(a) What are fluids ? Name two common fluids.
(b) State Archimedes’ principle.
(c) When does an object float or sink when placed on the surface of a liquid ?

(a). All the substances which can flow easily are known as fluids. All the liquid and gases are known as fluids e.g. water, air, etc.

When an object is wholly (or partially) immersed in a liquid, a buoyant force (or upthrust) is experienced by the object which is equal to the weight of the liquid displaced by the object.

It can be said that:

The buoyant force on an object = weight of the liquid displaced by that object

(c). If the buoyant force exerted by the liquid is less than the weight of the object, the object will sink in the liquid. If the buoyant force exerted by the liquid is equal to or greater than the weight of the object, the object will float in the liquid.