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Fluid Mechanics. Chapter 8. Mass Density. The concentration of matter of an object, measured as the mass per unit volume of a substance. Represented by the Greek letter ρ (rho) mass density ( ρ ) = mass/volume Units kg/m 3. Buoyant Force.
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Fluid Mechanics • Chapter 8
Mass Density • The concentration of matter of an object, measured as the mass per unit volume of a substance. • Represented by the Greek letter ρ (rho) • mass density ( ρ ) = mass/volume • Units kg/m3
Buoyant Force • Upward force exerted by a liquid on an object immersed in or floating on the liquid. • Because the buoyant force acts in an opposite direction as the force of gravity, the net force acting on an object submerged in a fluid, is smaller than the object’s weight. • Objects appear to weigh less in water than they do in air so the weight of an object in a fluid is the object’s apparent weight.
Your Turn! • Why does an air mattress float and a brick sink? Think of an answer and make sure you put it in terms of forces.
Eureka!!! • Archimedes’ Principle- Any object completely or partially submerged in a fluid experiences an upward buoyant force equal in magnitude to the weight of the fluid displaced by the object. • Does this mean that the buoyant force is just like weight (mg)?
Buoyant Force • FB=Fg(displaced fluid) • FB=mfg • In other words • The magnitude of the buoyant force equals the weight of fluid displaced • What does Fg equal? • Based on Archimedes’ Principle, what would be a good equation for FB?
Fg -FB =apparent weight • Fg-apparent weight= FB • Fg=mg • FB= ρ V g • Where did ρ V come from? • What is V?
Sink or float? Buoyancy Largest = Ascend Forces Balanced = Hover Weight Largest = Sink