[hamdani yusuf (OP)]

We answered that 11 pages ago/
Quote from: Bored chemist on 19/03/2022 11:45:18
Quote from: hamdani yusuf on 19/03/2022 03:56:58
The question is, what distinguishes thermal energy from kinetic energy?
The motion having some sort of structure, rather than being random. Essentially, it's an effect of entropy.

How would entropy relate total kinetic energy and temperature of an object? Is it simply a multiplication?
How can we get negative temperature?

Is there a magnitude of negative temperature? Can an object have more negative temperature than another object? What would happen if they interact?

[hamdani yusuf (OP)]

How is the temperature measured before reaching equilibrium?

Sometimes you can do this spectroscopically.
Sometimes it's impossible.

What are the criteria to make it possible?

[hamdani yusuf (OP)]

If you haven't got it sorted out after 12 pages of coaching, you probably never will.

Here's what I've got in second page.  How much further do I need to go?

Afaik, thermal energy has highest entropy among other kinds of energy, which makes it the most random form.

Black body radiation is the simplest spectral distribution of thermal electromagnetic radiation. The object's temperature can be calculated from the peak frequency. But most objects are not black body. Spectrum of low pressure gas has much different shape than black body radiation.

[Bored chemist]

How can we get negative temperature?

I answered this earlier.

https://en.wikipedia.org/wiki/Negative_temperature#Lasers

As I said, it seems you can't keep an idea in your head long enough to learn about this sort of thing.
Give up; you are just wasting everyone's time including your own.

[hamdani yusuf (OP)]

I answered this earlier.

If you think that you already understand something by simply pointing to an online article, which mentions it, you are likely being delusional.
If you really understand it, you should be able to answer these questions easily.

How is the temperature measured before reaching equilibrium?

Sometimes you can do this spectroscopically.
Sometimes it's impossible.

What are the criteria to make it possible?

[hamdani yusuf (OP)]

Is there a magnitude of negative temperature? Can an object have more negative temperature than another object? What would happen if they interact?

[Bored chemist]

I answered this earlier.

If you think that you already understand something by simply pointing to an online article, which mentions it, you are likely being delusional.
If you really understand it, you should be able to answer these questions easily.

How is the temperature measured before reaching equilibrium?

Sometimes you can do this spectroscopically.
Sometimes it's impossible.

What are the criteria to make it possible?

You have repeatedly demonstrated that you don't even understand the easy stuff.
Why waste everyone's time with the more sophisticated bits?

[hamdani yusuf (OP)]

You have repeatedly demonstrated that you don't even understand the easy stuff.
Why waste everyone's time with the more sophisticated bits?

It's okay to say that you don't know. Pretending to know something that you don't know is not a scientific attitude.

[Bored chemist]

You have repeatedly demonstrated that you don't even understand the easy stuff.
Why waste everyone's time with the more sophisticated bits?

It's okay to say that you don't know. Pretending to know something that you don't know is not a scientific attitude.

What you said is true.
However, it's unconnected to what you quoted me as saying.
Why did you quote me?

[hamdani yusuf (OP)]

What you said is true.
However, it's unconnected to what you quoted me as saying.
Why did you quote me?

Your comments seem to imply that you already understand something that I don't. But so far, you failed to answer some simple questions, like these.

Is there a magnitude of negative temperature? Can an object have more negative temperature than another object? What would happen if they interact?

[hamdani yusuf (OP)]

How do we know the temperature of the cube?

[hamdani yusuf (OP)]

Talking about heat shield, you might find this video quite informative. 

[Bored chemist]

But so far, you failed to answer some simple questions, like these.

The questions are simple. the answers are not.
And, since you don't understand the simple stuff, you will not understand the complicated stuff.
Why would I bother posting a reply that you will never comprehend?

[Bored chemist]

How do we know the temperature of the cube?

It obviously does not have one.
Bits are clearly much hotter than others.
Something like a thermal camera could give us an indication of the temperature distribution.

This is the sort of thing I mean when I say

you don't understand the simple stuff

[hamdani yusuf (OP)]

And here's a discussion about temperature.

[Bored chemist]

Talking about heat shield, you might find this video quite informative.

Yes. I discovered that they still talk about "friction" causing heating even though that's a minor part of the cause. Most is due to near adiabatic compression.

Also, they are wrong about another aspect.
He complains that a guy in a film falls from a spacecraft + burns up.
He says that's nonsense because the vehicle is moving along with the planet.

But he misses the point.
If you fall, you accelerate.
If you start from a spaceship, you aren't slowed down by the air (there isn't any).
So you end up going very fast indeed- well over the speed of sound.
And then you hit the air.
That air slows you down to terminal velocity and as it does so, the air ahead of you is compressed forming a shockwave. That heats it.
And that very hot air, just in front of you heats you up
Essentially, it's the same thing that he does talk about. As you hit the air, you have lots of energy (gravitational rather than kinetic). That energy has to be dissipated somehow (or you will crash).
And the only realistic fate for that energy is to be converted to heat.

That's what burns you up.

The effect was noticeable when Felix Baumgartner jumped from a balloon.

There's another point he glosses over.
Retrorockets have to point forwards.
That means you end up flying into the output from your rocket.
It's not a big deal in space because the gas is going much faster than you are so you never "hit" it.

But if you fire a retrorocket into air the hot exhaust gasses are slowed down a lot.
And that means you end up flying into the rocket exhaust.

You need roughly the same amount of heat shielding to address that problem as you do to shield you from the heat created by aerobraking.

He's sort of right. the very front surface of the blunt end of a re-entry vehicle is an aerobrake.
But you could make that from a sheet of metal. It doesn't need to be very strong (in the context of the vehicle weight, for example). The forces on it are , in principle, in simple compression. And, since the acceleration caused by the brakes is only of the order of a few G (1.7 G for the space shuttle, for example), the forces are only of the order of a few times the weight.

If it was't a heat shield, you could make it from 6mm aluminum sheet (properly braced) and it would probably be "over engineered".



But it does have to avoid being destroyed by the thermal radiation from the superheated air in front of it; and it also needs to protect the rest of the vehicle from that heat too.

So... it's a heat shield.

So, yes, I can learn a lot from that video but...

[hamdani yusuf (OP)]

But so far, you failed to answer some simple questions, like these.

The questions are simple. the answers are not.
And, since you don't understand the simple stuff, you will not understand the complicated stuff.
Why would I bother posting a reply that you will never comprehend?

The first two questions are just closed yes/no questions. You can answer them with yes or no. Or just say that you don't know.
The last question can be answered by saying if there will be energy transfer. If it is, the next required answer would be which way is the direction of the energy transfer.
If they are too complicated for you, I can't help but think that you don't really understand it.

[Bored chemist]

If the questions are as simple as you say, then you can answer them.

[Bored chemist]

Is there a magnitude of negative temperature?
Yes
That's clear from the article I cited; unfortunately, you don't understand it.
Can an object have more negative temperature than another object?
Yes; that's clear from the answer above.
What would happen if they interact?
What do you mean by "they"?

That's the sort of thing I mean when I say

Could you at least try to think about your questions a bit before you ask them?

[alancalverd]

James Joule settled the business of falling through the atmosphere of Venus in the 1840s, when he deduced the mechanical equivalent of heat from a number of remarkably precise experiments. Sadly, it seems that his famous "honeymoon experiment" to measure the temperature rise of water falling in a cascade at Chamonix, was beset by errors and unknowns, but a great deal of thermodynamics relies on his smaller investigations.