Phylum porifera

PORIFERA

• 1, Water canal system_
  
  body wall encloses a cavity (spongocoel).water enters through pores (ostia) and goes out through an osculam , by the action of flagellated cells             (collar cells / choanocytes)

Why Bf3 's dipolemoment is zero?

         The dipolemoment of
         Bf3 become zero . why?

Because B-f bonds are oriented at an angle of 120° to each_other  , the three moment gives a net sum of zero . As a resultant of any two is equal and opposite to the third 

Theorem of parallel axis

Parallel_axis theorem 

The theorem states that,
            the moment of inertia of a body about any axis is equal to the sum of moment of inertia
   of a body about parallel axis ,passing through centre of mass. 
               And product of mass of the body and the square of the distance between the two axis

in this figure ,

According to parallelaxis theorem

Moment of inertia about 

AB= MI of CD + Ma*2

ie,       I= Icm + Ma*2