One atom of uranium has 92 protons and about 145 neutrons in its nucleus. So make 92 small balls of paper… no, that would be too hard. Make a bunch of small balls, the size of the tip of your finger, by crumpling up scraps of paper. You should make about half of them one color (protons) and the other half another color (neutrons). Make at least fifty balls, even if you don’t have enough energy to make 237. You might want to work in groups.
Try to fasten all of these little balls together using plenty of rubberbands into one big ball: the nucleus of the atom. The rubberbands represent the strong nuclear force. It’s pretty hard, right? Real uranium atoms find it pretty hard too. Use plenty of rubberbands. (TIP: if you can’t get them all to stay together, try making littler groups of 3-5 balls and then fastening the groups together.)
Now imagine that you’ve set off a nuclear bomb and split this atom into smaller atoms. Divide your atom into little groups of three or four paper balls and wrap each group with a rubberband to keep it together. It should be easier to keep the littler groups together. So you’ll end up with some leftover rubberbands. Those leftover rubberbands represent the energy that makes the fire and heat of a nuclear explosion.