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Some Important Formulae, F, P =, A, Force, Pressure (or Thrust), Area, Apparent weight of an object, = Weight of the object – Buoyant force, W., = W., - B, app, true, Apparent loss in weight of a, solid when inmmersed in water, Weight of water, [displaced by the solid, - W, = W, water, W., air, displaced water, Weight of solid in air, Weight of solid in air – Weight of solid in water, Wair, Relative density of a solid, d, d =, Wair - Wwater, 1

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Thrust and Pressure, What is meant by thrust, by, You have learnt about the force in the previous sections. Force can bo, applied on a surface in any direction., The force acting on any surface in a direction perpendicular (or, normal) to the surface is called thrust. Thrust is a vector quantity, • When a body is placed on a horizontal surface, it exerts a thrust equal, to its weight on the surface., ·A body resting on a horizontal surface will exert the same thrust, irrespective of its orientation., W, Force acts perpendicular, to the surface of the object, Force acts perpendicular, to the wall, Weight (m g), Weight (m g), 2

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Unit of thrust – The unit of thrust is the same as that of force. Thus,, the SI unit of thrust is newton (N)., In common use, thrust is also expressed in the unit of gram-force (gf), or kilogram-force (kgf)., 1 kgf = 9.8 N, 3

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(1 N = 100 gram-force), Other units of pressure are:, bar, 1 bar = 105 Nm-² = 105 Pa, atmospheric pressure, 1 atm = 1.02325 x 105 Nm-2, 1 atm = 1.02325 bar, 1 Nm-2 = 10 dyne cm-2, 4

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Force per unit area of the surface acting in a direction perpendicular, (or normal) to it is called pressure (P). If F is the force acting perpendicularly, on a surface having an area A, then, Force acting normally on the surface, F, or P =, A, Thrust, Pressure =, Area of the surface, Area, Pressure is a scalar quantity., • Units of pressure, square, (N m-²). Another name for the SI unit of pressure is pascal, (Ра)., The SI unit of pressure is newton per metre, 1 Pa = 1N m-2