Thrust and pressure

Tanusri Gururaj, Academic content writer of Physics at Edumarz

Force perpendicular to the surface.

SI unit: Newton (N)

The perpendicular force per unit area.

P = Thrust/Area

SI unit: N m-2 or Pascal (Pa)

  • As the area increases, pressure decreases. 

Force of the same magnitude acting on a smaller area exerts more pressure as compared to the same force acting on a larger area.

  • Liquids also exert pressure on the walls and base of the container in which they are present. 

This pressure is transmitted in all directions without being diminished.

When an object is immersed in a fluid, it experiences an upward force.

The magnitude of this force depends on the density of the fluid in which the object is immersed.

  • Why does a cork float on water but the nail sinks?

The density (mass per unit volume) of a cork is less than that of water.

Hence the upthrust is greater than the weight of the cork and, the cork floats. 

A nail on the other hand has more density than that of water.

Hence the weight is greater than the upthrust and, the nail sinks. 

  • Object floats: Upthrust > Weight of the object (density of the object is less than liquid)

  • Object sinks: Upthrust < Weight of the object (density of the object is more than liquid)

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