Toppling giving example of a block on horizontal surface?

[Shahid0072]

Please explain me the toppling giving example of a block on horizontal surface? Is friction necessary? What's its deal with center of gravity?

 

[torquil]

I'm not completely sure I understood the question completely, but here goes:

If the centre of mass of the block is not above the contact area between the block and the table, it will start to move (fall over completely if there is nothing else that stops it). This happens whether there is friction or not.

Torquil

 

[Shahid0072]

But how can center of mass ever be below contact point..I mean contact point is at lowest point on the surface..When does a block topple?

 

[torquil]

Ah, I meant that either the centre of gravity is "above the contact area", or to the side of it. Not under it :-) If it is to the side of the area of contact, then you can prove that it starts to rotate to the side by considering the torque of gravity upon the object, with respect to some appropriately chosen axis.

TOrquil