# Why is boiling water bubbling?

• rogerk8
In summary, Roger attempted to explain the bubbling phenomena in boiling water and found that it is due to a gas being less dense than a liquid. Surface tension tries to reduce the size of the bubbles, and convection happens to move the gas around.
sophiecentaur said:
.. . . and many others of your questions.
It seems to me that probably you need some more basic Physics if you are to go further. one can't run before walking.
There are many sources of info on the web but they will not all suit your particular level. I found this one which may help you. Try to read a lot of it before coming up with questions.

Thank you very much for that link.

Please correct me if I'm wrong but isn't the whole purpose of a forum to ask questions?

And cut some corners?

I have studied more than you might believe and I'm tired of theory!

I want to understand.

To understand my own way.

Not by reading a lot of formulas about everything which often actually teaches you nothing.

Nothing that makes you really understand, anyway.

So I'm using this nice forum to "blog" about my thinking.

Hope you don't mind

Roger
PS
Please do not take my questions too seriously. Sometimes I ask a question just to get it on the table while being only lightly insecure about the answer.

In any case, I refere to my signature.

Last edited:
sophiecentaur, I wish to add a link in my signature would you mind helping me?

I can't seem to find out how to do that.

Roger

I take back my former statement, your link seems to lack equations almost totally so it is just educational.

Thanks!

Roger

Last edited:
rogerk8 said:
I'm tired of theory!
As far as I am concern ed, "tired of theory" is the equivalent of "tired of Physics".
If, as you say, you want short cuts then you run a massive risk of getting such a limited view of the subject that you will get totally the wrong picture.
If you don't like equations then you are also limiting your potential understanding. Maths (and I have made this point so so many times on PF) is the language and If you don't want to use it, you just can't get it. Someone else on PF likened it to the process of trying to study French poetry without learning the French language.
rogerk8 said:
I wish to add a link in my signature would you mind helping me?
Sorry. I have no idea. You could try one of the computer based sections of PF.

Interesting.

You misunderstood me completelly.

I love equations, but reading litterature often gives you equations while you at the same time do not fully understand the basics behind them.

What I'm saying is that you need to have a kind of abstract understanding of the subject before you are being served equations.

Otherwise the equations just look nice.

Like the ideal gas law which I still do not understand.

But I'm beginnig to grasp the concept of (gas) pressure in the terms of J/m^3 with the thankful aid of Wikipedia who told me that a system under pressure has the potential to do work on its surroundings which means that pressure is a measure of potential energy stored in a unit volume.

I can relate to this but actually I do not understand this at all!

Roger

Today at gym it suddenly struck me that

$$P=\rho_s \frac{dv}{dt}...[N/m^2]$$

This while only thinking unit substitution in the familiar

$$F=m\frac{dv}{dt}...[N]$$

But this also makes me kind of begin to understand pressure which is my quest.

It tells me that gas pressure has to do with collective behaviour of a gas.

Because it has mass within a unit area (i.e surface density).

It seems like force isn't relevant within a gas and that it's counterpart is pressure.

This is obvious from the way I derived this.

But don't think I'm ready with my quest.

Far from it!

Let's view the acceleration part that is

$$a=\frac{dv}{dt}$$

How do we know it?

Imagening a particle of gas hitting the cannister wall.

If we for simplicity consider totally elastic collision.

The impulse change is then (normal angle)

$$\Delta p=2p$$

or with regard to speed, 2v due to same mass.

So we have a maximum speed change of 2v.

Okey, let's consither this and set

$$dv=2v$$

Now, during how long time did this speed change happen?

Because if we doesn't know that, we do not know what the pressure is.

Even though we might be able to calculate it knowing density and temperature, but that is cheating

So what limits the rate of speed change?

Because throwing a steel ball into a steel wall will give the same speed after as before but during what time span?

Wait a minute, wouldn't the steel ball just fall to the floor right next to the wall?

I understand nothing

Roger
PS
I should have said "I'm tired of reading" and not "I'm tired of theory", sorry.

Also, I think it is important to fully understand all the variables before any equation really makes sense.

Last edited:
If you take a column of water and throw that at a window at a certain speed, the window will shatter at a certain length of that column.

But if you take a column of gas and throw that at a window at the same speed, the window will shatter at a certain area of that column.

The first statement is due to liquid incompressibily which makes force a matter of column length.

The second statement is due to the gas being compressible and thus force is not dependent of column length but on the integration of surface density.

How far off am I now?

Roger

• Mechanics
Replies
13
Views
2K
• Mechanics
Replies
20
Views
32K
• Mechanics
Replies
13
Views
4K
• Classical Physics
Replies
11
Views
2K
• Mechanics
Replies
6
Views
3K
• Mechanics
Replies
9
Views
6K
• Mechanical Engineering
Replies
8
Views
1K
• Mechanics
Replies
5
Views
4K
• Mechanics
Replies
1
Views
1K
• Introductory Physics Homework Help
Replies
15
Views
216