NOTES 14 - Temperature & Thermal Energy

1. NOTES 14 - Temperature & Thermal Energy

2. What is temperature?

3. What is temperature? • Temperature – The average kinetic energy of the particles in an object or substance • Some particles will be moving faster, some will be slower

4. What is Thermal Energy? • Thermal Energy – the total kinetic energy of the particles in an object or substance • To get it you’d have to add up the motion energy of every particle in an object

5. Which has a higher temperature a cup of hot tea or a lake? • The tea • The lake would be 32 to 80oF • The tea would be 180 to 210oF

6. Which has more thermal energy, the cup of tea or the lake? • The lake • Even though the lake has a lower temperature, the lake has vastly more particles • So the lake’s total energy is greater

8. How do thermometers work? • Thermometers - measure temperature • Different methods and materials can be used to measure temperature: • Expanding liquids • Expanding solids • Electrical conductivity

10. Expanding Liquids? • Some thermometers use expanding liquids (colored alcohol or mercury) • As a substance heats up its particles move faster • This makes the particles move farther apart • So the alcohol expands (gets bigger) as it gets hotter

11. Why expanding metals? • Some thermometers use expanding metals, like copper and iron, sandwiched together • Freezer thermometers use metals because liquids would freeze • Old thermostats use coils of metal attached to a mercury switch to turn the heat on and off

12. Electrical conductivity? • Some thermometers use variations in electric current • Electric current flows faster at lower temperatures • A digital thermometer has a computer sensor that responds to current speeding up or slowing down • New thermostats are digital

13. There are 3 temperature scales • Fahrenheit – used in USA • Celsius – used in most other countries and by scientists • Kelvin – used only by scientists

15. Celsius and Kelvin • Celsius is based on the freezing and boiling points of water • A change of one degree Celsius equals a change of 1.8 degrees Fahrenheit • The Kelvin scale is based on the Celsius scale but starts at absolute zero – 273 degrees below the freezing point of water • A change of one Kelvin equals a change of one degree Celsius

17. What is absolute zero? • Absolute zero - the temperature at which all particle motion stops • So there is no kinetic energy at all • Absolute zero is 0 K which is -273oC • The average temperature of outer space is 3 K (-270oC)

18. Comparison of Temperature Scales