The First Law is concerned with changes in velocity caused by non-zero net forces.
In
the animation above we see an object (blue box) that is already moving
along when we encounter it. As long as we do not push or pull it, as
long as it does not run into something else or rub against something
else, it will continue to move in a straight line at constant speed. It
will continue to do this on its own without the need for any influence
from other agents.