Equilibrium and Newton’s 1st Law

Dynamics deals with systems where one or more object is in motion. Newton’s Laws of motion are used to describe and predict the effect of forces that act on objects.

Objects that are stationary or moving with constant velocity are said to be in equilibrium. The acceleration of an object at equilibrium is zero.

A system at equilibrium can also be described in terms of the forces acting on that object. An object at equilibrium will have a net force of zero acting on it. Note that an object at equilibrium can still have forces acting on it – the sum of those forces will = 0.

Equilibrium and Newton’s Law

Newton’s first law of motion is based on the concept of equilibrium:

A body at rest, or moving with constant velocity, will remain at rest or moving with constant velocity unless an unbalanced force acts on it.

An unbalanced force will result in acceleration and this changes the state of motion of the object. The object will no longer be in equilibrium.

There are two types of equilibrium: Static and Dynamic.

Static equilibrium exists if all the forces acting on a body add to zero, and the body is at rest. ie a table or a phone sitting on it.

Dynamic equilibrium exists if all the forces acting on a body add to zero, and the body is moving at constant velocity. ie a bike travelling at a constant speed on a straight road.