Okay, let's say I'm holding a wooden block. I then raise it above my head, then lower it to it's original position. Neither the kinetic or gravitational potential energy of the block has changed, so I have done no work on the block. However, I expended chemical energy to perform this action. Where does that energy go? Into the block? For example, if I shook a bottle of water up and down really fast then brought it back to its original position, the water will still be moving around, so wouldn't I have done work on it because I've put kinetic energy into the water in the bottle? Would I have done less work if I raised it and lowered it slowly, causing little movement in the water? Or is the water example fundamentally different from the block example?