This question stemmed from a conversation about measuring the speed of two very different objects. I realized that, unlike other measures that have their own units (length, mass, etc.), speed is measured using a ratio of distance and time. So I was wondering, does the size of the objects get factored into the measurement somehow? If speed is only ever measured using this distance/time approach (mph, for example), then wouldn’t the measure of speed become problematic since a large object is able to cover more distance than a small object?
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For rotational motion, there’s angular velocity, which is sometimes used. For instance RPM (revolutions per minute) in a car engine is independent of the size of the engine, piston size etc. just depends on how many times the crankshaft turns per minute.
Additionally you could say a second hand rotates at 1 RPM, a minute hand 1/60th of an RPM etc. regardless of the length of that second hand, it’s the same for a wristwatch as for Big Ben.
While this is excellent for rotating objects, this isn’t a good way of measuring velocity when you’re wanting to actually know linear velocity.
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