When two solvents are seperated by a semi premamble membrane, water flows

Water flows from the side of higher water potential (higher water concentration leads to higher water potential) to the side of lower water potential. 

This movement is called osmosis. Water potential means the tendency of water flowing away. The higher the water concentration the solvent/solution is, the higher the water potential is and the more likely it'll flow to the other side. 

Therefore, if one of the solvents has 10% water and the other has 50% water, water molecules will flow from the one with 50% water to the 10% one. This movement is completely natural and does not require extra energy. The net flow will stop until both sides have the same water concentration. Water still flows through both sides at that time, but no net flow. 

Note that osmosis is only the movement of water molecules, with the presence of semi-permeable membrane (which can decide what substances can go through), and the flow of down the water potential gradient. If any one of these is not applicable, the movement is not osmosis. 

It's speed of rotation.

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