"relative to the environment it's in" has no meaning! Any object moves relative to a myriad of possible refence frames which are also moving; there is no unique stationary refence frame; i.e. environment (Einstein's theory of relativity). The trajectory and speed one observes for a moving object depends on which refence frame one chooses. So you cannot define a fastest movement, only movement relative to the refence frame you have chosen; most probablynthe one within which you think that you are stationary. Even kinetic energy is not an absolute quantity but depends on the reference frame it is measured relative to.

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