does anyone in Y!A know the answer of this question?!?

Question

i've a question on air pressure. The question goes like this:
when the piston of a syringe is pull out the water get into the barrel, but what is the relationship between air pressure with this nasty question. I need help, my science teacher will be asking me about this question TOMMOROW!!

Answer 1

First of all, I would suggest that you copy the question verbatim (word for word) when you post on Yahoo. The words you wrote do not form a question.

I believe that you are trying to describe a situation where a syringe is used to draw up some water. Exerting force on the piston creates a negative air pressure inside the syringe so that water enters it.

This is described by Boyle's law.

Here's another way to think about it. With the piston closed there is very little volume in the syringe. What volume there is in the syringe exerts equal and opposite pressure on the water in the reservoir. Moving the piston increases the volume available to gasses and liquids inside of it. Since the temperature is held constant, increasing the volume decreases the pressure inside the syringe. Since the syringe has an open tip, this pressure is transmitted equally throughout the entire system (i.e. into the reservoir). For the moment the syringe is filling, there is a difference in pressure between the reservoir and syringe. Water from the reservoir must enter the syringe to keep the pressure of the system constant.

Answer 2

When you stick the end of a syringe into water and pull the plunger, you create a lower pressure inside the syringe than on top of the water. So the water is forced innto the cyringe cylinder by a combination of atmosperhic pressure pushing down on top of the, plus the weight of the water above the end of the syrinde.

Ordinarily you don't stick the syringe into the water very deep, so the pressure dut to the liquid level of the water is very small. Most of the pressure is due to the atmosphere - 14.7 psia.

Now if you had a very long syringe that for example you stuck into a lake. You would have 14.7 psia plus the pressure from the water. Water exerts a pressure of 1 psia for every 2.3 ft of depth.

So if you stuck the syringe in to a depth of 2 feet, it would 14.7 psia + 2x2.3psia that would be the pressure pushing water into the syringe.

Answer 3

it's simple.the normal atmospheric pressure is 76mm of mercury at sea level.
when u place a syringe in water and pull the piston of it upwards,then u reduce the air pressure inside the syringe.now the pressure outside the syringe i mean the pressure that the water exerts is more than the pressure inside the barrel.this causes the water to enter the barrel.

the reason why air pressure decreases is when u pull the piston up the air molecules inside the barrel become separated i mean they move wider apart,because u are increasing the space but at the same time u are not increasing the number of molecules in it ; the property of a gas is to occupy space in the barrel uniformly.this causes the molecules to move wider apart and creating a partial vacuum.once vacuum is created the pressure inside the barrel tends to fall and of course it falls.but the pressure outside i mean in the water is more than that of the pressure inside the barrel as i told u already,this causes an upward rise of water into the barrel

that's it.bye

Answer 4

When you pull back the plunger you create a vacuum which the liquid naturally fills. Sea level pressure at 32 degrees F is 14.7 lbs/sq. in. Since the water has a 600-mile-high column of air sitting on it and it suddenly has an area of virtually no pressure available to it that column of air presses the water into the syringe.

Answer 5

Air pressure is decreased as the plunger is pulled back which allows the water to enter the syringe.

Answer 6

hurm...i think it goes like this....
When you pull the syringe, the air pressure inside the syringe is lower than the air pressure on the outdie...therefore, water will enter the syringe...