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?
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
Units
Water freezes
Water boils
Body temp
Fahrenheit oF
32 oF
212 oF
98.6 oF
Celsius oC
0 oC
100 oC
37 oC
Kelvin
Kelvins (K)
273K
373K
310 K