|MadSci Network: Physics|
Bill you asked "why can water not be compressed"? Matter in all forms is composed of extremely small particles called molecules. In the gas state the space that the molecules of a gas occupy is less than 1% of the space the gas occupies. In a liquid the molecules occupy about 70% of the space occupied by the liquid. Particles of matter are in constant motion. In a solid,this motion is restricted to a very small space. In liquids the particles have a more random motion but are restricted to a kind of rolling over each other. In a gas,the particles are in contentious random straight line motion. The decreased volume and increased intermolecular interaction in liquids is the reason a liquid expands and contracts only very slightly. When pressure is applied to a confined liquid there is little space for the molecules to move, since the molecules are so close together to start with the force is transmitted through the liquid with minimal compaction or compression of the fluid.
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