Expert: Sue Kayton - 1/15/2009

Question
what does a reference point have to do with the motion of an object?

Answer
Imagine you are riding in a train.  The train is sitting still in the station.  You dribble a basketball up and down.  The ball moves up and down, but has no sideways motion.

Now the train starts moving.  To an observer sitting inside the train with you, the basketball continues to just move up and down.  But someone standing outside the train, looking in through the windows, will see the basketball move forwards in addition to its up-and-down motion.

So your perceived motion is relative to the reference point of the observer.