State law of conservation of momentum . A bullet of mass 10g is fired from a gun of mass 6kg with a velocity of 300 meter per second . Calculate the recoil velocity

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 : )

3. dark matter

empty space could also be a simple vacuum