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It is quite common that a physicist will make up terms and mathematics in order to explain certain complex physical situations more simply. One important example of this is a rotating system. If we watch two people playing catch on a merry-go-round (or the Earth), it is more convenient to calculate the forces, positions, etc. from a reference frame (point of view or coordinate system) that rotates along with the people. From this point of view, the two people are not spinning but we pretend they are stationary. What is the tradeoff? It turns out we introduce "fictitious forces". For instance, if you are in a car that turns sharply, it feels like you have a sideways force. Really, you are trying to move in a straight line, but the door of the car is accelerating you around the bend.