Kennedy's theorem

Kennedy's theorem states that in a system where multiple forces or motions act together, the combined effect at a joint or point can be understood by “adding” their influences in a specific way. Specifically, if multiple links or components move or rotate, their instantaneous centers of rotation—points about which they are turning at that moment—are aligned along a straight line. This alignment helps engineers analyze complex motion systems by breaking down movements into simpler parts, making it easier to predict how the whole system will behave at any given instant.