. How hot can a substance go? • The white dwarf star, NGC 2440, at the center of this planetary nebula, is one of the hottest known objects at 200,000 º C.

  8. Heat flow • Energy transferred from one substance to another is called heat energy. • The official unit of heat energy is the joule.

  9. Heat transfer • Convection: transfer of heat energy by the movement of a fluid, such as a liquid or gas. • Conduction: transfer by direct contact • Radiation: transfer of energy by infrared waves. Can move over long distances. Does not need matter to be transferred.

  10. Infrared imaging

  11. Specific heat • The amount of heat 1 kg of a substance must absorb to raise its temperature 1º C. • Each substance requires a different amount of heat to raise its temperature. • Water has the highest specific heat, 4,185 J/kgº C.

  12. The Heat Equation • Heat = mass x specific heat x change in temperature (∆ Q ) • Example, How much heat is needed to raise the temperature of 0.5 kg of aluminum from 15º C to 20º C? • Solution: mass = 0.5 kg, specific heat of aluminum = 899 J/kgº C and ∆Q = 5º C • Answer: 2247.5 J (some units cancel)

  13. Phase changes

  14. Types of phase changes • Boiling point: liquid to a gas • Melting point/freezing point: solid to a liquid; liquid to a solid • Sublimation: solid directly to a gas • Condensation: gas cooled to a liquid • Evaporation: liquid heated to a gas • Liquid gases have very cold boiling points because a small amount of heat causes them to change to a gas state.

  15. Thermal Expansion

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