# Pressure: Doubts & Explanation - Why Liquid Falls

• kent davidge
In summary, the conversation explores the concept of siphoning in liquids and why it occurs. The theory behind siphoning is not related to atmospheric pressure but rather the weight and height of the liquid in the siphon. A siphon with a greater height will have more powerful flow, while one with equal levels on both sides will not work. The process of siphoning stops when the water levels are equal.
kent davidge
Hi, I wonder if what I think is in according to the theory in Why the liquid falls. Check out the image I've uploaded. (sorry my bad english)

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No, this is nothing to do with atmospheric pressure (the same thing will happen in a vacuum) and the liquid will continue to flow until the surface in each container is at the same level (ie the depth in the lower container is greater).

The reason liquid flows in a siphon is because the weight of the water in the left side of the hose outweighs the water in the right side.

Imagine, instead of water, you had a long piece of string in the hose. At the right end of the string there is one marble tied to the string, at the left end, there are TWO marbles tied, weighing twice as much. Discounting friction, the string and marbles will slide into the lower bucket.

yes, I know that. But why it happens? Is it not because the difference between the pressure in each container?

kent davidge said:
Is it not because the difference between the pressure in each container?
No. Either side (or both) could be a 5 gal pail or an ocean. It would make zero difference.

What would make a difference is the height. A siphon falling 50 feet will be very powerful. A siphon falling 6 inches will be very weak, because there's very little pressure differential. That's also why - when the water level on both sides is equal - the siphoning process stops completely.

kent davidge said:
yes, I know that. But why it happens?
?? It happens because of the weight of water in the pipe.

good DaveC. I was typing my comment when you did your post. (sorry my bad english). Thank you.

## 1. What is pressure?

Pressure is defined as the force applied per unit area of a surface. It is typically measured in units of pascals (Pa) or pounds per square inch (psi).

## 2. How does pressure affect liquid?

Pressure affects liquid by causing it to flow or move in a certain direction. This is because liquids are unable to resist pressure and will flow from areas of high pressure to low pressure.

## 3. Why does liquid fall from a container?

Liquid falls from a container due to the force of gravity. When there is no supporting surface below the container, the liquid will be pulled down by gravity and fall towards the ground.

## 4. How is pressure related to the height of liquid in a container?

The pressure at the bottom of a container is directly related to the height of the liquid in the container. The greater the height of the liquid, the greater the pressure at the bottom of the container.

## 5. Can pressure be exerted on gases as well?

Yes, pressure can also be exerted on gases. This is because gases also have molecules that can be compressed and their movement can be affected by pressure.

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