The equation of motion for a particle undergoing SHM is F=-kx, where F is the resultant force on the particle and x is the displacement of the particle. k is a scalar, known as the spring constant. F is proportional to x and the direction of vector F is opposite to that of vector x. A solution of the equation of motion is x=Asin(wt+phi). A is the amplitude or maximum displacement of the particle from the equilibrium position.
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