User:Zachem/Sandbox

FRICTION BETWEEN SHEETS

Ever tried – and duly failed – to pull apart two interleaved phone books? The difficulty in separating them is caused by the friction between the sheets, which is amplified by the huge number of pages in a directory. However, friction only occurs when two surfaces are pushed together and researchers were not sure how exactly this happens. Gravity was one explanation, but this can be refuted by holding the directories vertically. They also found that a relatively small increase in the number of pages has a dramatic effect on the pulling force necessary to separate them, so that a 10-fold increase in pages creates a four orders of magnitude increase in the force.