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?
In: 0
Nah. You define speed by the distance it moves over time, there’s no way of having speed without distance.
But that’s not a problem. There’s a bunch of other measures that are ratios. Frequency is literally “oscillations per second”, Joules are kilogram meters^2 /seconds^2. There are some fundamental measures, like length, mass and time, like you said, but almost all of the actual measurements we make are combinations of those fundamental measures.
As for “size” causing issues, there is no reason you cannot use the center of mass of the object for the speed in most cases. If the center of mass for your big object has the same speed as the center of mass for a small object, they’ll move the same distance.
If you can’t do that, you can integrate the different speeds of all the different parts and end up with a net speed anyway, so there’s never broken math.
Latest Answers