When moving a liquid using the siphoning method what is it that makes it flow?
In: Physics
Gravity.
Or if you want to get a bit more technical, the gravitational potential energy of the liquid in the lower part of the siphon is converted to kinetic energy, some of which is converted to elastic potential energy acting on the liquid in the upper part of the siphon and then converting back to kinetic energy over and over to eventually reach the upper reservoir.
Oh and if there’s an atmosphere pushing down on the upper reservoir that helps, too.
But yeah, it really comes down to the weight and stickiness of the liquid.
Siphons work because gravity pulls down on the water on both sides of the pipe but the low end of the pipe has more water so the pull is stronger. The water in the low end pulls The water in the high end up until it reaches the top and starts pulling more water behind it.
This relies on the fact that water is incompressible. If it wasn’t, the water on the downside could pull the other end up – it would just get stretched out (loose pressure). Air is easily compressed so if you get too much air in the pipe the air gets decompressed and the water can flow back in both directions.
Edit: as has been pointed out, it’s less about the incompressibility than it is about the pressure differential in the pipe. When siphoning a heavy liquid like water, you need a lot of lift to get it over the hump which doesn’t work as well if there’s an air bubble at the top of the pipe
Surface tension holds the fluid column together. Gravity pulls downward on the two halves of the fluid column. The longer fluid column half has more downward force on it so the fluid flows in that direction.
Edit, it looks like everyone else beat me to it!
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