Sometimes objects move within a reference frame that is moving itself. Picture an airplane flying on a windy day. Visit the physics classroom to see an example.

Watch the following video showing a plane flying at almost the same speed as the wind.

If the plane is flying with airspeed of 120 m/s in the same direction as a 30 m/s wind, it will in fact be moving at 150 m/s relative to the ground. Similarly, if it flies against the wind, it will only be moving at 90 m/s relative to the ground.

Another example of this type of relative motion would be a boat moving with or against a current on a river.