#### werehk

PHF Hall of Fame
When an object is not homogeneous, on a smooth level plane, the centre of gravity may not lie on the same line as the normal reaction, why?

so how can I determine where does the normal reaction acts on the body?

For the chapter on moment, when a ladder is leaning against frictionless wall,why is there a force (F2)at the bottom of ladder with is not perpendicular to the smooth road surface but inclined at a certain angle? Is it the normal reacation force?

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#### topsquark

Forum Staff
When an object is not homogeneous, on a smooth level plane, the centre of gravity may not lie on the same line as the normal reaction, why?

so how can I determine where does the normal reaction acts on the body?

For the chapter on moment, when a ladder is leaning against frictionless wall,why is there a force (F2)at the bottom of ladder with is not perpendicular to the smooth road surface but inclined at a certain angle? Is it the normal reacation force?

The normal reaction force is defined to be perpendicular to the surfaces in question. (The word "normal" is a five dollar term for "perpendicular.") So F2 can't be the normal reaction force.

I strongly suspect that F2 is the combined reaction force of the normal and the static friction forces on the ladder at that point. At least, F2 points in the direction you would expect that combined force to be in.

-Dan

werehk

PHF Hall of Fame