# The Naked Scientists Forum

### Author Topic: bubbles  (Read 4208 times)

#### mrfinger6

• First timers
• Posts: 3
##### bubbles
« on: 28/12/2005 00:14:14 »
Can you tell me the Quantum Mechanics of a bubble blown from kids toy bubbles?

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: bubbles
« Reply #1 on: 28/12/2005 23:16:49 »
Because of its size and construction a bubble's behaviour is adequately described by classical physics.  As the water drains to the bottom of the bubble the colours demonstrate the wavelength of light by thin film diffraction and quite interestingly dissappear as the top part of the bubble becomes invisible just before it bursts.

Had you any particular aspects of bubble behavour in mind when you asked this question?

Learn, create, test and tell
evolution rules in all things
God says so!

#### realmswalker

• Sr. Member
• Posts: 205
##### Re: bubbles
« Reply #2 on: 29/12/2005 03:57:37 »
www.zubbles.com

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: bubbles
« Reply #3 on: 29/12/2005 10:13:06 »
Interesting and fun

Learn, create, test and tell
evolution rules in all things
God says so!
« Last Edit: 29/12/2005 10:13:43 by Soul Surfer »

#### mrfinger6

• First timers
• Posts: 3
##### Re: bubbles
« Reply #4 on: 30/12/2005 00:13:45 »
Actually yes. Bare with me please as I am truly a super novice just getting interested into physics and things like quantum mechanics. I was thinking more along the lines of what makes a bubble round? What forces determine the size  and shape of the bubble? Is it outside forces acting on the bubble from every axis possible is that why it is round?

quote:
Originally posted by Soul Surfer

Because of its size and construction a bubble's behaviour is adequately described by classical physics.  As the water drains to the bottom of the bubble the colours demonstrate the wavelength of light by thin film diffraction and quite interestingly dissappear as the top part of the bubble becomes invisible just before it bursts.

Had you any particular aspects of bubble behavour in mind when you asked this question?

Learn, create, test and tell
evolution rules in all things
God says so!

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: bubbles
« Reply #5 on: 30/12/2005 11:01:47 »
Bubbles are the result of surface tension in a liquid.  The atoms or molecules in a liquid clearly have more attractive forces associated with them than a gas bcause the liquid manages to hold itself together when you put it in a container.  Throughout the body of the liquid as the molecules jostle together these attractive forces are balanced and the liquid can move about but at the surface these forces are not balanced and so the molecules at the surface are held down more strongly.  This excess of force is called surface tension and it is strongly dependant on the structure of the surface. Nomally water bubbles do not last very long because the water drains down and the bubble pops but if you add detergents a big change takes place.

Now you know that oil and water don't mix the just form blobs in each other and some substances like salt dissolve in water and some substances like wax dissolve in oil.  So if you make a molecule that likes water at one end and oil at the other it will help the oil and water to mix by sitting on the surface of the water and oil (this is a detergent)  Detergernts or emulsifying agents can allow bubbles to form and last much longer than the would do in just water by effectively helping to hold the surface together and solwing down the way the water drains to the bottom of the bubble to allow the top to break and the bubble pop.

One of the important characteristics of this soap film is that it is always trying to contract (hence the name surface tension) and be as small as possible so, in the absence of any other influences, it will be spherical because a sphere is the shape that contains the largest amount of Volume possible inside the smallest area of surface.

One other important feature if a bubble is that there is always a slight pressure inside it.  This is caused by the curved film of water and detergent trying to contract.  The interesting fact about this is that the more curved the film ie the smaller the bubble the higher this pressure is so small bubbles are much stronger and more stiff than big ones.

Learn, create, test and tell
evolution rules in all things
God says so!
« Last Edit: 30/12/2005 11:16:41 by Soul Surfer »

#### ROBERT

• Guest
##### Re: bubbles
« Reply #6 on: 05/01/2006 18:23:23 »
Quote
Originally posted by Soul Surfer

Because of its size and construction a bubble's behaviour is adequately described by classical physics.  As the water drains to the bottom of the bubble the colours demonstrate the wavelength of light by thin film diffraction and quite interestingly dissappear as the top part of the bubble becomes invisible just before it bursts.

Hi Soul Surfer,
sorry for being pedantic but, the colours seen on soap film are produced by interference, NOT "diffraction".
You are correct about the "invisible" bit: the black "holes" in these soap films are where the film is thinnest.

« Last Edit: 10/01/2006 09:52:35 by ROBERT »

#### The Naked Scientists Forum

##### Re: bubbles
« Reply #6 on: 05/01/2006 18:23:23 »