We live in the bottom of deep sea of air called atmosphere. Air has mass so that it has some weight. The weight is a force thus it exerts force per unit area on us known as atmospheric pressure.
The pressure exerted by the atmosphere is called atmospheric pressure.
1 atmosphere = 1.01 * 10 5 N/m2
According to Archimedes principle:
“When a body is immersed in a liquid, it losses its weight or an upward thrust acts upon it which is equal to the weight of an equal volume of the liquid displaced.”
Proof of Archimedes Principle:
Consider a cylinder of length ‘L’ & area of cross-section ‘A’ immersed in a liquid of density
The depth at point ‘a’ = h1
The depth at point ‘b’ = h2
Pressure at point ‘a’ and ‘b’ is
Pa = pgh1
Pb = pgh
We know that
Thrust = PA
Thrust at point ‘a’ = pgh1A
Thrust at point ‘b’ = pgh2A
Net thrust = W [W=mg]
Net thrust = weight of liquid
This shows that upward thrust or the cylinder is equal to the weight of liquid displaced.
Apparent weight = actual weight – weight of the liquid displaced by
Results of Archimedes Principle:
(1) A body will float over a liquid if displaes liquid whose weight is greater than the weight of the body.
(2) A body will sink in a liquid if it displaces liquid whose weight is less than the weight of the body.