Sucking cranberry juice out of a hose

[member 392791]

I just watched the walter lewin lecture on fluids, and he had an experiment where he was sucking it out of a hose when the hose was in a U-shape, and he was only able to bring the level up about a meter. However, when he got on a ladder and was sucking out the juice from the floor in the container, there wasn't any trouble sucking it out 5 meters

Somehow him being on the ladder 5 meters up is the reason for this, and I can't figure out how this works.

For the 2nd experiment, he was sucking the air out of the hose creating a vacuum, so the air pressure at the bottom of the container was pushing the liquid up. But, I would think the same principle would apply for the one at ground level, yet it didnt.

 

[haruspex]

If I found the right video, he did not suck juice up a height of 5m. Nobody could.
He sucked the juice up a short way then closed the top of the tube and lifted it 5m.

 

[member 392791]

no he definitely was sucking the whole time...but I think it could be that the beaker had a much larger surface area than the tiny hole from the first experiment.

 

[haruspex]

Then please direct me to the right video and time from start.
The area shouldn't matter. If it's all the same airspace then it's all at the same pressure. No human can get lung pressure down to half an atmosphere - you'd be crushed.

 

[member 392791]

http://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/video-lectures/lecture-27/

at 48:30 is when it begins

 

[haruspex]

OK, I've got it. We assumed sucking is done with the lungs, but when a strong vacuum is required we naturally switch to a different technique. The sucking is done with the tongue, throat closed. (Check: you can still breathe when sucking hard.) The tongue is pretty strong. The tongue then closes the off the airway at the front of the mouth and opens up at the back, allowing the withdrawn air to be removed (but now at a higher pressure).