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The Weighty Problem of Defining Mass
Why Defining Mass Is Hard
In a previous article, I elaborated on how it might be possible to reduce the definition of the study of Physics in high school to the study of the interactions between mass and energy. But that left me with a bit of a problem, as one of my more perspicacious students asked me a question: what is “mass” made of? So here I try to elaborate on that question.
Think you know what mass is? Try explaining it without using the word “weight.” It’s trickier than it sounds. Imagine you’re playing dodgeball with friends, but you only have two balls: a ping-pong ball and a bowling ball. Both are hurled at you at the same speed. Which one would you rather be hit by? The sensible answer is the ping-pong ball: the bowling ball would hurt a lot more. Why? Because of mass. We all intuitively get that a bowling ball has more “mass” than a tiny ping-pong ball, so it packs a bigger punch. But ask a physicist what mass actually is, and you might get an awkward pause or a very long answer. It turns out “mass” is a simple idea that becomes a massive headache when you try to define it precisely. Is it the amount of matter in an object? The displacement you observe on a scale? The resistance you feel when pushing something heavy? Or some mysterious energy congealed into physical form? The answer is all of the above — and then some…
