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Wrap a rope once around a rough tree branch or post. Attach a heavy bucket to one end and try to hold it by the other (Fig. 6.43). Add one more turn and repeat. Each extra turn increases the grip, increasing friction and reducing the force needed. The reduction is much larger than expected, showing friction does not increase in a simple linear way — small changes in contact lead to large changes in force. This is also how a rope and post hold large ships at a pier.
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With one turn it is hard to hold the bucket; with each extra turn it becomes dramatically easier, even though you only added one loop. This shows friction from a wrapped rope grows very rapidly (not linearly) with the number of turns. The same effect lets a few turns of rope around a bollard hold a massive ship at a pier with little human effort.
