Suppose a piece of wood is floating inside a closed waterbottle and through a pump, air is pumped into the bottle. Will the wood float or sink?

remain floating as same as it is initially floating.

Suppose a piece of wood is floating inside a closed waterbottle and through a pump, air is pumped into the bottle. Will the wood float or sink?

 

Explanation) When air is pumped into the bottle, the air column just above the surface of water exerts more and more pressure on the surface of bottle as well as water. Hence the exerted pressure tries to compress the water by exerting force =( Pressure x area) in the downward direction, but since the water is incompressible and the force that is also acting on the wooden piece will increase the effective weight of the wooden piece consequently more buoyant force is required to balance the weight of floating piece. This implies that wooden piece starts to submerge more and more inside the water depending upon the force due to air column.

Let me explain you the laws of floatation

 

 

(i) The wt. of a body acts vertically downwards through centre of gravity of the body

 

(ii) The resultant upward thrust exerted on the body by the liquid i.e. force of buoyancy acts vertically upward through the centre of gravity of displaced liquid i.e. centre of buoyancy

 

 

(i) The wt of the body is equal to the wt. of the displaced liquid

 

(ii) The centre of gravity of the body and centre of gravity of the displaced liquid are in the same vertical line

 

The only essential condition for a body to float in a liquid is that the weight of the liquid displaced by the body should be equal to the weight of the body itself

 

Since air is pumped in side the water bottle, hence body will float until the wt. of the liquid displaced by the body is equal to the wt. of the body itself otherwise it will start submerge.