Physical ScienceLecture 46

Instructor: John H. Hamilton

Lecture Review

• Temperature– What temperature is– Temperature scales

• Absolute zero

Temperature

• when most people think of temperature they think of something being either “hot” or “cold” but what is temperature a measure of?

• Temperature is a measure of the average kinetic energy of the molecules of the substance whose temperature is being measured

Temperature continued

• Remember that kinetic energy of a particle depends on its mass and its velocity.

• The motion can be either– Translational– Rotational– Vibrational

Molecular motion diagrams

SI Temperature scale Celsius

• On the Celsius scale 0°C corresponds to the freezing point of water and 100°C corresponds to the boiling point of water at sea level

Fahrenheit scale

• The Fahrenheit scale is an older scale mostly just used in the United States. In this scale water freezes at 32°F and boils at 212°F

• Related to each other

–

Example

• On a hot day the temperature is reported to be 100°F. calculate what the temperature is in celcius

Phases of matter

• Solid• Liquid• Gas• plasma

What happens to matter as its temperature is raised

• Heating a solid will increase the vibration of the molecules until the substance becomes a liquid

• Continue heating the liquid and its temperature increases until the energy levels are such that it turns into a gas

• Continue heating the gas and eventually the molecules break apart, the atoms lose some or all of their electrons and plasma is formed.

• There is NO upper limit for temperature

Absolute zero

• There is no upper limit to temperature but there is a lower limit!

• The lower limit of temperature is called Absolute zero and it occurs at -273°C

Example

• On a cold day the temperture is 10°C BELOW zero. Calculate the temperature in Kelvin (K)

Kelvin scale

• A temperature scale that is used is called the Kelvin scale, named after the scientist Lord Kelvin

• The Kelvin scale is an absolute temperature scale, meaning it is zero at absolute zero

• The kelvin scale has the same incremental change as the Celsius scale

• Water freezes at 273K and boils at 373K

Lecture Review

• viscosity• Bernoulli’s principle

Recommended exercises

• The weatherman says that the low for the night will be 10°F. Calculate the temperature in K

• Go online and look up the surface temperature of the sun. calculate the temperature in F, C, and K

• Explain to someone why there is no Helium in the atmosphere. Make sure they understand.