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Suppose that you have a large number of knitting needles and thousands of beads which can slide along needles without friction. All beads are released from rest at the same time from a point A to slide down the needles.
Extension: In a real situation there will a friction force. The coefficient of friction is $\mu$. Suppose it is not dependent on the speed of a bead. Find the shape of beads after time $t$ and describe how it is changing.