Question

What does relative motion mean?

Answer 1

When we talk about the motion of something, we first determine a reference frame and then according to this reference frame we analyze the motion of the object. For example, suppose you are in a bus moving with the velocity of 50 m/s to the east and a truck passes you with a velocity of 60 m/s to the east. When the truck is next to the bus you feel that you are moving backward (to the west). Similarly, if the truck has the same velocity of 50 m/s to the east as the car, the truck appears to be stationary. All these are examples of relative motion. The velocity of the moving objects with respect to other moving or stationary object is called “relative velocity” and this motion is called “relative motion”. Reference frame is quite important in physics. We do all calculations according to the reference frame. For instance, if you observe a plane flying in the air, the velocity of that plane with respect to you is the sum of the velocity of the plane with respect to wind and that of the wind.