Question

a) Explain clearly why an object need not "be rotating" in order to have a moment of inertia, and give an example. (Hint: Can you calculate the moment of inertia, whether or not the object is rotating?)

b) Explain clearly why an object need not "be rotating" in order to have a nonzero angular momentum, and give an example. (Hint: use L = r x p.)

Answer 1

a) the moment of inertia is not a property due to motion instead it is a property that decides the effect of mass and dimensions on motion, its the same as mass, an object need not be accelerated in order to have mass but mass plays a role in acceleration , a=F/m.. likewise moment of inertia depends only on mass, and the location of axis of rotation, and both of these have nothing to do with a body at rest or rotating.

b)   again angular momentum is not confined to rotating bodies, any body that can describe an angle with the line joining a point (about which angular momentum is to be found) , so a body moving in a straight line can also describe an angle and thus have angular momentum.. and moreover the value Mvr does not involve angular velocity..    while moving from A to B in a straight line an angle can still be described about point P. thus have angular momentum