Why are liquid surfaces at constant pressure?

In summary, the conversation discusses finding the shape of the surface of water when spun at a constant angular speed. The textbook gives a hint that the surface would be a surface of constant pressure, but the individual does not fully understand why. The expert then clarifies that surface pressure is equal to atmospheric pressure and that viscosity does not affect this relationship.
  • #1
dEdt
288
2
This is probably a stupid question with a simple answer, but please bear with me.

Suppose we have a bucket of water that we begin to spin at a constant angular speed. My textbook asked to find the shape of the surface of water, with the hint that the surface would be a surface of constant pressure. I got the right answer, but I don't fully understand why the surface should all be at the same pressure. I thought it had to do with preventing water from flowing along the surface, but I don't think that's it because different points of the fluid could be at different pressures without fluid flowing between them.

Also, does this (surface liquid makes = surface of constant pressure) hold if viscosity is introduces?
 
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  • #2
Surface pressure is equal to the atmospheric pressure which is assumed constant. Isn't it?
 
  • #3
Ah of course, that makes sense. Thanks.
 

FAQ: Why are liquid surfaces at constant pressure?

1. Why do liquid surfaces remain at constant pressure?

Liquid surfaces remain at constant pressure because of the force of gravity acting on the liquid molecules. This force creates a pressure at the surface of the liquid, and as long as the external pressure remains constant, the surface will also remain at constant pressure.

2. How does surface tension affect the constant pressure of liquids?

Surface tension is the cohesive force that holds liquid molecules together at the surface. This force results in a strong, stable surface that resists any changes in pressure. As long as the surface tension remains constant, the pressure at the surface will also remain constant.

3. Can the constant pressure of liquid surfaces be affected by temperature?

Yes, temperature can affect the constant pressure of liquid surfaces. As temperature increases, the molecules in the liquid gain more energy and move faster, which can lead to an increase in pressure at the surface. This is why boiling water creates bubbles on the surface and increases the pressure at that point.

4. What factors can cause changes in the constant pressure of liquid surfaces?

Changes in external pressure, surface tension, and temperature can all cause changes in the constant pressure of liquid surfaces. Other factors such as the presence of impurities or the addition of other substances can also affect the pressure at the surface.

5. How is the constant pressure of liquid surfaces important in various scientific fields?

The constant pressure of liquid surfaces is important in many scientific fields, such as chemistry, physics, and engineering. It plays a crucial role in understanding the behavior of liquids and their interactions with other substances. For example, it is essential in studying the surface tension of liquids, the formation of bubbles, and the flow of liquids in various systems.

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