the law given in this chapter that describes the production of an emf by a changing magnetic flux is named after

i guess that visual aids present persuasive examples to what you are presenting, some factors would be theme (does it fit with the color, information, what you are presenting), size (can you see it, is it a big enough span of data/information), and overall look of the visual aid.

hope this : )

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement

a skateboard rolling across the street - apex