Physical Science Lecture 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

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.