Carlos

Science Brain Bogglers (Round 1?)

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I think I may occasionally start posting little science trivia questions or popular science myths and let people argue and discuss to see who gets the correct answer. I find oftentimes in science that deceptively simple questions can yield a disproportionate amount of understanding when answered.

First of all, here are the rules: no internet resources may be consulted, and you may not participate if you already know the answer.

First question: If heat rises, why does it get colder the higher you travel in Earth's atmosphere?

Again, if you've already learned the answer behind this, please refrain from ruining the fun for other people who don't know the answer and will want to try and reason it out.

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Ok, what I think is that air is not affected by the sun nearly as much as the earth is. I think this is because the heating of an object has to do with friction from movement of molecules caused by light waves. The moving, dispersed air therefore stays cooler than the dense earth. So the main source of hot air is not directly the sun but the earth. The air is heated on the surface then rises into the unheated air and eventually cools back down.

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First question: If heat rises, why does it get colder the higher you travel in Earth's atmosphere?

Again, if you've already learned the answer behind this, please refrain from ruining the fun for other people who don't know the answer and will want to try and reason it out.

What is "heat?"

It's molecular motion. The higher you travel away from the earth, the thinner the atmosphere which means fewer molecules which means less molecular motion which means less heat.

How's that for a non-scientist?

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I appreciate the answers so far :angry2:

More information on the format of this: I think I will delay making comments on the validity of the answers so far because I do not want to bias or infringe on the independence of the thought processes of other participants who may answer. I will periodically (maybe every day or so?) give an update as to whether anyone has correctly answered the question or not. After an appropriate period of time the "game" will end and I will announce the winner or give the answer myself.

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I love this game!

[...]I will delay making comments on the validity of the answers so far because I do not want to bias or infringe on the independence of the thought processes of other participants who may answer.

?

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I love this game!
[...]I will delay making comments on the validity of the answers so far because I do not want to bias or infringe on the independence of the thought processes of other participants who may answer.

?

What I mean is that I want to let everyone who wants to participate to have their fun and develop their own reasoning before I begin to make corrections or start saying who's on the right track with their answers and who isn't. I want each person's answers to be uniquely their own, because the point is after all for people to practice their reasoning on scientific questions.

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Clue: Have you ever pumped up a bicycle tire and noticed that the compressed air made the pump hot?

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Clue: Have you ever pumped up a bicycle tire and noticed that the compressed air made the pump hot?

Just to be picky, please don't give clues or hints; if you want to play just give your own reasoned answer.

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What is "heat?"

It's molecular motion. The higher you travel away from the earth, the thinner the atmosphere which means fewer molecules which means less molecular motion which means less heat.

How's that for a non-scientist?

I need to be picky here on definitions, and make sure two concepts aren't being confused (heat and temperature). My question was why does the atmosphere get colder the higher you travel, and by this I mean colder temperature.

The temperature of a substance is a measure of the average kinetic energy of the particles (atoms, molecules) that compose it; higher temperatures means a faster "wiggling" of those particles, lower temperatures means a slower wiggling. So it doesn't matter how dense something is in regards to its temperature; what matters is the kinetic energy of the atoms and molecules that compose that substance, and therefore everything from the air to the comparably dense brick walls of your apartment can all have the same temperature. The same would be true for our atmosphere: just because our atmosphere becomes "thinner" with greater height doesn't mean the temperature must change with height simply because of that.

Heat, depending on the context, has multiple meanings. The most common everyday meaning of heat is the physical perception of warmth or hotness. Metal with a temperature of 110F will feel much hotter than air at 110F; the reason for this is that metal is much more dense than air, and can conduct heat energy to our skin much more rapidly than air can. Likewise, this is the same reason that 65F water feels really cold while 65F air only feels slightly cool; the much denser water is a much greater conductor of heat energy, and it can cool you off much more rapidly than air alone.

If by heat you mean the amount of thermal energy a substance has, then that will depend on the substance. A block of metal will contain much more heat energy than an equal volume of air at an equal temperature; this is simply because the metal is much more dense (there are more atoms/molecules per volume).

So yes, as you climb higher in the Earth's atmosphere and as the air becomes "thinner", the air will contain less heat energy per volume than at sea-level, but this alone says nothing about how the temperature will change with altitude. The question I am looking for to be answered is why the temperature is lower at higher altitudes.

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Ok, what I think is that air is not affected by the sun nearly as much as the earth is. I think this is because the heating of an object has to do with friction from movement of molecules caused by light waves. The moving, dispersed air therefore stays cooler than the dense earth. So the main source of hot air is not directly the sun but the earth. The air is heated on the surface then rises into the unheated air and eventually cools back down.

The Earth's atmosphere absorbs very little to none of the incoming sun-light; what dominantly absorbs sunlight is the Earth itself, the ground we walk on. This heats up the ground (raises its temperature) and from direct heat conduction the air in contact with the surface of the Earth is heated. This mechanism is the source of the majority of the heat energy in our atmosphere. So you can imagine that our atmosphere is a giant section of air that is floating on a "hot-plate" which is the Earth.

In this sense you are on the right track, but I'm not sure what you mean by the first few sentences... sunlight contains energy, and when an object absorbs sunlight it gains the energy that comes with it, and that energy becomes heat in the substance itself.

But your answer cannot be the entire story. Consider this: if the floor of my apartment were a giant hot-plate that heated the air, with enough time all the air in my apartment would be roughly equal in temperature to the hot-plate. Why doesn't this ever happen with the Earth?

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The Earth's atmosphere absorbs very little to none of the incoming sun-light; what dominantly absorbs sunlight is the Earth itself, the ground we walk on.

I dug out a textbook on Meteorology and want to correct part of this using an example from the text.

If 100 units of solar energy hit the Earth, then

35 is reflected back to space (24 reflected from clouds, 7 scattered from air, 4 reflected from ground)

14.5 is absorbed in the troposphere (the lower layer of the atmosphere where weather events happen and we live)

3 is absorbed in the stratosphere (layer above troposphere)

47.5 is absorbed by the ground.

On an interesting note, the surface radiates 114.5 upwards in the form of long-wave radiation. 109 units are absorbed by H2O and CO2, and 5.5 escape to space. This means that the atmosphere is already nearly perfectly opaque to the long-wave radiation emitted by the Earth, and you can't expect extra CO2 to do much more greenhouse effect than what it already does. (you can't get more opaque than opaque...).

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In this sense you are on the right track, but I'm not sure what you mean by the first few sentences...

"...air is not affected by the sun nearly as much as the earth is..." This refers to what you saying about the atmosphere not absorbing as much of the incoming light. I was not sure of the theory on why this is true and that is what my next sentence about the different densities was trying to take care of.

But your answer cannot be the entire story. Consider this: if the floor of my apartment were a giant hot-plate that heated the air, with enough time all the air in my apartment would be roughly equal in temperature to the hot-plate. Why doesn't this ever happen with the Earth?

First, I think that the part of the earth in the shade keeps some of the air cooling instead of heating at all times. Also, the parts of the earth that are never hit directly by the sun such as the north and south poles are surrounded by cooler air. This cooler air, both from cold places and places in the shade, is not stationary and moves around the globe, preventing the above situation from happening.

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Also, the parts of the earth that are never hit directly by the sun such as the north and south poles are surrounded by cooler air. ---------

Not sure what you mean by directly here. The Polar regions are in sunlight for 6 months of the year and in darkness for 6 months of the year. If by direct you mean the rays are perpendicular to the surface, then only the area between the Tropics gets direct sunlight.

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I was not sure of the theory on why this is true and that is what my next sentence about the different densities was trying to take care of.
Other than the nitrogen gas in our atmosphere strongly scattering blue light (which is why we get red sunsets and a blue sky!) the air itself absorbs almost no incoming radiation. What does absorb some of the incoming radiation is water vapor and maybe some dust particles.
But your answer cannot be the entire story. Consider this: if the floor of my apartment were a giant hot-plate that heated the air, with enough time all the air in my apartment would be roughly equal in temperature to the hot-plate. Why doesn't this ever happen with the Earth?

First, I think that the part of the earth in the shade keeps some of the air cooling instead of heating at all times. Also, the parts of the earth that are never hit directly by the sun such as the north and south poles are surrounded by cooler air. This cooler air, both from cold places and places in the shade, is not stationary and moves around the globe, preventing the above situation from happening.

You bring up good points here, but even this cannot completely account for why it is colder at higher elevations.

The intense sunlight at the equator and sparse sunlight at the poles does drive a global atmospheric circulation, but this cannot contribute to the atmosphere being colder at higher altitudes. If anything it would help to keep the atmosphere isothermal, by constantly overturning the different layers of warmer/colder air.

How does the atmosphere actually cool on the nightside of the Earth? Outer space may be extremely cold, but it is close to vacuum, so there is nothing to conduct the heat away from the Earth.

You had mentioned earlier that rising warm air would encounter cold air, so the rising air would cool off and sink back down. But in doing so the cold air should be constantly gaining heat energy and warming up. Why doesn't the atmosphere eventually become isothermal?

Thank you for your thoughts so far :angry2:

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Ok, what I think is that air is not affected by the sun nearly as much as the earth is. I think this is because the heating of an object has to do with friction from movement of molecules caused by light waves. The moving, dispersed air therefore stays cooler than the dense earth. So the main source of hot air is not directly the sun but the earth. The air is heated on the surface then rises into the unheated air and eventually cools back down.

The Earth's atmosphere absorbs very little to none of the incoming sun-light; what dominantly absorbs sunlight is the Earth itself, the ground we walk on. This heats up the ground (raises its temperature) and from direct heat conduction the air in contact with the surface of the Earth is heated. This mechanism is the source of the majority of the heat energy in our atmosphere. So you can imagine that our atmosphere is a giant section of air that is floating on a "hot-plate" which is the Earth.

In this sense you are on the right track, but I'm not sure what you mean by the first few sentences... sunlight contains energy, and when an object absorbs sunlight it gains the energy that comes with it, and that energy becomes heat in the substance itself.

But your answer cannot be the entire story. Consider this: if the floor of my apartment were a giant hot-plate that heated the air, with enough time all the air in my apartment would be roughly equal in temperature to the hot-plate. Why doesn't this ever happen with the Earth?

Because there is no roof to contain the heat. All objects will tend to equilibrate with their surroundings, and the earth's surrounding is outer space which is quite cold, I believe. If it is hot outside (summer), and you turn off your air conditioner, it gets hot inside the room.

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----------

------

Also, the parts of the earth that are never hit directly by the sun such as the north and south poles are surrounded by cooler air. ---------

Not sure what you mean by directly here. The Polar regions are in sunlight for 6 months of the year and in darkness for 6 months of the year. If by direct you mean the rays are perpendicular to the surface, then only the area between the Tropics gets direct sunlight.

The incident radiation though strikes the Earth with greatest intensity around the equator, and diminishes to nearly zero as you move towards the poles. This is the dominating factor behind why it gets colder closer to the poles.

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Because there is no roof to contain the heat. All objects will tend to equilibrate with their surroundings, and the earth's surrounding is outer space which is quite cold, I believe. If it is hot outside (summer), and you turn off your air conditioner, it gets hot inside the room.

But outer-space is the greatest possible thermal insulator you can have! There is physically nothing there (almost) to conduct heat away.

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How does the atmosphere actually cool on the nightside of the Earth? Outer space may be extremely cold, but it is close to vacuum, so there is nothing to conduct the heat away from the Earth.

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Forms of heat transfer: conduction, convection, radiation. Heat escapes earth by radiation. All objects above absolute 0 degrees radiate heat.

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I think I may occasionally start posting little science trivia questions or popular science myths and let people argue and discuss to see who gets the correct answer. I find oftentimes in science that deceptively simple questions can yield a disproportionate amount of understanding when answered.

First of all, here are the rules: no internet resources may be consulted, and you may not participate if you already know the answer.

First question: If heat rises, why does it get colder the higher you travel in Earth's atmosphere?

Again, if you've already learned the answer behind this, please refrain from ruining the fun for other people who don't know the answer and will want to try and reason it out.

Heat rises because it is less dense than cold air: in effect, it has more buoyancy. So it is a given that it will cool as it equilibrates with the surrounding air above it.

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Heat rises because it is less dense than cold air: in effect, it has more buoyancy. So it is a given that it will cool as it equilibrates with the surrounding air above it.

But why doesn't the colder air warm as the warmer air equilibrates, over time causing it all to become isothermal?

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How does the atmosphere actually cool on the nightside of the Earth? Outer space may be extremely cold, but it is close to vacuum, so there is nothing to conduct the heat away from the Earth.

You had mentioned earlier that rising warm air would encounter cold air, so the rising air would cool off and sink back down. But in doing so the cold air should be constantly gaining heat energy and warming up. Why doesn't the atmosphere eventually become isothermal?

This is how I think the atmosphere cools on the nightside of the Earth. You mentioned that "65F water feels really cold while 65F air only feels slightly cool; the much denser water is a much greater conductor of heat energy, and it can cool you off much more rapidly than air alone." The Earth is a greater conductor of heat energy than the air. When the sun is no longer heating up the surface, the Earth begins to loose the heat energy. As it is cooling off, it absorbs what heat energy is in the air around it, cooling it down as well. Basically the earth warms up and cools down quicker than the air and directly controls the temperature of the air around it.

So one side of the Earth is heating the air while the other side is cooling the air and the atmosphere cannot become isothermal.

But this leads to the problem that the lower you are the cooler it would be when it is night. This is not right, correct? I will have to give this problem some more time.

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Heat rises because it is less dense than cold air: in effect, it has more buoyancy. So it is a given that it will cool as it equilibrates with the surrounding air above it.

But why doesn't the colder air warm as the warmer air equilibrates, over time causing it all to become isothermal?

The warm air does warm the cooler air above it. It can only become isothermal if it is in a closed system. As I said before, without a roof covering the earth, heat his radiated to space. Thus, there is a long term tendency for the atmosphere to cool. But that doesn't mean that, locally, warm air can not be above cooler air due to air currents in the atmosphere, such as warm air over the ocean moving over land that has cooler air, or warm air over land moving over cooler air over the ocean.

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How does the atmosphere actually cool on the nightside of the Earth? Outer space may be extremely cold, but it is close to vacuum, so there is nothing to conduct the heat away from the Earth.

You had mentioned earlier that rising warm air would encounter cold air, so the rising air would cool off and sink back down. But in doing so the cold air should be constantly gaining heat energy and warming up. Why doesn't the atmosphere eventually become isothermal?

This is how I think the atmosphere cools on the nightside of the Earth. You mentioned that "65F water feels really cold while 65F air only feels slightly cool; the much denser water is a much greater conductor of heat energy, and it can cool you off much more rapidly than air alone." The Earth is a greater conductor of heat energy than the air. When the sun is no longer heating up the surface, the Earth begins to loose the heat energy. As it is cooling off, it absorbs what heat energy is in the air around it, cooling it down as well. Basically the earth warms up and cools down quicker than the air and directly controls the temperature of the air around it.

So one side of the Earth is heating the air while the other side is cooling the air and the atmosphere cannot become isothermal.

But this leads to the problem that the lower you are the cooler it would be when it is night. This is not right, correct? I will have to give this problem some more time.

Very good points. You may be right.

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