When the net forces acting on a particle is zero, that particle is said to be in equilibrium. If small displacements from equilibrium results in the particle staying close to the equilibrium point, the equilibrium is said to be stable, otherwise it is said to be unstable. When the ball is placed at the bottom of the bowl it is at equilibrium. When the ball is moved a small distance from the bottom, the ball stays in the vicinity, demonstrating the stability of the equilibrium. When the ball is placed on top of the bowl, it is also stable, but moving the ball slightly from this position results in a large final displacement, so the equilibrium is said to be unstable.

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