Friday, February 6, 2009

At the start of the lesson, Mr Heah did a revision of what we had done last week.

Firstly, he talked about systems and that all systems must have a balance, equilibrium or in biology terms, homeostasis. When the system is not at equilibrium, either a negative or a positive feedback occurs. Negative feedbacks discourages change and hence the change would be stable. Positive feedback encourages change and hence the change would be unstable.

Then Mr Heah started talking about the main gist of our lesson, which was on thermodyanic equilibrium.

Heat transfers in 3 ways: conduction, convection and radiation.

The range of visible light: Red Orange Yellow Green Blue Indigo Violet

Short wavelengths -------------------> long wavelengths

cool ---------------------------------------> hot

low energy ------------------------------> high energy

The sun emits long wavelengths and the Earth emites short wavelengths.

So, what does thermodynamic equilibrium mean?

It simply just means heat gained by the Earth, must be equal to the heat lost by the Earth.

However, due to an excess in greenhouse gases, we are losing less heat because greenhouse gases trap heat within the atmosphere.

Mr Heah then talked about CO2 which is a greenhouse gas. CO2 absorbs long wave radiation but allows short wave radiation which comes from the sun to pass through. So greenhouse gases actually act as a heat blanket for the Earth.

Global warming is due to the building up of more greenhouse gases which then traps more heat.

To see exactly how much heat is gained and lost and in what ways, Mr Heah got us to draw this diagram. It shows exactly how much heat is gained and lost and how if the Earth gains 100 units of heat.

That's all for now (:

-audrina