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| Applications of Archimedes' Principle |
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 A floating ship displaces water equal to its own weight, including that of cargo. |
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| A submarine sinks by taking water into its buoyancy tanks. Once submerged, the upthrust is unchanged, but the weight of the submarine increases with the inflow of water and it sinks faster. Compressed air is used to blow water out of the tanks when it has to resurface. |
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| (An atomic submarine. This remains underwater for weeks without surfacing). |
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 Balloons filled with hot air or hydrogen, weigh less than weight of cold air that it displaces. Therefore, the upthrust is greater than its weight and the resultant upward force on the balloon, causes it to rise. |
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 Hydrometer is used to measure relative density of a liquid. It consists of a weighted sealed glass tube and a scale and when placed in the liquid, the scale reads the level of the liquid surface. In a denser liquid, the scale floats since less liquid is displaced. The weight of the displaced liquid is equal to its own weight, the number on the scale therefore, increases downwards. This method is use to check the state of a car battery. In a fully charged medium, the R.D of the acid should be 1.25 and recharging is required when reading is less than 1.8. |
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 Pressure is a scalar quantity, because its direction is unique (normal to the area) and not to be specified. |
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 Barometer uses mercury. This is because, if water were used, then a longer glass tube would have to be used (10m, since10m of water column is required to balance the atmospheric pressure.). Also water sticks to the glass tube. |
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 Blood pressure is measured in mm of Hg. The systolic pressure is 120mm of Hg and the diastolic pressure is 80mm of Hg. |
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 The thrust on the total area of the body of a man of a medium built (1.5m2) is 1.5 ton weight. How is he able to withstand this thrust? This is because there is a large number of opening and pores in the skin, through which air enters the system and presence of air inside, counterbalances the pressure outside. |
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 Pressure outside the human body changes at high altitudes or undersea. Therefore, precautions are to be taken to compensate for these differences. |
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