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Thrust and Pressure - Why Objects Float Or Sink When Placed on the Surface of Water?

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Why objects float or sink when placed on the surface of water?

  • Take a beaker filled with water 
  • take a piece of cork and iron nail of equal mass.
  • Place them on the surface of water.

Observation: The cork floats while the nail sinks. This happens because of the difference in their densities

The density of a substance is defined as the mass per unit volume. The density of cork is less than the density of water. This means that the upthrust of water on the cork is greater than the weight of the cork. So it floats.
The density of an iron nail is more than the density of water. This means that the upthrust of water on the iron nail is less than the weight of the nail. So it sinks. Therefore objects of density less than that of a liquid float on the liquid. The objects of density greater than that of a liquid sink in the liquid.

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