Science question

I googled,no luck.I am sure I am not using correct discription,therefore,I came here. A very long time ago while travelling with dad in an auto,at one place gas needed to be moved from our auto into another.I watched as one man after putting a rubber hose in our tank,sucked hard,gas came into his mouth which he then spit out and put the hose into a bucket where it flowed into. Being all of 5 years old,I damanded to know how the gas travelled up the pipe. I was told Nature abhors vaccum and as the man had sucked out the air gas rose to fill the vaccum. I was also told that there was a limit to how high liquid gas or water would rise to fill the vaccum. Folks, anyone know that height? Please help.

The heighth of the liquid in the original container once the vacum source is removed.

i don't think it's a vacuum's pull that makes a liquid rise up a tube, but the atmospheric pressure pushing on the liquid's surface that makes it raise to take the place of the vacuum and i think the height to which any liquid can be pushed through a tube is limited only by it's weight and if the atmospheric pressure can support.it.

so there is no fixed height answer for you, but at sea level the pressure there will get you to a height of around 34 feet according to this link :- http://water-chemistry.blogspot.com/2009/0…-weight-of.html

You are right it's the atmospheric pressure that will push the liquid up a tube. The greater the vacum the further it can be pushed. I was answering assumming the question was how high could you syphon a liquid.

it's the same thing really oldman.

The maximum height of the crest is limited by atmospheric pressure, the density of the liquid, and its vapour pressure. When the pressure within the liquid drops to below the liquid's vapor pressure, tiny vapor bubbles can begin to form at the high point and the siphon effect will end. This effect depends on how efficiently the liquid can nucleate bubbles; in the absence of impurities or rough surfaces to act as easy nucleation sites for bubbles, siphons can temporarily exceed their standard maximum height during the extended time it takes bubbles to nucleate. For water at standard atmospheric pressure, the maximum siphon height is approximately 10 m (32 feet); for mercury it is 76 cm (30 inches).

http://en.wikipedia.org/wiki/Siphon

personally with my lungs, i could probably syphon a max of 3 feet above source.

Have you ever used a Martian credit card? What's the simplest way to turn the gas pump off when using such a card?

nope, no idea what one is either, to stop the flow of fuel from a gas pump over here we just stop pressing then lever.. but your question did make me understand where you are coming from.. your talking about the flow will stop when the end of the pipe is raised to/above the level of the source, so therefore the max height you can siphon is below source level, correct? .

Yes. We were talking about the same thing I think but from slightly different angles. BTW the credit card is made of rubber, round in shape 1/2" diameter and about 4' long.

is it called that because everyone assumes martians always get their fuel by syphoning other peoples?

I've done a lot of syphoning in my time. Generally, from one of my vehicles to another. Really came in handy a few times when two or more jeeps were out in 4-wheel territory. I hate those flow-restriction valve balls they install now. But I do appreciate the need and purpose of installing them.

How's that? It wasn't meant to be offensive to anyone, just the name that it's always be called amonst a few others.

Generally, from one of my vehicles to another.

Generally?


@terry,

I don't know if that was the reason or not the term was coined. It may have started out as derogatory or may have been just some smarta.. but I think today it could fall under the heading of "colorful" slang. It probably started in the late 50's in the southwest. If you move a little farther east the credit card is known as a boardering state credit card. This whole post may border on being unPC but to give you an example of how some terms evolved from being totaly derogatory to acceptable I give you "Yankees" .


@wesi,

Apolgies for hijacking your thread. I hope somewhere in what terry1966 and I posted is the answer you are looking for.

I studied chemistry at college 30 years ago, before taking a completely different career path. But now it looks like my chemistry studies have finally come in useful for something.

As mentioned above, "The maximum height of the crest is limited by atmospheric pressure, the density of the liquid, and its vapour pressure." But, when you're dealing with volatile liquids like gasoline, temperature can have a significant effect as well. So, for this example, I will use a standard temperature of 25 C (77 F).

The maximum height of the crest is reached when the weight of the column of liquid becomes equal to the atmospheric pressure. It can be calculated by using this equation:

Maximum height of the crest = Atmospheric Pressure ÷ (The specific gravity of the fluid x The Gravitational Constant)

At 25 C, this works out at about 10 metres for water, and about 0.76 metres for Mercury.

At 25 C the specific gravity of water is is approximately 1.00.
At 25 C the specific gravity of gasoline is approximately 0.75.

So, because gasoline only weighs three quarters as much as water, theoretically the maximum crest would be higher. For water it is about 10 metres, so for gasoline it would be (1÷ 0.75) x 10 = about 13.3 metres.

But now you also have to take vapour pressure into account.

At 25 C the vapour pressure of water is approximately 3.2 kPa
At 25 C the vapour pressure of gasoline is approximately 6.5 kPa.

As you can see, at 25 C, the vapour pressure of gasoline is approximately double the vapour pressure of water.

When the pressure within the liquid drops to below the liquid's vapour pressure, vapour bubbles will form at the high point and the maximum height of the crest will be reached. So, because the vapour pressure of gasoline is approximately double the vapour pressure of water, the vapour bubbles will form at approximately half the pressure that it takes to cause vapour bubbles to form in water.

This means that you would only reach approximately half of the theoretical maximum crest height.

13.3 ÷ 2 = 6.65

So, at 25 C, the maximum crest height for gasoline would be about 6.65 metres.

(If that was Tomk's Monday Madness puzzle, I would have got a cookie for that. )

LOL. I don't know my doubles from my halves.

Where is says this above:

When the pressure within the liquid drops to below the liquid's vapour pressure, vapour bubbles will form at the high point and the maximum height of the crest will be reached. So, because the vapour pressure of gasoline is approximately double the vapour pressure of water, the vapour bubbles will form at approximately half the pressure that it takes to cause vapour bubbles to form in water.

It should say this:

When the pressure within the liquid drops to below the liquid's vapour pressure, vapour bubbles will form at the high point and the maximum height of the crest will be reached. So, because the vapour pressure of gasoline is approximately double the vapour pressure of water, the vapour bubbles will form at approximately double the pressure that it takes to cause vapour bubbles to form in water.

That was just me making a mess of my explanation. The answer is still the same, approximately 6.65 metres.

great explanation Achamian, and you get the cookie anyway.