# Amount of energy on Earth doesn't grow or shrink

## Main Question or Discussion Point

I am not quite sure if this is the right area to post this thread, but I know that energy on our planet comes from the Sun, which constantly supplies the planet with this energy. Since the sun gives a constant supply to us, in order to keep our plants alive, shouldn't the amount of energy on our planet increase further and further untill it burns out? After all, the Law of Conservation of Energy states that energy cannot be created, nor destroyed. Also, to my knowledge, our planet does not heat up space, so where would the extra energy go? According to my science teacher, the amount of energy on Earth doesn't grow or shrink. Is he wrong?

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mgb_phys
Homework Helper
Our planet does heat up space.
The hotter an object gets, the more heat it radiates and so it cools.
Our planet's temperature is simply set by the equilibrium between the rate at which we get energy from the sun and the rate we radiate it out into space.
The atmosphere, plants etc merely change the amount of the suns radiation that gets absorbed rather than simply bouncing off.

Not only that, but theres a delicate balance between Geothermal energy as well. We generate our own heat, the sun gives us heat, and we (Earth) must emit an equal amount of that energy in the form of UV radiation at the same rate in order to avoid becoming a planetary oven like Mercury and Venus.. Theres a coefficient somewhere in there that accounts for the conversion of em energy into chemical energy I'm sure.. It's really an interesting topic of study!

ive actually wondered this myself... if the heat is being radiated into space... wouldnt there have to be a medium for the heat (from earth) to exchange into? Another thing i thought about is that if energy and matter are one in the same is it possible that some of the energy from the sun is actually converted to matter when it gets here actually making the mass of the earth slightly greater?

"if the heat is being radiated into space... wouldnt there have to be a medium for the heat (from earth) to exchange into?"

You said the magic word in that same sentence ... 'radiated.'
Anything with a temperature will emit black body radiation, and this is a way for the earth to give off heat.

"Another thing i thought about is that if energy and matter are one in the same is it possible that some of the energy from the sun is actually converted to matter when it gets here actually making the mass of the earth slightly greater?"

I assume you're referring to the famous E = mc^2 . I'm not very certain as how to correctly word this, but it's more a way of saying everything with mass has an inherent energy: the rest mass times c^2. If you add energy to that particle, you therefore increase its mass; this is the relativistic mass.

Integral
Staff Emeritus
Gold Member
Not only that, but theres a delicate balance between Geothermal energy as well. We generate our own heat, the sun gives us heat, and we (Earth) must emit an equal amount of that energy in the form of UV radiation at the same rate in order to avoid becoming a planetary oven like Mercury and Venus.. Theres a coefficient somewhere in there that accounts for the conversion of em energy into chemical energy I'm sure.. It's really an interesting topic of study!
Are you sure about UV radiation? I would suspect that it is in the form of IR.

Ya the earth will emit IR seens a simple consideration of blackbody radiation tells you that the earth will admit light at the frequency corresponding to its temperature and the temperature of the earth's surface is approximately room temperature which is in the IR range

"admit light at the frequency corresponding to its temperature"

Doesn't it just peak in a frequency corresponding to temperature?

mgb_phys
Homework Helper
"admit light at the frequency corresponding to its temperature"
Doesn't it just peak in a frequency corresponding to temperature?
For a blackbody the entire emission spectrum is determined only by temperature.
There is also a simple relationship between peak emission wavelength and temperature (wien's law)

I'm sorry, I wasn't very clear. There's a curve with a smaller slope, then a peak in a certain range, then a sharp dropoff?

mgb_phys
Homework Helper
I'm sorry, I wasn't very clear. There's a curve with a smaller slope, then a peak in a certain range, then a sharp dropoff?
Depending which direction you are reading, and if you are plotting wavelenght or frequency!
In a black body there is a steep drop off at shorter wavelenghts - a room temperature body doesn't emit much visible or UV, then a peak (wien's law) then a long slow tail to longer wavelenghts. As you heat something the total power goes up and the peak shifts to shorter wavelengths but the shape remains the same.

So if you assume something is a blackbody and know it's temperature you know it's emission at all wavelengths.

Nice question,

We are on a knife edge balance that could be disastrously tipped in the wrong direction if serious action is not taken by humanity now, rather than later.

Global warming

regards

Alan

seycyrus
Nice question,

We are on a knife edge balance that could be disastrously tipped in the wrong direction if serious action is not taken by humanity now, rather than later.

Global warming

regards

Alan
Or not...