Frustum
Introduction
In our day to day life we see objects like bucket,basket,glass,dustbin etc . They are of frustum shape.
If a right circular cone is cut off by a plane parallel to its base, then the portion of the cone between the cutting plane and the base of the cone is called a frustum of the cone.
To see how a frustum is created right click on the image and then select play option
Height The height or thickness of a frustum is the perpendicular distance between its two circular bases.
Slant Height The slant height of a frustum of a right circular cone is the length of the line segment joining the extremities of two parallel radii, drawn in same direction,of the two circular bases.
If h is the height, l the slant height and r1 and r2 be the radii of circular bases of a frustum of a cone , then
Volume of the frustum = 
h ( r12 + r1r2 + r22 )/ 3
or h/3(A1 + A2 + √A1A2) where A1 and A2 denote the areas of circular bases
Lateral surface area = l ( r1+ r2 )
Total surface area = ( r12 + r22 ) + l ( r1+ r2 )
Slant height of the frustum = √(h2 + (r1 - r2)2 )
Height of the cone of which the frustum is a part = h r1/ (r1 - r2)
Slant height of the cone of which the frustum is a part = lr1 /(r1 - r2)