In everyday life we do not suspecting, often use the benefit, which tells us the formula of Euler. What is the site, not as a string wound upon the roller, the role of which in this case plays the other part of the same string? Fortress all kinds of sites - ordinary, "bowline", "sea", ties, bows, etc. depends entirely on friction, which here many times increases due to the fact that the cord wraps itself around him, as the rope around the tables. This is easily seen by tracing the curves of lace in the node. The more curves, the more times the string wraps itself around him - the more the angle navipane" and, therefore, the stronger the node.
Unconsciously uses the same circumstance and tailor, sewing a button. He often winds the thread around the captured stitch plot of matter and then cuts off her; if only the thread is strong, the button will not otpiratsya. It uses a familiar rule: with the increasing number of turns of the thread in arithmetic progression fortress sewing increases in geometric progression.
If there were no friction, we would not be able to use the buttons: yarn was unwound, would be under their weight and the buttons fell off.