NOTES 14 - Temperature & Thermal Energy
What is temperature?
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
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
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
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
How do thermometers work? Thermometers - measure temperature Different methods and materials can be used to measure temperature: Expanding liquids Expanding solids Electrical conductivity
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
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
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
There are 3 temperature scales Fahrenheit – used in USA Celsius – used in most other countries and by scientists Kelvin – used only by scientists
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
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)
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