It’s difficult to split BECAUSE it’s really small – and because lots of energy is holding it together! In our big world, things stick together because of gravity, because of magnets, or because they’re charged, or because they’re glued. In the small world of the nucleus, there is an extra binding force called the nuclear force, which is very strong, but only for things that are one 1000000000000000th of a metre apart! if it’s three times that tiny distance it already stops working!
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