How does capillary action not violate conservation of energy?

[peter.ell]

I know that the law of conservation of energy is not violated by either complete destructive interference or capillary action, but I'm curious then what happens to the energy and where it comes from in these cases, since I can't figure it out.

Consider the case of complete destructive interference by either anti-reflective coatings or active noise canceling headphones. In both cases, two waves interfere completely destructively so as to cancel each other out, and the energy is not simply redistributed to areas of constructive interference because there are none. So what happens to the energy?

And in the case of capillary action, where does the energy come from? Is it all just from the potential energy of the intermolecular forces? If so, than that would mean that water molecules at the top of a tree have less intermolecular forces than water at the bottom, but I doubt this. Plus, the fact that energy must not only bring the water up the tree, but the fact that this water now has gravitational potential energy means that the energy from the upward moving water must be equal to the energy required to move up the tree PLUS all the gravitational potential energy that it will be able to exert if it suddenly fell from the top. Where does all this come from?

Thank you. I know I'm not thinking about this correctly, so I appreciate you enlightening me.

 

[Drakkith]

Consider the case of complete destructive interference by either anti-reflective coatings or active noise canceling headphones. In both cases, two waves interfere completely destructively so as to cancel each other out, and the energy is not simply redistributed to areas of constructive interference because there are none. So what happens to the energy?

An equal amount of energy was put into both waves. Each expends its energy to cancel the other out.

And in the case of capillary action, where does the energy come from? Is it all just from the potential energy of the intermolecular forces? If so, than that would mean that water molecules at the top of a tree have less intermolecular forces than water at the bottom, but I doubt this. Plus, the fact that energy must not only bring the water up the tree, but the fact that this water now has gravitational potential energy means that the energy from the upward moving water must be equal to the energy required to move up the tree PLUS all the gravitational potential energy that it will be able to exert if it suddenly fell from the top. Where does all this come from?

It is all intermolecular forces like you said. If the diameter of the capillary is small enough, then the intermolecular force can override gravity for a while. Once it gets wide enough it no longer has the energy to hold all the water up against gravity, otherwise you would see water creeping up over the sides of large barrels and such. I think that also explains why a narrow tube will only have a meniscus of a certain height. The combined weight of all the water eventually adds up and equals the capillary action, resulting in a stable meniscus.

If so, than that would mean that water molecules at the top of a tree have less intermolecular forces than water at the bottom, but I doubt this.

Why is that? The intermolecular forces are the same strength no matter where the water is.

 

[Dale]

Consider the case of complete destructive interference by either anti-reflective coatings or active noise canceling headphones. In both cases, two waves interfere completely destructively so as to cancel each other out, and the energy is not simply redistributed to areas of constructive interference because there are none.

In the case of noise canceling headphones there are, in fact, areas of constructive interference. In addition, for both noise canceling headphones and anti-reflective coatings the remainder of the energy goes into heat.

 

[Bill_K]

Plus, the fact that energy must not only bring the water up the tree, but the fact that this water now has gravitational potential energy means that the energy from the upward moving water must be equal to the energy required to move up the tree PLUS all the gravitational potential energy that it will be able to exert if it suddenly fell from the top.

Didn't you just count the same energy twice?

 

[sophiecentaur]

In anti reflective coatings the energy all goes forward. There needs to be no loss. It's just like a lossless matching network at the interface between transmission lines of different impedances. Remember, it only works over a finite bandwidth.

In capillary action, presumably there is a reduction in temperature / internal energy? That would account for where the energy came from. With thermal energy, a little goes a long way when transferred to mechanical energy.

 

[Lsos]

What's stopping us from using capillary action to raise water and then use that water to turn a turbine?

I admit I don't know the answer, but I suspect the answer will help satisfactorily address OP's question.

 

[Dale]

How would you get the water out of the capillary in order to turn the turbine?

 

[Mapes]

What's stopping us from using capillary action to raise water and then use that water to turn a turbine?

Capillary action occurs when the surface energy of a dry surface is higher than the surface energy of a wet surface. The water moves to wet the surface because it decreases the total free energy. But it takes energy to remove that water and dry the surface again; the energy isn't free!