# Water potential

1. May 19, 2006

### chound

Is water potential the kinetic energy or potential energy of water? Coz my textbook says it potential energy whereas another reference book says ts kietic energy

2. May 19, 2006

Staff Emeritus
Excuse me, is this a technical term in biology? Because normally the word potential, used by itself, means potential energy. The potential energy DIFFERENCE between a particle of water at two different heights is the mass of the particle times the height difference. If the particle then FALLS from the heigher height to the lower one, the kinetic energy (energy of motion) that it has gained at the bottom of the fall will equal the potential energy that it has lost; $$\frac{1}{2}mv^2 = md$$.

3. May 29, 2006

### quantumcarl

How about the potential water offers for the development of life? Is there a physics formula for that?!?!

It must have to do with the bond and the simple molecular structure of the H20.

Another thing about water I've heard is that it mimics the configuration of any other chemical or solution that enters it. I was told this as an explaination for the mechanism of dissolution or dilution. This would present another potential water holds.... in the common use of the word "potential".

Potentially, water (under high pressure) can and is used as a laser to cut stone, wood and even metal. Probably an Egyptian invention .

Here's a page on "Standard metal cutting processes: laser cutting vs. water jet cutting"

http://www.teskolaser.com/waterjet_cutting.html

Last edited: May 29, 2006
4. May 30, 2006

### Hootenanny

Staff Emeritus
Water potential ($\Psi$) is used to describe the osmotic gradient, that fact that water will always move to an area of lower water potential. Water potential can be described in terms of Gibbs free energy;

$$\Psi = \frac{G}{V}$$

Where V is the molar volume of water. Water potential is a measure of the free energy in a solution. The lower the water potential the less free energy there is in the system the more potential energy there is. Therefore, water potential can be said to me a measure of potential energy.

~H

5. May 30, 2006

### Gokul43201

Staff Emeritus
"Water potential" is nothing but the chemical potential of water in any system where water is a component (eg: in a solution).

$$\mu_{water} = \left( \frac {\partial G}{\partial n_{water}} \right) _{S,V,n_{others}}$$

Naturally, since G, the Gibb's Free Energy (or U, H or F, which can also be used in a definition like the one above) is intensive, the "water potential" of pure water (or pure anything else) under standard conditions is 0.

The water potential (or any chemical potential) is not an energy at all, though in some cases it is looks like one. When it does, it seems to resemble a potential energy. This is not, however, to say that it is independent of the KE of particles in the system. It isn't, as is evident if you write the definition in terms of the Helmholtz Free Energy, F(T,V,{n}).

For an equeous solution, the water potential is given by (if you're not too picky about accuracy) the slope of the graph of standard enthalpy of dilution as a function of the mole fraction of water (though usually, the graph is drawn with respect to the mole fraction of the solute).

6. May 30, 2006

### Hootenanny

Staff Emeritus
I stand corrected.

~H

7. May 30, 2006

### quantumcarl

Yo! Heavy duty physics dudes!

Is there a similar equation for Sodium potential or Potassium potential... in reference to the sodium/potassium osmotic "pump" or the osmotic pressure created along a neuron's axon (resulting in em activity)?