# Ball dropped from a moving train

Can anybody please explain why the ball dropped from a moving train appears to take a parabolic path w.r.t the frame of reference of a person standing at the platform?

Thanks

Nabeshin
Can anybody please explain why the ball dropped from a moving train appears to take a parabolic path w.r.t the frame of reference of a person standing at the platform?

Thanks

In the reference frame of the platform the ball has initial horizontal velocity equal to the velocity of the train. The vertical direction is the same observed on the train because both observers agree that gravity is acting on the ball causing an acceleration -g. But, in the platform's reference frame it already had x-velocity, and the resultant path is a parabola.

I am currently reading about this in Einstein's writings. When the person on the train drops the ball and looks down he just sees it fall straight down because it is moving at the same velocity he is.

However, a person standing on a platform (not in motion) sees the ball fall down and perpendicular to his view. (In two dimensional motion)
It is all about the reference point. Relativity is a very cool and interesting topic!

In the reference frame of the platform the ball has initial horizontal velocity equal to the velocity of the train. The vertical direction is the same observed on the train because both observers agree that gravity is acting on the ball causing an acceleration -g. But, in the platform's reference frame it already had x-velocity, and the resultant path is a parabola.

Thanks Nabeshin, your explanation makes sense.

Vijay

gmax137