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Transcript
Archimede’s Principle • An object immersed in a fluid has an upward (buoyant) force equal to the weight of the fluid it displaces. FB = gV • FB = buoyant force • = mass density of the fluid • g = acc. due to gravity • V = volume of the fluid displaced Floating • Since apparent weight = 0, the weight of the object = weight of the fluid displaced (or buoyant force). Wapp = 0 so Wobj = FB = Wfd • Volume of the fluid displaced = volume of the submerged part of the object. Vfd = Vsubmerged • density of the object < density of the fluid Sinking • The object can’t displace enough fluid to equal its own weight. Wobj > FB • The volume of the fluid displaced = the volume of the object. Vfd = Vobj • Wapp = Wair - FB Wapp = apparent weight Wair = weight of object in air (= mg) FB = buoyant force (= Wfd = fVg) Pressure • Force per unit area • Units: Pa (N/m2) • P = pressure • F=force • A= area F P A Pascal’s Principle • Pressure applied to a fluid is transmitted throughout that fluid unchanged in all directions. • Pressure increases in a fluid with depth • P = g h, where = density of fluid, g= acc. due to gravity, and h = height of the fluid column • The shape of the container has no effect on pressure. Only Depth! The pressure at the bottom of the each is the same. Hydraulics • Machines using hydraulics use fluids to multiply forces. • These machines have a small piston and a large piston connected by a chamber filled with hydraulic fluid. • P1=P2 so… F1/A1 = F2/A2 Pressure is constant • MA = F2 / F1 = A2 / A1 Bernouilli’s Principle • As the velocity of a fluid increases, the pressure exerted by that fluid decreases. • (not valid for turbulent flow) Applications of Bernouilli’s Principle • Lift on an airplane wing - air has to travel farther over the top of the wing, so velocity is greater and pressure is less on top of the wing than underneath. • Spoilers on a race car - opposite of the airplane wing.