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HIGHER PHYSICS

HIGHER PHYSICS. Upthrust, Floating & 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 & p = ρ gh So, F upthrust = ρ ghA. Resultant force on object,

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HIGHER PHYSICS

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  1. HIGHER PHYSICS Upthrust, Floating & Sinking

  2. Any object placed in a fluid receives an upward force, due to the pressure at that depth. Fupthrust h Fweight surface area, A liquid density, ρ UPTHRUST i.e. F = pA & p = ρgh So, Fupthrust = ρghA Resultant force on object, Fresultant = Fweight - Fupthrust

  3. Example – 1kg iron mass (see Virtual ‘H’ Physics) mass, m = 1 kg, Fweight = mg = 1 x 9.8 = 9.8 N area of base, A = 0.0025 m2, depth, h = 2 cm = 0.02 m Fupthrust = ρghA = 1000 x 9.8 x 0.02 x 0.0025 = 0.49 N Fresultant = 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 object

  4. For an object to float its upthrust must be equal to its weight. Fupthrust Fweight FLOATING & SINKING i.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 weight and the object will sink.

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