Science Buddies: "Ask an Expert"

HI,

I did this activity in my science book to see how it gets hotter inside a car
compared to the outside. Basically I had two aquariums, one with the top covered
and a thermometer inside and the other aquarium with the top open and a thermometer inside.
I also placed a third thermometer outside (it said in the activity to do so).
I noticed that the temperature inside the aquarium
with the top closed was higher than the one with the open top.
The temperature noted in the thermometer placed outside was almost the same
as the one in the aquarium with the top open.
Based on this is it right to conclude that the temperature inside the car
gets much higher because the heat cannot escape by convection and it is not due to greenhouse effect?
Please help because I have to give my project outline on Monday
Thank you very much,
Rachel

Hi Rachel. My apologies that no one got back to you sooner.

Actually, your car heating up when it has been sitting out on a hot day, just as your aquarium experiment, is a perfect example of the greenhouse effect. The concept is that light and heat (energy) are entering the car / aquarium through the glass, but not all the energy is escaping. In a way, our earth's atmosphere works the same way. The earth's land and water absorbs some of the heat, but some heat is also reflected back into outer space. The earth's atmosphere (consisting of water and gases such as carbon dioxide) prevents some of this heat from escaping the earth.

Here are a couple of articles to get you started. I just googled "hotter inside car and greenhouse effect." If you do this, you'll find a lot more resources.
http://science.howstuffworks.com/enviro ... rming2.htm
http://www.epa.gov/climatechange/kids/greenhouse.html

Please feel free to write back with follow-up questions. Good luck!

Unfortunately, "The Green House Effect" as it applies to the earth has become a lot more political than scientific.

If you look at actual "Green Houses" intended for growing plants inside in a warmer environment than the outside climate, a car with its windows rolled up sitting in the sun heats up the same way plant growing green houses do. Some of the radiated heat energy from the sun passes through the glass and is absorbed by darker materials in the car which warms them up which in turn warms up the air inside the car.

The parked car with its engine off and its windows rolled up is a fairly well sealed environment so one can come up with a fairly accurate thermodynamic model for the heat exchanges using some college level math that will accurately predict the internal temperature changes.

The earth is a lot more massive and not as well sealed. The earth's atmosphere is collecting and sheding particles all the time. Because it is so big and we know a lot less about it as a whole and know even less about all the external influences in the space around the earth, coming up with an accurate model is beyond our current level of knowledge or ability to model in sufficient detail. To understand how inaccurate this can be, how often are the weather predictions as to how much rain any small area is going to get in any 5 minute period?

Thank you both Craig and Deana for your inputs.
I will do some more background research and will
post questions. Thanks again. The links are very informative.

Rachel

A more physics and opticals oriented answer:

Energy from the sun arrives as shorter-wave energy, such as visible light and infra-red light. These can pass through the air rather easily and when they strike the earth they heat it. You can feel this when you are in bright sunlight or near a big hot object such as a fire, stove, or furnace.

Part two: After an object is heated, it reradiates energy the same way, but at a wavelength that is proportional to its temperature. Sunlight is from a10,000 degF sun surface. The hot object on earth has radiation proportional to about 80 degF, which is a much longer wavelength. The greenhouse effect occurs when the greenhouse's cover is opaque to this longer wavelength light and blocks it, thus trapping the heat (the energy).

The open aquarium has two methods of cooling, reradiation, but more importantly, air circulation. In the case of the earth as a planet, there is no air circulation out into space, the air on earth stays on earth and all the energy reradiated has to go out as light. The air circulation on earth is why the tropics and the poles are within 200 degF of each other instead of 700 degF.

When you hear about temperature extremes in space, it is exactly the same thing, solar heating on the hot side, radiating into space on the cold side, and with no air to moderate things.

Bob