Relative motion is the branch of physics in which we study the motion of a body with respect to another moving body. To understand relative motion, consider an example. Suppose you are riding a bicycle. You are standing on a street next to the railway track. A train passes in front of you with a speed of 60 km/h. Now you start moving in the opposite direction of train. Now the next train is coming towards you with the same speed as the last train passed you. You are moving with a speed of 10 km/h towards the train.

Now the speed of the train would appear to you as 70 km/h. Similarly if you are moving toward the direction same as the train with the speed of 10 km/h and the train is at a speed of 60 km/h, the speed of train appears to you as 50 km/h. This is the relative motion. Everything in this universe is moving with the relative motion. If the frame of reference is same then the actual speed would appear to you. Most commonly this effect is observed in the driving while overtaking the other cars. The consideration of frame of reference should be kept in mind while observing the relative motion

Now the speed of the train would appear to you as 70 km/h. Similarly if you are moving toward the direction same as the train with the speed of 10 km/h and the train is at a speed of 60 km/h, the speed of train appears to you as 50 km/h. This is the relative motion. Everything in this universe is moving with the relative motion. If the frame of reference is same then the actual speed would appear to you. Most commonly this effect is observed in the driving while overtaking the other cars. The consideration of frame of reference should be kept in mind while observing the relative motion