Would a syringe in space suck?

[Lensmonkey]

Depends on how desperate you are? ;) This is a question of the nature of vacuums.
Part 1- In the relatively pure vacuum of space, (for this case let's consider it pure please). Can volume of a closed chamber be increased or decreased without force? (other than the friction of materials, but for this purpose consider theoretical no friction) Pulling the plunger would create no pressure difference, so no suction, right, or in a close cylinder, no resistance to volume change right?
Part 2 - I am given to understand that you cannot pull a liquid. Displacement pumps i understand to work by using the pressure difference of atmospheric pressure (the weight of air), to push a liquid into an area of lesser pressure, (created by increasing the volume per unit of material) in this case pulling a plunger! Say i have a 100 foot syringe. this syringe has the needle end sealed. let's say there is a cubic inch of air at the end, (the plunger is perfect and has no friction and an impermeable seal, the syringe cylinder is infinitely strong, as is the plunger). When i pull back on the plunger, i require greater and greater force to move the plunger. Will that force plateu and then become effectively constant? - Do i have this right: at equilibrium the pressure = the force with which the molecules are colliding against the plunger/piston and is equal on inside and out. When the plunger is pulled back, the inside molecules are not providing equivalent pressure/collisions and i must provide the extra force. This force is = to lifting the weight of a column of air the thickness of the area of the plunger surface minus the pressure exerted by whatever is in the volume inside the cylinder. Since this will become increasingly negligible, will the force necessary to expand the volume apprach a constant?
If i start with nothing at all in the cylinder, will i be able to continue to increase the volume of the chamber with a Constant force of 14.7 pounds per square inch(i think that's standard atmospheric pressure) until i reach the end of my syringe tube, or will i need to continually increase the force, if so, why. Thanks!

 

[Nugatory]

In a perfect vacuum you can move the plunger back and forth as much as you like, and the only force opposing you will be the friction of the plunger against the barrel of the syringe.

The resistance you feel when you're in the Earth's atmosphere and you pull the plunger out is caused by the air pressure outside the syringe wanting to push the plunger back in. In a perfect vacuum, there's no air, no pressure, hence no force to push the plunger in. In fact, if there were any air inside the syringe, its pressure would force the plunger out - this doesn't happen on Earth because the atmospheric pressure outside balances the pressure from the air inside.

 

[Drakkith]

As you pulled the plunger back on your sealed 100ft syringe you would have to apply a greater and greater amount of force to keep going. If you were in space then it would not, as there would be no air pushing the plunger back in.

 

[mfb]

If i start with nothing at all in the cylinder, will i be able to continue to increase the volume of the chamber with a Constant force of 14.7 pounds per square inch(i think that's standard atmospheric pressure) until i reach the end of my syringe tube

Correct. The same happens if you try to pump water (which is at atmospheric pressure) to a height of >10m. During the first 10m of raised water level in the pump, the required force increases, afterwards you can try to "suck your vacuum away" as much as you want, nothing changes.

 

[PJC01]

I would like to clarify a few things before addressing your question. Firstly, a vacuum is defined as an area with no matter present. While space may be considered a vacuum, it is not a perfect vacuum as there are still some particles present.

Now, to answer your question, a syringe in space would not suck in the traditional sense. Sucking is a term used to describe the movement of a fluid from an area of higher pressure to an area of lower pressure. In space, there is no atmosphere or surrounding medium to create a pressure difference, so there would be no movement of fluids.

In terms of your hypothetical scenario of a syringe in space with a perfect plunger and seal, the force required to move the plunger would not plateau and become constant. This is because, as you correctly stated, the pressure inside the syringe is equal to the force of the molecules colliding against the plunger. As you pull back on the plunger, the pressure inside the syringe will decrease, but it will never reach zero as there are always some particles present in space. Therefore, the force required to move the plunger will continue to increase as you expand the volume of the syringe.

Additionally, the force required to expand the volume of the syringe would not be a constant 14.7 pounds per square inch. This is because the pressure inside the syringe is not solely dependent on the weight of the column of air above it, but also on the number of particles present in that volume. As you expand the volume, the number of particles will decrease, causing the pressure to also decrease.

In summary, a syringe in space would not work in the same way as it does on Earth due to the absence of a surrounding medium and the presence of particles in space. The force required to move the plunger would not plateau and become constant, and the pressure inside the syringe would not be a constant 14.7 pounds per square inch. I hope this helps clarify your question.