Why does the water defy gravity when you pour it?



The thing that it does sometimes when you poor water from a cup and some of it it just kind of sticks to the outside of it. It makes a mess and I never know how to prevent it.

In: Physics

It doesn’t defy gravity any more than a piece of tape stuck to the ceiling does. The water is simply “sticking” to the cup.

Water has a rather special property called surface tension. This is because water wants to stick together so it doesn’t defy gravity but rather the downward forces of gravity is equal or less than the “pulling” force of waters surface tensions (through something called Van der Waals force).

The surface tension holding the water to the glass is stronger than the gravity pulling it down.

Water molecules are made up of 1 Oxygen atom and 2 Hydrogen atoms. When these atoms come together to make water they make a triangle-like shape. Oxygen sits in the middle of the triangle. The two Hydrogen atoms are on two of the points of the triangle. The third point is where the extra outer electrons of Oxygen are; these are the electrons that are not being shared with the 2 Hydrogens in the outer layer.

When in this shape, the two Hydrogen atoms make that side of the triangle more positively charged and the electrons sitting at the opposite point make that side more negatively charged. Because of this special shape, water molecules like to stick together with each other and other charged things, like the side of a glass.

So when you pour water out of a glass slowly some water has a chance to stick to the glass. Eventually there is so much water that it weighs too much for that little charge to hold and the water falls off the glass.

This is only part of the reason this happens. Another part of the reason is a special way fluids can move called laminar flow.