Thursday, October 4, 2018

pressure - Buoyant force in an elevator


I can't understand why buoyant force exerted by the liquid on a ball attached to a rope in a box having liquid of density $p$ moving in an elevator moving with acceleration $a$ has buoyant force as,



$B= Vp(g+a)$ (V is the volume immersed ,i.e. the volume of ball itself)


Why its not $B=Vpg$ ? Please try explaining mathematically/by using equations please.


enter image description here



Answer



This becomes clearer if you think about the liquid, not the ball.


The buoyant force is caused by the pressure of the liquid. The pressure is caused by the weight of the liquid. The weight is cause by gravity.


When an elevator accelerates downward, it is just as if gravity had become weaker. The weight of the fluid decreases. The pressure decreases. The buoyant force decreases.


This question may also help. How does buoyancy work?


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