Another way that does not require any changes is if the arrow is made of multiple particles (which they are). Then some portion of the particles may move from s

Another way that does not require any changes is if the arrow is made of multiple particles (which they are). Then some portion of the particles may move from step to step. These particles then interact with others which are stationary, passing their motion to them for the next step. Thus the total speed of any composite object would be the ratio of how many of the particles are "moving", to how many are "stationary" at that step.