If enough heat is applied to an object, will it reach escape speed?

[Remon]

This is just something I'm wondering, if we apply enough heat to an object, and since the speed of the molecules inside it is directly measured by temperature, will the molecules inside the object move fast enough to reach the escape speed of the planet that it is on? I know that this is the case for why many planets don't have an atmosphere (because their escape speed is too low to hold an atmosphere due to their weak gravity) and I'd also think that when enough heat is applied to a solid object, it turns into a gas and (if heated enough) will continue rising up above the planet's surface until it "breaks free" of the planets gravity, thus, reaching escape velocity. Although, I don't know if these assumptions are true.

 

[gabriel.dac]

Uhh no. If you apply heat to an object, it will vibrate more. You won't change it's speed.
However, heated gas becomes more dilated, so, depending on the mass of the planet, it can escape - but not because it reached escape velocity

Also, the correct term is escape velocity, not speed.

 

[ZapperZ]

This is just something I'm wondering, if we apply enough heat to an object, and since the speed of the molecules inside it is directly measured by temperature, will the molecules inside the object move fast enough to reach the escape speed of the planet that it is on? I know that this is the case for why many planets don't have an atmosphere (because their escape speed is too low to hold an atmosphere due to their weak gravity) and I'd also think that when enough heat is applied to a solid object, it turns into a gas and (if heated enough) will continue rising up above the planet's surface until it "breaks free" of the planets gravity, thus, reaching escape velocity. Although, I don't know if these assumptions are true.

I don't know what you mean by "escape speed" here, but you might want to look up "thermionic emission". That is a common electron source used in old TV and CRT tube and old diodes. The heated filament is the electron source.

However, applying this to celestial bodies is a completely different matter and physics.

Zz.

 

[Remon]

Uhh no. If you apply heat to an object, it will vibrate more. You won't change it's speed.

Also, the correct term is escape velocity, not speed.

What? I'm talking about the molecules moving faster (in km/s for gasses) inside the object if it is being heated, not the actual object moving as a whole... well, it does move as a whole through states
I learned that from a homework assignment that I had for astronomy - the question talked about the moon Titan and the molecules inside its atmosphere having a speed of about 0.4 km/s (while Titan's escape velocity is 2.6 km/s I think), the question asked me to compare the molecules' speed with Titan's escape velocity and the speed needed for the molecules in its atmosphere to evaporate (or move faster than Titan's escape velocity so that they evaporate/escape Titan)

 

[Remon]

I don't know what you mean by "escape speed" here, but you might want to look up "thermionic emission". That is a common electron source used in old TV and CRT tube and old diodes. The heated filament is the electron source.

However, applying this to celestial bodies is a completely different matter and physics.

Zz.

I mean the escape velocity (you guys get too hung up on terminology, I know its important too but try to focus more on the meaning) of a planet, and I also don't see what "thermionic emission" have to do with what I'm asking, it would be helpful if you can elaborate.

 

[ZapperZ]

I mean the escape velocity (you guys get too hung up on terminology, I know its important too but try to focus more on the meaning) of a planet, and I also don't see what "thermionic emission" have to do with what I'm asking, it would be helpful if you can elaborate.

First of all, I wasn't the one who was "hung up" on the terminology.

Secondly, I was giving an example of how electrons can escape a solid simply via heat, which is analogous to what you were asking.

Thirdly, you might want to consider the fact that "objects" melt or vaporize at some point as you increase the temperature. So consider the average KE at those critical temperatures.

Finally, molecules, atoms, and particles of such size do not have free, unimpeded travel from Earth's surface to the upper atmosphere to escape, even if it has enough speed to escape the Earth's gravity in the first place. The presence of air means that it will have a mean free path that is sufficiently short, it won't be able to travel far before it encounters collisions with other particles.

Zz.

 

[gabriel.dac]

What? I'm talking about the molecules moving faster (in km/s for gasses) inside the object if it is being heated, not the actual object moving as a whole... well, it does move as a whole through states
I learned that from a homework assignment that I had for astronomy - the question talked about the moon Titan and the molecules inside its atmosphere having a speed of about 0.4 km/s (while Titan's escape velocity is 2.6 km/s I think), the question asked me to compare the molecules' speed with Titan's escape velocity and the speed needed for the molecules in its atmosphere to evaporate (or move faster than Titan's escape velocity so that they evaporate/escape Titan)

I see that english is not your native language. It is not my native language either, but anyway, that question does not make any sense. Titan's atmosphere is made out of gas (obviously, duh). So how can it evaporate? And what does speed have to do with that? Only liquids can evaporate

 

[Remon]

First of all, I wasn't the one who was "hung up" on the terminology.

Secondly, I was giving an example of how electrons can escape a solid simply via heat, which is analogous to what you were asking.

Thirdly, you might want to consider the fact that "objects" melt or vaporize at some point as you increase the temperature. So consider the average KE at those critical temperatures.

Finally, molecules, atoms, and particles of such size do not have free, unimpeded travel from Earth's surface to the upper atmosphere to escape, even if it has enough speed to escape the Earth's gravity in the first place. The presence of air means that it will have a mean free path that is sufficiently short, it won't be able to travel far before it encounters collisions with other particles.

Zz.

So what you mean is that when molecules obtain more speed due to the increased temperature, they will just collide more with each other and not actually change their place as a 'whole'? Because I was thinking that the reason why gasses rise in the air is because their molecules are moving faster than a solid or a liquid object on the ground (which I think leads to lighter or heavier density, but that's another story), which also means that the faster the molecules move (or the higher the temperature), the higher the gas will rise above the surface; although, I could (and probably) be completely wrong, which is why I'm asking you guys. And also, I did "consider the fact that 'objects' melt", I stated in a previous post that "objects move through states".

 

[Remon]

I see that english is not your native language. It is not my native language either, but anyway, that question does not make any sense. Titan's atmosphere is made out of gas (obviously, duh). So how can it evaporate? And what does speed have to do with that? Only liquids can evaporate

Here is the question exactly: "Saturn’s moon Titan is the only moon in the solar system with an atmosphere, which is 95% nitrogen molecules (N₂), similar to Earth’s atmosphere. At Saturn’s distance from the Sun, the temperature of the atmosphere is only 95 K (−180^◦ C), and the molecules have an average speed of about 0.4 km/s. How does this speed compare with the speed needed for the molecules to escape from Titan and evaporate into space? Show how you got your answer."

p.s I've been speaking English for over 8 years now, so I'll try not to take that as an insult (I also don't see how my English is inferior in anyway, but that's not the focus here).

 

[ZapperZ]

Here is the question exactly: "Saturn’s moon Titan is the only moon in the solar system with an atmosphere, which is 95% nitrogen molecules (N₂), similar to Earth’s atmosphere. At Saturn’s distance from the Sun, the temperature of the atmosphere is only 95 K (−180^◦ C), and the molecules have an average speed of about 0.4 km/s. How does this speed compare with the speed needed for the molecules to escape from Titan and evaporate into space? Show how you got your answer."

p.s I've been speaking English for over 8 years now, so I'll try not to take that as an insult (I also don't see how my English is inferior in anyway, but that's not the focus here).

This appears to be a HW/Coursework-type question. If this is the impetus of your question, then you've posted it in the wrong section. You should have started with this in the very beginning, rather than asking a rather puzzling question, and you should have posted this in the HW/Coursework forum.

Zz.

 

[russ_watters]

Regardless of the framing, the question points to a discussion of how our atmosphere got its current composition:
The molecular weight and temperature of molecules does indeed determine their speed and if the speed is high, they can indeed escape. That's why our atmosphere has few light gases and Mars is almost entirely carbon dioxide.

For large objects, there is no bulk motion, so the idea does not apply.

Confused framing or not (that's why the question is being asked!), this is not a complicated or controversial enough subject to have been worthy of such aggressive replies. Calm down and consider who you are talking to, people.

 

[Remon]

This appears to be a HW/Coursework-type question. If this is the impetus of your question, then you've posted it in the wrong section. You should have started with this in the very beginning, rather than asking a rather puzzling question, and you should have posted this in the HW/Coursework forum.

Zz.

... Ok, here's what happened: I started with this question about a week ago and I needed help with it so I did post it in the homework section to ask for help. But, after I finished the assignment and got all the help I needed (a few days ago), I started thinking more about the question and thought that the concept implied in the question (which is the relation between molecules' speed and escape velocity) could also be applied to all objects. So, to feed my own curiosity, I decided to post the question that I thought of here (in this section), but my question originated from the assignment question that I posted, but it is not directly related to it at all.

 

[russ_watters]

Also, the correct term is escape velocity, not speed.

I prefer "escape speed" because "escape velocity" wrongly implies that direction matters.

 

[Remon]

Regardless of the framing, the question points to a discussion of how our atmosphere got its current composition:
The molecular weight and temperature of molecules does indeed determine their speed and if the speed is high, they can indeed escape. That's why our atmosphere has few light gases and Mars is almost entirely carbon dioxide.

That's exactly what I was saying, that "if the speed is high, they can indeed escape" the celestial body that they are on. Therefore, with high enough temperature (combined with low molecular weight), a gas can reach and go beyond escape velocity, right? But what I'm not sure of is that if escape velocity can be reached by the increased speed of molecules (within the gas), which would lead the gas to escape from the planet.

 

[Remon]

Confused framing or not (that's why the question is being asked!), this is not a complicated or controversial enough subject to have been worthy of such aggressive replies. Calm down and consider who you are talking to, people.

I know that that is not directly aimed at me but I apologize if I was being aggressive in any way (which I'm sure I wasn't), that is not my goal here.

 

[gabriel.dac]

Regardless of the framing, the question points to a discussion of how our atmosphere got its current composition:
The molecular weight and temperature of molecules does indeed determine their speed and if the speed is high, they can indeed escape. That's why our atmosphere has few light gases and Mars is almost entirely carbon dioxide.

Oh, so basically what you are saying is that hotter gases will get less dense and will move faster towards space, right? If so, Ramon's question makes sense. But if you heat the whole atmosphere equally, nothing will happen but dilation.

 

[jbriggs444]

Oh, so basically what you are saying is that hotter gases will get less dense and will move faster towards space, right? If so, Ramon's question makes sense. But if you heat the whole atmosphere equally, nothing will happen but dilation.

The point is that lighter gasses (such as hydrogen and helium) at a given temperature will have a larger fraction of their component molecules at a speed greater than escape velocity. So you can heat the atmosphere evenly and while most or all of hydrogen can escape [over geological time periods] the fraction of the carbon dioxide that escapes over the same period will be much less.

 

[Remon]

The point is that lighter gasses (such as hydrogen and helium) at a given temperature will have a larger fraction of their component molecules at a speed greater than escape velocity. So you can heat the atmosphere evenly and while most or all of hydrogen can escape [over geological time periods] the fraction of the carbon dioxide that escapes over the same period will be much less.

So I was right all along when I said that the molecules' speed within a gas (doesn't just have to apply to an atmosphere) can reach and will go beyond the escape speed of the celestial body that the gas is on. I know that molecular mass (not 'weight', as terminology is important) also causes changes in the speed of molecules too, but I was trying to focus more on temperature.

 

[ZapperZ]

See, this is where it gets confusing, and why it seems that this topic is being approached differently by different people.

To me, the term "escape speed" means that the minimum speed needed for something to escape the gravitational field starting from the surface of the earth! But from what I'm seeing, it seems that this includes molecules escaping that are already in the upper atmosphere. Is that true? But is this what is defined as "escape speed" here? It certainly isn't how we defined it in standard classical mechanics.

If it is from the surface of the earth, then I will once again bring out the issue of the non-infinite mean-free path for such particles trying to escape.

Zz.

 

[russ_watters]

Oh, so basically what you are saying is that hotter gases will get less dense and will move faster towards space, right? If so, Ramon's question makes sense. But if you heat the whole atmosphere equally, nothing will happen but dilation.

No, it has nothing to do with density. It is about molecule speed relative to escape speed/velocity.

 

[russ_watters]

That's exactly what I was saying, that "if the speed is high, they can indeed escape" the celestial body that they are on. Therefore, with high enough temperature (combined with low molecular weight), a gas can reach and go beyond escape velocity, right? But what I'm not sure of is that if escape velocity can be reached by the increased speed of molecules (within the gas), which would lead the gas to escape from the planet.

That mostly sounds redundant (confirming your understanding), but it sounds like maybe you are unsure if the speed can really be high enough. The velocity distribution is along a bell curve (as jbriggs said), so even if the average speed is too low, a certain fraction will be high enough.

Wiki has a page discussing atmospheric escape:

http://en.m.wikipedia.org/wiki/Atmospheric_escape

 

[Remon]

See, this is where it gets confusing, and why it seems that this topic is being approached differently by different people.

To me, the term "escape speed" means that the minimum speed needed for something to escape the gravitational field starting from the surface of the earth! But from what I'm seeing, it seems that this includes molecules escaping that are already in the upper atmosphere. Is that true? But is this what is defined as "escape speed" here? It certainly isn't how we defined it in standard classical mechanics.

If it is from the surface of the earth, then I will once again bring out the issue of the non-infinite mean-free path for such particles trying to escape.

Zz.

So the difference between a gas escaping from the surface of the Earth and a gas escaping from the atmosphere (≈10 miles above Earth's surface) is that the escape velocity/speed is lower in the atmosphere? I know that's not what you said, but I'm assuming that that's main difference between directly "escaping" from the Earth's surface than from its atmosphere. And also, why do gas molecules have less "free space" to move on the surface of Earth than in its atmosphere? Wouldn't a particular gas (say CO₂) have the same amount of "free space" between each of its molecules on the surface of Earth as the atmosphere of earth? or does pressure play a role here (since there is less pressure in the atmosphere to "push" the molecules together)? I hope that made sense

 

[Integral]

I prefer "escape speed" because "escape velocity" wrongly implies that direction matters.

But it does. IF your velocity is directed toward the surface of the earth, you will not escape the atmosphere.

 

[russ_watters]

See, this is where it gets confusing, and why it seems that this topic is being approached differently by different people.

To me, the term "escape speed" means that the minimum speed needed for something to escape the gravitational field starting from the surface of the earth! But from what I'm seeing, it seems that this includes molecules escaping that are already in the upper atmosphere. Is that true? But is this what is defined as "escape speed" here? It certainly isn't how we defined it in standard classical mechanics.

Your interpretation is correct, but your definition is not: The surface of the Earth is a common reference point, but not the only useful one and it is not part of the definition. You can calculate it from anywhere.

http://en.m.wikipedia.org/wiki/Escape_velocity

 

[russ_watters]

But it does. IF your velocity is directed toward the surface of the earth, you will not escape the atmosphere.

True...

I know that's half in jest, but just to clarify: direction isn't part of the equation and the equation also treats the object like a point mass. We sometimes get questions about how direction affects escape speed, but the reality is that unless pointed at the ground or a building or another obstacle, it doesn't matter. You could, for example, tunnel through the center of the Earth and fire a projectile through it and the equation still works...

...but it probably fails if you start below the surface due to not accounting for the non-point size. Not sure though.

 

[Remon]

But it does. IF your velocity is directed toward the surface of the earth, you will not escape the atmosphere.

You don't say...
Anyways, this is kind of getting off topic (like most of my other threads... *sigh*) but I think I got my question answered... multiple times
In conclusion, a gas can escape from a celestial body (from the surface or from the atmosphere) with high enough temperature and low enough molecular mass (which is dependent on the gas), right? Which also explains why Titan has an atmosphere (because its cold, which leads to less movement between molecules, which "traps" the gasses on the moon)

 

[Integral]

This the reason we do not find the lighter gases, H and He specifically in our atmosphere. They are light enough that they can reach escape velocity at normal Earth temperatures. Escape, they do.

 

[Remon]

This the reason we do not find the lighter gases, H and He specifically in our atmosphere. They are light enough that they can reach escape velocity at normal Earth temperatures. Escape, they do.

... and escape, they did. Anyways, thank you guys for putting up with this somewhat long thread :)

 

[davenn]

... and escape, they did. Anyways, thank you guys for putting up with this somewhat long thread :)

No ... escape they DO as Integral said

present tense. Hydrogen ( and possibly Helium) is still being produce naturally and is still escapingDave

 

[Remon]

No ... escape they DO as Integral said

present tense. Hydrogen ( and possibly Helium) is still being produce naturally and is still escaping


Dave

Well, I am aware of the fact that there's probably a little bit of the lighter gases left in our atmosphere, I was just saying that most of these lighter gases have already escaped since the Earth was new

 

[HallsofIvy]

By the way, your original question was "If you apply enough heat to an object will it reach escape speed?" That is what the original posters were responding to. The idea that you were referring to individual molecules of a gas had to be postulated by others.

 

[Remon]

By the way, your original question was "If you apply enough heat to an object will it reach escape speed?" That is what the original posters were responding to. The idea that you were referring to individual molecules of a gas had to be postulated by others.

Well at first I said "object" but then I remembered that whatever object it is, its just going to turn into a gas anyways before ever reaching escape speed since it would normally go through the two other states before ever reaching escape speed, with gas obviously being the final state so I just switched from "object" to "gas"

 

[davenn]

Well at first I said "object" but then I remembered that whatever object it is, its just going to turn into a gas anyways before ever reaching escape speed since it would normally go through the two other states before ever reaching escape speed, with gas obviously being the final state so I just switched from "object" to "gas"

and can you see how this causes confusion, when people give answers based on your original question and then you suddenly change path mid way through the thread

This is why we ALWAYS encourage people asking questions to provide ALL the details up front and put that info into a good structured question(s)

Its helps us to give meaningful answers to the question poster

cheers
Dave

 

[anorlunda]

Think of molecules on the surface of as comet. Obviously, they reach escape velocity when warmed by the sun.

 

[the_emi_guy]

Lets keep in mind that temperature dictates *average* molecular speed. Some particles will be traveling many times faster than average at any frozen moment in time.