Iceland Volcanoes!

The Thermal Energy of a substance is the total energy of all of its molecules and

atoms. It consists of both the potential and kinetic energy of the molecules of the

substance as they vibrate back and forth. Physics people usually call this internal

energy.

Temperature Scales

Fahrenheit freezing at 32o, boiling at 212o

Celsius freezing at 0o, boiling at 100o

Absolute C + 273o

There is not an absolute upper limit for temperature….the temperature inside of many stars is over 30 million

degrees, and even higher temperatures are likely inside supernovas and black holes…

The is an absolute lower limit. Gas samples (like the air inside a balloon) change their volume based on the

temperature. At –273oC the volume of a gas sample will go to zero – this means basically that all molecular energy

stops! We have been within a few tenths of a degree of this temperature, but will have difficulty actually reaching

it.

-273oC = 0o Kelvin = Absolute Zero!

When pressure is held constant, the volume of a gas changes (decreases) by 1/273 for each degree C the

temperature decreases.

gas

piston

Zero volume!

An assortment of absolute temperatures

Some Definitions….

Matter can contain thermal energy (or internal energy).

Heat is the flow of thermal energy – from a hotter object to a cooler one. Heat is thermal energy in transition.

High Thermal Energy Low Thermal Energy

Heat!

There is no such physical property as Cold…..

Cold is simply the absence of heat!

How do we measure Heat??

Heat is a form of energy. A physics person measures heat in a unit called a Joule.

We use a different unit:

A calorie is the amount of heat required to to raise the temperature of 1 gram (1 cm3 or 1 ml) of water by 1oC.

A Calorie (like we look at on the candy bar wrapper!) is really 1000 calories!

Specific Heat Capacity

The crust and the filling of the pie come out of the oven at the same temperature….. but the crust cools much more quickly. If you bite into a big bite of pie, you’ll probably burn your mouth!

The part of the pie that has a lot of liquid (which is water!) “holds” its heat much longer than the crust.

Some substances take more heat to warm up than others, and, once warmed, take longer to cool (give up their heat!)

It takes much more energy to warm up a kilogram of water than it does a kilogram of

oil! (or wood, air, glass, etc…!)

The Eastern Shore has cooler summers and milder winters than the western shore because the Bay stores and gives up energy slowly , and the winds usually blow from

west to east across it…

Ocean current provide the major mechanism to transfer the excess of solar thermal energy from the tropics to

the polar regions.

“Day after Tomorrow” web link

When molecules of a substance are heated, they gain energy and “move” faster. This makes them push

apart from each other and the volume of the substance expands. (volume is how much space

something takes up!)

This is called Thermal Expansion, and must be considered by engineers and architects!

Not allowing for thermal

expansion can cause

problems…..

What’s wrong with this picture??

The base of a land-based bridge has one side which can move!

Most bridges have expansion joints which allow the sections of the bridge to move relative to each other. The Bay Bridge has these…

“bi-metallic”strips can be used in thermostats to turn a device on or off as temperature changes

An old-ish thermostat!

Unique Properties of Water

As water cools to near the freezing point, ice crystals start to form in it – decreasing the density because the

molecules move further apart as ice forms!

The water molecules (H2O) in ice are farther apart than they are in water. This makes the

density of ice LESS

Density = mass/volume!

Normally, substances become more dense as they

cool, and water does until it gets to

4oC – at which point ice crystals start to form and

density decreases!

This makes fish very happy…

Happy Fish…