Fizzics Fizzle: Beginner: Equilibrium

Equilibrium is also a very simple idea. Equilibrium occurs when all forces acting on an object cancels out (the net force is 0).

For example, an object at rest is at equilibrium. For a ball sitting on a table, gravity (which acts down), and the force that the table exerts to hold the ball up (called the normal force), cancel each other out.

However, if an object is moving at constant velocity (its speed and direction is not changing), is it in equilibrium? Since it is at constant velocity, that means it must not be accelerating. And since it is not accelerating, that means the net force must be zero. Therefore, it is in equilibrium. Once you think about it, it makes sense. For example, a car moving at a constant velocity has the force of friction (to slow it down), the force of the engine (to speed it up), the force of gravity (which makes it fall), and the normal force of the road (which holds it up). All these forces cancel each other, and the car is in equilibrium.

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Clyde Law, Chetan Taralekar, Jim Wang

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