Why do people say "Gravity does not suck, it pulls"?

What is sucking? When you suck, you lower the static pressure at one end of a volume, so that by Bernoullis law, the drop in static pressure results in a increased dynamic pressure - a liquid or gas is now flowing towards the lower static pressure. Sucking only works when you have total pressure available. If you have a vacuum around you (zero static pressure), sucking is impossible.

In your example, you don't pull the water directly, but bring it into your mouth by lowering the pressure on one end of the water, so that actually, the ambient air pressure, pushing on the water inside the glass, forces the water into the straw and towards your mouth.

Pulling is just exerting a force on an object which acts in the direction of the object that exerts the force.

Sucking is thus not the same as pulling.

To be more precise you actually apply a pull on the cross section of air next to you tongue and since that cross section of air want's to hold back by action reaction principle, it will apply a pull to the cross section of air next to it and so long and so forward until it reaches the water and same applies... Although since air isn't a solid thing but more like a compressible fluid, the model is slightly more complex but the fundamentals remain the same. Hopefully that was clear enough!!

EDIT: Apparently I haven't made myself clear enough... Gravity is a force that pulls. Now for most of you guys you know forces in the classical picture which is concept that's a little counter-intuitive. By that I mean that a force is "something" that pulls or repel two bodies and doesn't need a medium to communicate the motion of one of the two bodies with respect to the other. This said, you don't need a string or anything to apply a pull on something. A neat example for this is that of a magnet pulling a piece of metal. Also my first paragraph basically explains how sucking is basically pulling on the cross section right next to where you are sucking... Finally, if you want to know more about the non-classical picture of force, I strongly encourage you to have a look at the Standard Model on Wikipedia...

Cheers!

That's where you are wrong my friend.

A pull is a force that acts in the direction of the origin of the force

To suck is to draw (water, moisture, air, etc.) by or as if by suction

so as you can see gravity pulls, it doesn't suck

Simple solution. It all depends on the reference point of the observer.

Gravity is a force that acts from above the surface of a planet towards the core of that planet. Because we are on the surface of the planet, our reference point is the earth's surface. Gravity is pulling us away from the surface (towards the center of the earth). If we were at the core of the earth, our reference point is the earth's core. Then gravity is sucking towards us (from the surface of the earth).

scary stuff, gravity.

action at a distance. How EXACTLY does that work?

you say "pull"... well, don't you need a medium, like a rope, to act on an object... if no rope, what is left? The "Force"?

In this case, the force is Gravity, and Einstein said it dont need no stinking medium... its medium is SPACE, which it deforms... okay, so how does EM work?

action at a distance... ew.

A pull is a scattered force in the Earth total axis.

A suction is limited to a cylinder. In your example, a straw.

When you vaccuum the carpet, is it right to say the vaccuum cleaner is "pulling" the dirt?

When you drink through a straw, is it right to say you are "pulling" the fluid?

When you win a game of tug of war, is it right to say you sucked the opposing team into defeat?

*EDIT*

After reading your additional details, I decided I need more information on both "sucking" and "gravity."

http://answers.yahoo.com/question/index?qid=200810...

I just posted that related question, in hopes that I can get a better understanding. Maybe it's something as simple as fine-tuning the definitions of "suck" and "pull."

It's a mutual attraction.