Aviscous liquid is sheared between two parallel disks of radius �, one of which rotates with angular speed ω, while the other is fixed. the velocity field is purely tangential, and the velocity varies linearly with z from: �; = 0 at � = 0 (the fixed disk) to the velocity of the rotating disk at its surface (� = ℎ). derive an expression for the velocity field between the disks.

Upper disk rotates at a constant angular velocity. The velocity at any height from stationery disk, say at x metres

where v is tangential velocity at radius r from the centre of disk

The radial component of velocity is given as

The z component of velocity is also given as  

W=0

Total velocity,

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.