If you jump whilst in a train why dosen't it move under you?

Im not sure as i am not that good at physic but ill tell you what i think the correct answer is.when you are in a train you are moving in the same direction as the train and at the same speed.i think when you jump up you carry on moving in the same direction though you would be slowing down however not fast enough to be noticable in the short time amount of time you are in the air.if gravity wasnt as strong and you could stay airbourne for longer you may land in a different part of the train.

When you jump vertically upward, you must fall to the same position where you have jumped from provided the train moves with uniform speed. This happens because of inertia of motion. How? Fine! The speed of train gets transferred to you when you are in contact with the floor. So you also move forward along with the train with same speed when on the fly. However, if the train accelerates when you are on the fly, the train must move under you.