V-belt transmission power is commonly used in factories，And rarely use flat belts，This is because the triangular belt can generate significant static friction without slipping。You only need two books on hand to compare the friction force of a triangular belt with a flat belt through experiments。

  *Choose a book with a hard cover，For example, a small dictionary，A slightly larger hardcover book。Wrap the written pages of these two books in the same paper as the inside pages，Make Highlight 。

  (1)Imitate the situation of a flat belt：Lay the small dictionary flat on a large book，Gradually lift one end of the large book，Until the dictionary just started to slip，Record the inclination angle of the inclined plane at this timeθ1。Set the quality of the dictionary tom，Between the dictionary and the book cover *Large static friction forcefmax=mgsinθ1。

  (2)Following the situation of the triangular belt：Image1.7-2Shown，Spread the small dictionary across the large book，Raise one end of the large book as well，To the small dictionary, just about to slide and stop，Set the angle between the spine of the book and the horizontal plane asθ2，be *Large static friction forcef′max=mgsinθ2。Here, the small dictionary is compared to a triangular groove，Big books are compared to triangular belts，this *Large static friction forceIt is also equivalent to the triangular groove and triangular belt *Large static friction force。

  In the experiment，You can see thatθ2thanθ1Much larger。This indicates that the triangular belt can generate much greater friction force。

  Why can the triangular belt break outthanThe flat belt has much greater static friction force?Can contact the diagram1.7-3Let's make a concise analysis。Gravity on dictionaryGAnd elasticityN1，N2phase equilibrium，NamelyN1、N2The resultant force andGEqual in size、Opposite direction。Due toN1、N2The angle between them is very large，therefore，N1、N2thanIts combined forceMuch larger，thereforeN1、N2greater thanG(In a flat beltN=G)。From this, it can be seen that，The static friction force between them *Big value alsoMuch larger。