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Charles Link said:You need to write ## dW=(P_2-P_1)A \,dr=S \, dA' ##, where ## A=(2 \pi r) \, L ## and ## A'=2 \, ( 2 \pi r) \, L ##. Does that seem logical? ## \\ ##
Chestermiller said:If you slit the cylinder in half lengthwise and do a force balance on one of the halves, you have the following:
Pressure force on the half cylinder = ##\Delta P (2RL)##
Surface force on the half cylinder = ##4SL##
## A ## is the surface area of the sphere or cylinder. ## A' ## is the surface area that forms the surface tension. For a spherical droplet ## A =A' ##, but for a soap bubble with two surfaces,(inside and outside), and also for this cylindrical bubble that has two surfaces, ## A'=2 A ##.Jahnavi said:What is A' and dA' ?
Yes.Jahnavi said:In the expression for dW , A would be the outer surface area of the bubble , the one that is exposed to atmospheric pressure . Right ?
They were just trying to try to avoid the effects of putting end faces on it. It really doesn't need to be long. It can be a cylindrical bubble contained between two metal discs as @haruspex points out above. I agree with his input that otherwise, a cylindrical bubble is very hypothetical and simply does not occur in the real world. In many ways, these equations could be describing a cylindrical (elongated) balloon though, so it can be worthwhile to perform the computation as it may have other real world applications. (The tension in a balloon will increase with increasing dimensions, so I am only making a loose comparison here).Jahnavi said:Why do you think the cylinder has to be "very long " ?
Charles Link said:They were just trying to try to avoid the effects of putting end faces on it. It really doesn't need to be long. It can be a cylindrical bubble contained between two metal discs as @haruspex points out above. I agree with his input that otherwise, a cylindrical bubble is very hypothetical and simply does not occur in the real world. In many ways, these equations could be describing a cylindrical (elongated) balloon though, so it can be worthwhile to perform the computation as it may have other real world applications. (The tension in a balloon will increase with increasing dimensions, so I am only making a loose comparison here).
The excess pressure inside a soap bubble is caused by the surface tension of the soapy water. Surface tension is the force that holds the molecules of a liquid together, creating a "skin" on the surface of the liquid. In the case of soap bubbles, the surface tension of the soapy water is stronger than the pressure inside the bubble, causing it to stretch and create excess pressure.
The size of a soap bubble directly affects the excess pressure inside. The smaller the bubble, the greater the pressure. This is because the surface tension remains constant, but as the bubble gets smaller, the surface area decreases, causing the pressure to increase in order to maintain the bubble's shape.
Yes, changes in temperature can affect the excess pressure inside a soap bubble. A change in temperature can cause the molecules in the soapy water to either move faster or slower, altering the surface tension and therefore the excess pressure inside the bubble.
Soap bubbles eventually burst due to a decrease in excess pressure. As the bubble continues to stretch, the surface tension weakens, and the excess pressure decreases. Once the excess pressure is no longer strong enough to support the bubble's shape, it will burst.
No, the excess pressure inside a soap bubble is not always the same. It can vary depending on factors such as the size of the bubble, the concentration of soap in the water, and changes in temperature. However, the excess pressure will always be present as long as the bubble maintains its shape.