[DrStalker]

They could do a little comparison of existing technologies:

Chemical rockets - put fuel and oxidizer together, burn them, resulting gas is shoved out the back and pushes the rocket forward.

NERVA - reaction mass is heated by a nuclear heat source, resulting gas is shoved out the back and pushes the rocket forward.

Ion thruster: reaction mass (such as xenon) is charged electrically using a grid and the resulting ions are shoved out the back and pushes the rocket forward.

CAT: reaction mass (such as water) is charged electrically using a glass bottle thingy and the resulting plasma is shoved out the back and pushes the rocket forward.

Shove that in an infographic and you can get the basic concept across to someone who knows high-school physics and sound convincing to people that don't even have that level of background knowledge.

http://en.wikipedia.org/wiki/NERVA http://en.wikipedia.org/wiki/Ion_thruster