# HIGHER PHYSICS

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HIGHER PHYSICS. Upthrust, Floating &amp; Sinking. Any object placed in a fluid receives an upward force, due to the pressure at that depth. F upthrust. h. F weight. surface area, A. liquid density, ρ. UPTHRUST. i.e. F = pA &amp; p = ρ gh So, F upthrust = ρ ghA. Resultant force on object,
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HIGHER PHYSICSUpthrust, Floating & SinkingAny object placed in a fluid receives an upward force, due to the pressure at that depth.FupthrusthFweightsurface area, Aliquid density, ρUPTHRUSTi.e. F = pA & p = ρgh So, Fupthrust = ρghAResultant force on object,Fresultant = Fweight - FupthrustExample – 1kg iron mass (see Virtual ‘H’ Physics)mass, m = 1 kg, Fweight = mg = 1 x 9.8 = 9.8 Narea of base, A = 0.0025 m2, depth, h = 2 cm = 0.02 mFupthrust = ρghA = 1000 x 9.8 x 0.02 x 0.0025 = 0.49 NFresultant = Fweight – Fupthrust = 9.8 – 0.49 = 9.31 N** N.B. up thrust increases as depth increases for fully submerged objects, the upthrust is constant Fupthrust = ρghA, where h = height of objectFor an object to float its upthrust must be equal to its weight.FupthrustFweightFLOATING & SINKINGi.e. Fupthrust = Fweight(so, Fresultant = 0 N)If the object gets heavier, it will sink deeper to increase its upthrust.If it becomes too heavy, Fupthrust < F weightand the object will sink. Question
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