the equation of motion for the weight at the location x + h is obtained: ∂ ∂ 2 ∂ ∂ t 2 u ( x + h , t ) = k m [ u ( x + 2 h , t ) − − u ( x + h , t ) − − u ( x + h , t ) + u ( x , t ) ] . If the array of weights consists of N weights spaced evenly over the length L = Nh of total mass M = Nm, and the total spring constant of the array K = k / N, we can write the above equation as