what makes a boat float ?what males an ice sink on a beer??

An archimedes principle : When an object is immersed in a liquid is buoyed up by a force equal to the weight of the fluid displaced by an object . fluid displaced has a weight W= mg ;mass can be provided by density and its volume .W=PVg

the buoyant force does not depend on the weight or shape of the submerged object, only on the weight of the displaced fluid.


If the density of the object is greater than that of the fluid, the object will sink. If the density of the object is equal to that of the fluid, the object will neither sink or float. If the density of the object is less than that of the fluid, the object will float.


Despite the enormous size of some ships, they are basically metal shells filled with air, and are less dense and lighter than the water they push aside, which allows the boats to float.


Density of the ice is much greater than the water i.e it sinks 

How an aeroplane fly?

how wings generate lift ?

 

A cross section an airplane wing will show the top surface to be more curved than the bottom surface. This shaped profile is called an 'airfoil'. During flight air naturally flows over and beneath the wing .

the air moving over the top of the wing has more distance to cover (because of the curvature it is forced to follow)  in the same amount of time as the air passing below the wing, it has to move faster.

Faster moving air is less dense than slower moving air, so this speed difference results in a lower air pressure on top of the wing, and a higher air pressure below the wing (so the pressure is force per unit area so upper wing has more surface area so the pressure would be less than the lower wing) The result of this pressure gradient is that the wing, and hence the plane, is pushed upwards by the higher pressure.