Where Does Nuclear Energy Come From?

Physics students in their examination answers often write that "nuclear fission releases energy because mass is converted into energy" .  At a first glance this statement may seem plausible due to Einstein's well known equation. However, upon closer consideration, based on remembering that the protons and neutrons are rearranged into different combinations in the reaction and so their total number does not change, where does the mass that is converted into energy come from?

Some Mathematical Meandering I

It is often refreshing to spend time wandering through the fields of the world of mathematics, looking at the scenery and following the laneways to see how they link-up. Most students of mathematics know that the sine of an angle in a triangle is the ratio of the length of the side opposite to the angle to the length of the hypotenuse. This is written as sin(x), where x is the angle. In a number of applications of physics our calculations require us to to divide sin(x) by x. As this occurs frequently, we give this operation the name of sinc(x). However, at one point this function gets into trouble. When x = 0, sinc(0) is 0/0. Is this equal to 1?