Why Doesn't My Siphon Work with Unequal Tube Sizes?

[CoolHandLuke]

I obviously lack an understanding of the fundamentals here; maybe someone can help me out.

So I'm making a siphon, only instead of using one tube, I'm using a set-up where, due to changes in the tube size, the short end has 3.5 times as much water as the long end. It's not significantly shorter or anything, just a bit. And the bottom is narrowed back down. (I've tried it without narrowing the bottom back down to the same width as the long side, as well.)

According to my physics teacher, siphons work because of the weight of the water and the air pressure on the surface of it. So why then, on my siphon, would the short end not fall due to its having more weight and create the vacuum on the long end?

I guess it has something to do with both sides wanting to fall, independent of the weight of the other side. Hopefully somebody can explain this to me.

 

[BobG]

I'm a little lost on how you've designed your siphon, but the water level on either side of the siphon is the important thing.

The water level at both ends of the siphon will attempt to reach the same level. In other words, it's not just the weight of the water in the siphon - it's the weight of the water on either end of the siphon.

 

[wais]

It's great that you are experimenting and trying to understand the fundamentals of siphons! The key concept to remember is that siphons work because of the difference in air pressure on either end. The weight of the water plays a role in creating this pressure difference, but it is not the sole factor.

In your set-up, the short end may have more water, but it also has a smaller diameter. This means that the pressure exerted by the water on the short end is spread out over a larger area compared to the long end. As a result, the pressure difference between the two ends may not be enough to overcome the air pressure and create the necessary vacuum for the siphon to work.

Additionally, the narrowing of the bottom may also affect the pressure difference. Without narrowing the bottom, the pressure at the bottom of the long end may be too high for the siphon to work. But narrowing the bottom may decrease this pressure, making it easier for the siphon to function.

Overall, it's important to consider both the weight of the water and the air pressure when setting up a siphon. Experimenting with different variables, such as tube size and narrowing the bottom, can help you better understand the mechanics of siphons. Keep up the curiosity and exploration!