how come if you jump in a train you will land in the same spot but if you jump on top of the train you won't? i tried to make it make sense.

Well, it has to do something with the force of the train. It's pulling you, a force of gravity

However jumping off results in a different sort of energy, the train know is moving farther away as you jump down. So you end up in a different place

Explanation:

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.