They kept the energy, together kinetic (related to they speed) and potential (related to their position). They actual speed/velocity has been changing all the time as the energy has been exchanged one for the other.

That is why I think FB and others might been quietly lobbying for this solution. This way they can stll be predatory, as long as the kids pretend to be adult. Or just abuse adult users. The alternative, of not being evil, is not compatible with their business model. But it is the business model that should be banned, not socializing online by teenagers.