# Will CO2 absorb photon in all directions?

Discussion in 'Physics & Math' started by Robittybob1, Mar 16, 2012.

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1. ### BelieveHappy mediumValued Senior Member

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Even if I am very wrong here on that point and the radiation pushes them all in the same initial direction what happens to that motion the first time they collide with something?

Drop the box of ping pong balls straight down onto the ground, They all initialy go the same direction (towards the floor) but when they hit something they go all over the place. The same thing would happen as the orintation of each molecule will be different when they hit eachother.

O=C=O

The molecule will be spinning on its own axis, would you not agree that different orinentations would produce different results if they collided with something in the same direction? Drop a pencil 10x head on, 10x flat, and 10x slanted and see for yourself it goes the same way each time.

3. ### waitedavid137Registered Senior Member

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That's because the momentum transfer is very small. You actually have to do the experiment under very controlled conditions to observe it as per example Nichols radiometer torsion balance.

5. ### BelieveHappy mediumValued Senior Member

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So then this motion would not be enough to counter act the motion imparted by absorbion and collisions, correct?

7. ### waitedavid137Registered Senior Member

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If I understand what you are asking correctly then right. Thats why a Crook's radiometer runs backwards.

8. ### BelieveHappy mediumValued Senior Member

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So you see Robittybob1 , even though I am wrong about the photos ability to impart motion directly (my bad, again I am not a physics student), it's contribution is not enough to cause the molecules to move in the exact same direction without being much stronger then the sun. Perhaps if their initial velocity is 0, but then they would be frozen solid.

Basically the motion it already has is a car going down the road and the direct push of a photon is that squirrel it just ran over.

Last edited: Apr 15, 2012
9. ### waitedavid137Registered Senior Member

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Right, but the engine also runs on squirrel power, lol.
Electrons of the atoms and molecules absorb light photons, the primary effect of importance is to put them into a higher energy state. For example a water molecule which is a greenhouse gas by the way could have its hydrogen atoms knocking around more rapidly now and when it comes into contact with a less excited molecule it can transfer energy and now significant momentum transfer but in random direction. So the main effect of the sun light is to just generally heat up the atmosphere and end in more chaotic motion of the molecules. The momentum transfer of the absorbed light is not a significant impact on the end result by any stretch.

10. ### BelieveHappy mediumValued Senior Member

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How many spm(squirrels per mile) does such an engine get?

11. ### Robittybob1BannedBanned

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I like you @Believe for you don't give up too quickly, and you have set your mind on trying to understand how I have come to understand that the miniscule amount of momentum in a photon when applied in the right way is enough to get a planet in the order 10^25 kg to spin faster.

And that is how it was for me too, for the thought of it is bizarre to start with. But if you add all the power that falls on a planet and converted that to kinetic energy you see there is just no problem for the Sun is the power source, and the atmosphere is medium through which this acts.

But the issue then becomes - how do you make the momentum which appears initially to be affecting the planet equally on both limbs of the planet, and the resulting collisions so random, how does that add up to a net force powering up a planet?

A tonne of ping pong balls having a common direction would knock you over just like a tonne rocks. The momentum is conserved, and if there is common direction to begin with that net momentum in the end result still reflects the initial direction of the tonne of balls.

12. ### Robittybob1BannedBanned

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But that is what I do believe, the net momentum can affect a planet's rotation rate in the order of a few miliseconds per year, which then multiplied over the billions of years adds up to significant changes in day length.

13. ### waitedavid137Registered Senior Member

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Its the interaction of an excited molecule with another that kicks off equally opposite momentum transfer in random direction.

14. ### BelieveHappy mediumValued Senior Member

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OK, now I give up, 2 people that you say you can listen to are telling you that this not the case. It generates 2 types of momentum, the push force which is small compaired to the random collision force which is large by compairison. The net (i.e. overall) result is still random.

The point of the ping pong balls is not that they can all go in the same direction, but in the fact that once they hit you they go in a random direction.

A molecule of air would not make it all the way from the upper atmosphere down to the surface to hit the earth, it will hit other molecules along the way. Even if it did as a direct result of the heating the push would be straight on pushing the earth further out of orbit rather then causing it to spin.

If you want to talk about the ones that would not be straight on, the ones close to the edge of the planet, they would be balence out by those on the other side of the edge(I.E. the same amount would be happening on the western edge as the eastern edge making the net motion 0)

15. ### OnlyMeValued Senior Member

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I think that to some extent the potential for a direct transfer of momentum was covered earlier. A reference to a practical experiment demonstrating the potential can be found in the last paragraph of, How does a light-mill work?

On a last note, it is possible to measure radiation pressure using a more refined apparatus. One needs to use a much better vacuum, suspend the vanes from fine fibers and coat the vanes with an inert glass to prevent out-gassing. When this is done, the vanes are deflected the other way &mdash as predicted by Maxwell. The experiment is very difficult; it was first done successfully in 1901 by Pyotr Lebedev and also by Ernest Nichols and Gordon Hull.

In the example of the refined radiometer, what is being demonstrated is the difference in the transfer of momentum between reflective and carbon black surfaces. However, one cannot exclude that there is momentum transferred to both surfaces, at unequal rates. Since the refined mechanism does demonstrate a momentum transfer directly from the photons. It must be assumed that there is some momentum transfer potential in all photon particle — or atom/molecule interactions.

16. ### waitedavid137Registered Senior Member

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What was the calculation that inferred this?
Its actual slowing rate which is due to angular momentum transfer to the moon due to Earth's odd shape with continents, is every year a day takes ~0.01ms (a lot smaller than your guess) longer than a day took to complete the previous year. So 4 billion years ago a day took ~13 hrs. The estimates rough and the rate won't be exactly constant really but this gives you an idea on the real numbers and where they come from.

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18. ### Robittybob1BannedBanned

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At this stage it is an insight. I have this idea that is how it could happen. The Sun has the power, but we are now looking for the mechanism. Currently I'm looking at the way CO2 would absorb different strength photons on either side of a spinning planet (The effects of red-shift and blue-shift come into it too). The planet that seems too be the classic example in Venus where the winds rotate the planet faster than the planets spin.
The friction between the atmosphere must be transferring momentum to the planet, but the wind has not stopped. There is some mechanism that keeps powering up the winds. It can't be the Coriolis Effect as the planet rotates so slowly.

The Earth is not a planet that is as easy to see the effects, with the Moon and a fairly rapid rotation.

We definitely haven't got the maths worked out yet.

19. ### Robittybob1BannedBanned

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@ Believe - The the thing about conservation of momentum is that the momentum is conserved no matter how many odd collisions are subsequently observed. You start looking at the macroscopic rather than the microscopic aspects in the end result.

20. ### Robittybob1BannedBanned

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Last edited: Apr 16, 2012
21. ### BelieveHappy mediumValued Senior Member

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That does not mean what you think it means, conserved means the same amount of energy is present, not that is the same type of energy or in the same direction. But again I am done.

22. ### Robittybob1BannedBanned

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I think you need to stick with this discussion for you are making the same mistakes I was making.

Momentum and Energy are not the same thing. Momentum is always conserved but energy is not. (Not conserved in the motion in inelastic collisions.)

23. ### BelieveHappy mediumValued Senior Member

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http://en.wikipedia.org/wiki/Conservation_of_energy

Is is in fact a law of physics