# Water in upside down cup

Lock,In summary, if you turn upside down a cup of water on the top of a big container of water, then the water escapes out the cup and it becomes empty. If the cup has water in it and is lifted upside down in say a pan of water, as long as the cup doesn't break the field of the pan water and let in air, it keeps the water at the highest level of the cup because of the vacuum, that's what was meant. However, if the cup length is small enough, there won't be approximately any pressure difference.

In grade school I remember the physics experiment of the cup of water turned upside down on a card, and kept the water in the cup, my question is based on the same principle except that the cup is turned upside down in a bigger container of water, my question is , is the water in the cup at the same pressure as in the bigger container of water, or is it slightly different?
If it is slightly different , is the pressure in the cup any different from the top of the cup compared to the bottom of the cup?
Also if anyone knows a good link on this , I'd appreciate a heads up, Thanks

If the pressures were the same then there would be no net pressure force on the water in the glass and the force of gravity would be "unchallenged."

Water pressure grows from the surface to the bottom.

In grade school I remember the physics experiment of the cup of water turned upside down on a card, and kept the water in the cup, my question is based on the same principle except that the cup is turned upside down in a bigger container of water, my question is , is the water in the cup at the same pressure as in the bigger container of water, or is it slightly different?
If it is slightly different , is the pressure in the cup any different from the top of the cup compared to the bottom of the cup?
Also if anyone knows a good link on this , I'd appreciate a heads up, Thanks

Well, if you turn upside down a cup of water on the top of a big container of water, then the water escapes out the cup and it becomes empty. Am I loosing something?.

When the cup has water in it and is lifted upside down in say a pan of water, as long as the cup doesn't break the field of the pan water and let in air, it keeps the water at the highest level of the cup because of the vacuum, that's what was meant.

When the cup has water in it and is lifted upside down in say a pan of water, as long as the cup doesn't break the field of the pan water and let in air, it keeps the water at the highest level of the cup because of the vacuum, that's what was meant.

I see. Employ Hidrostatics. If the cup length is small enough, there won't be approximately any pressure difference.

Tide says, If the pressures were the same then there would be no net pressure force on the water in the glass and the force of gravity would be "unchallenged."
But wouldn't it be held in the glass by vacuum and not pressure, thus elimiting the build up of pressure?

Lock,

The air pressure inside the glass is not zero so it has to exert a downward force on the water. Likewise, the air below exerts an upward force on the water. The net pressure force is the sum of those forces (one negative and the other positive) and must be nonzero in order to sustain the weight of the water.

Tide said:
Lock,

The air pressure inside the glass is not zero so it has to exert a downward force on the water. Likewise, the air below exerts an upward force on the water. The net pressure force is the sum of those forces (one negative and the other positive) and must be nonzero in order to sustain the weight of the water.

the problem is air pressure not water pressure. as long as air cannot get in, the pressure inside will not change.

Tide is referring to the pressure at the water surface
just under the glass "bottom" (which is now on top) as "air pressure".
You "always" get a small amount of air inside the glass.

The pressure at higher elevations is always less than at lower,
unless there are drastic changes in the speed (here, vtop=vbottom=0)

## What causes water to stay in an upside down cup?

When a cup is placed upside down on a surface, the air pressure outside the cup is greater than the air pressure inside. This creates a vacuum, which prevents the water from escaping the cup and causes it to stay in place.

## Why does water stay in an upside down cup even when the cup is moved?

The vacuum created by the difference in air pressure remains until it is disrupted. Moving the cup quickly or at an angle can temporarily disrupt the vacuum, but it will reform and keep the water in the cup.

## Can any liquid be used in an upside down cup experiment?

No, not all liquids will behave the same way in this experiment. Water is a unique molecule with strong cohesive forces, which allows it to maintain its shape and form surface tension. Other liquids with different properties may not be able to form a strong enough vacuum to hold them in place.

## Can the amount of water in the cup affect the experiment?

Yes, the amount of water in the cup can affect the strength of the vacuum created. If there is too little water, the vacuum may not be strong enough to hold the water in place. Similarly, if there is too much water, the weight of the water may break the vacuum and cause it to spill out of the cup.

## Is there any practical application for this upside down cup experiment?

While this experiment may seem like a simple science demonstration, it has practical applications in industries such as aerospace and engineering. The concept of air pressure and vacuums is essential in designing and testing equipment that needs to function in different atmospheric conditions.