Two massive objects move towards each other because of gravitational attraction. If the gravitational force between the spheres is 100N, what is the force between them when the
distance is halved?

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 : )