Define pressure. Give its SI unit.
The total force applied per unit area is called pressure.
Mathematically,
Pressure (P) = Force (F) / Area (A)
Its SI unit is pascal (Pa).
Prove that upthrust (U) = (h2 - h1)Adg = Vdg, where the symbols having their usual meanings.
Let us consider a cylinder of height 'h' and uniform CSA 'A' is immersed in a liquid of density 'd'. If h1 and h2 are the depths of the upper and lower surface of the immersed cylinder then,
Force on the upper surface, F1 = P1 . A = h1dgA
Force on the lower surface, F2 = P2 . A = h2dgA
Here, g is the acceleration due to gravity.
Now, upthrust (U) = F2 - F1
= h2dgA - h1dgA
= (h2 - h1)dgA
= hdgA Since h2 - h1 = h
= Vdg Since Ah = V
= mg Since Vd = m