Relative Motion

The laws of physics which apply when you are at rest on the earth also apply when you are in any reference frame which is moving at a constant velocity with respect to the earth. For example, you can toss and catch a ball in a moving bus if the motion is in a straight line at constant speed.

The motion may have a different appearance as viewed from a different reference frame, but this can be explained by including the relative velocity of the reference frame in the description of the motion.

Reference: http://hyperphysics.phy-astr.gsu.edu/hbase/relmot.html

If you are on a subway train in a subway station, you can see people standing or sometimes walking in the aisles of another train; your train or the other train might be moving in either direction. Sometimes it is hard to say what is moving! This means that the motion of a body always depends on a particular frame of reference. Galileo was the first person to formalize this concept, which is known as relative motion.

Click on website to see reletive motion in subway station demonstrations.

Refence: http://demonstrations.wolfram.com/RelativeMotionInASubwayStation/

(Galileo Galilei; 15 February 1564 – 8 January 1642) was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. )

(http://en.wikipedia.org/wiki/Galileo_galilei)