Can materials with different surface properties move without external forces?

[mcjosep]

Ok, let's say you have a short cylinder (about a quarter inch tall and a three inch diameter) now take that cylinder and make one half of the circle hydrophilic and the other half hydrophobic (not the top one way and the bottom the other, I am talking about half the circle like how you would cut a pie), so one side attracts water while the other side repels it.

Shouldn't this cause the object to essentially surf the water without external force being applied? I know that there is an explanation as to why it won't move i just do not know what it is, and this scenario baffles me.

I'd imagine this would be an easy experiment to set up but I don't want to take the time right now to try and find an object that is hydrophilic and another that is hydrophobic in my kitchen cut them up and glue them together right now to test it.

thank you for your time.

 

[dav2008]

The object is just going to orient itself into a state that minimizes energy.

Think of it like two magnets. If you put two magnets close to each other, they will begin to move towards each other without any external forces in such a way that the South on one is oriented towards the North on another (well, each magnet individually feels an external force but it's internal to the two magnet system) . Once they hit each other, they can't come any closer so the motion stops. This is the state at which their potential energy is minimized so that's the state towards which they will naturally go.

Same with the cylinder. If you put it in the water a certain way, I assume the cylinder will orient itself in such a way as to minimize the amount of water on the hydrophobic side and maximize the amount of water on the hydrophilic side (of course you have to consider friction, buoyancy, gravity, etc) . Once it's reached that orientation, there's no reason for it to move any more.