Why is the centroid the balancing point of a triangle?

Answer 1

This is sometimes referred to as center of mass, as well. If you could take the vector sum of all the torques produced by all of the 'point-masses' to this particular point they will net to zero. For simplicity, consider a weightless see-saw.

On the right side of the see-saw is a person weighing 100 pounds, who is 6 feet away from the pivot point. This produces (100 pounds force) x (6 feet ) = 600 foot-pounds force of torque, in the clockwise direction. On the other side of the see saw is a 200 pound person at 3 feet away from the pivot. This will produce (200 pounds force) x (3 feet ) = 600 foot-pounds force of torque, in the counter-clockwise direction. So the see-saw is balanced.

Now for each 'point-mass' (this is an infintessimaly small area with an associated small mass), a certain distance away from the centroid, there would be an equal mass the same distance away on the other side, but a vertex is farther away than the opposite side, so there will be two points, each at an angle from the centroid to a point which are a shorter distance, but add to balance the farther points. This is kind-of hard to explain without pictures.