Central bank digital currency reference
Huang Zhen, director of the Institute of financial law of Central University of Finance and economics, said that digital currency mainly refers to the form of currency and will not cause currency shrinkage. The issuing scale of money is still controlled by the central bank, while the issue of paper money or digital money is just a change of form< In addition, Huang Zhen mentioned that the issue of digital currency is still in the stage of discussion, which is an innovative mechanism of currency value symbol, and many problems are still under study. However, in practice, people are more and more inclined to use e-banking and e-payment rather than carrying notes. Under this trend, the number of banknotes in circulation in the future may decrease
the central bank's issuing of digital currency is still inspired by encrypted digital currencies such as bitcoin and lettercoin, and so is the token of European crowdfunding platform. The digital currency issued by the central bank has monetary attributes, while the token of European crowdfunding platform can only be a kind of asset certificate, a niche proct.
2019 August 21st, the official account of WeChat central bank released two articles on digital currency.
f=N μ N is the positive pressure, that is, the pressure acting on the contact surface, μ It is the dynamic friction coefficient, which refers to the influence factors of the roughness of the contact surface on the friction. Or use the balance f = f; It's only used when it's stationary or moving in a straight line at a constant speed, but it's the most used in junior high school
the so-called friction is the force that hinders the relative motion of the object, and the direction of friction is opposite to the motion direction or relative motion direction of the object. The conditions of friction are as follows:
(1) two objects must contact each other
(2) there was extrusion between two objects(3) there is a tendency of motion or relative motion between two objects
If an object is stationary on a horizontal plane, it will not be affected by friction if it is not pushed or pulled. If thrust or pull is received, it belongs to the category of static friction. The size of friction is equal to that of pull or thrust, and has nothing to do with the gravity or pressure of the object. Only the maximum static friction is related to the pressure or gravity on the object
if the object is not pushed by 10N force, the object will be subjected to static friction, which is equal to the thrust. Just push with 15N force, and the friction force on the object is the maximum static friction force. If the thrust force is increased later, the friction force will not change. Theoretically, the sliding friction of objects is less than the maximum static friction, but it is generally considered that they are equal
The friction force is f = 15-10 = 5N 
extended data:
methods to increase beneficial friction
(1) increase the roughness of contact surface
(2) increase the pressure (3) change rolling friction into sliding friction (1) replace sliding friction with rolling friction(2) make the contact surface separate [form a layer of air cushion or magnetic suspension on the contact surface of the object]
(3) decrease the pressure (4) rece the roughness of the contact surface In engineering technology, people often rece friction by applying lubricating oil. The science of this problem is called tribology, which is a branch of mechanical manufacturingIf two objects, which are in contact with each other and squeeze each other, but relatively still, only have a relative sliding trend under the action of external force, but do not have relative sliding, then the force between their contact surfaces hindering relative sliding is called "static friction". When the static friction increases to the maximum, the object will move
size: the static friction varies according to the external force, but there is a maximum value, which is called the maximum static friction. The maximum static friction is slightly greater than the sliding friction
direction: tangent to the contact surface, opposite to the direction of relative motion trend
On the basis of a large number of experiments, G. amunton and C. - A. de Coulomb proposed the following law of friction in 1699 and 1781:① the friction between two objects in contact does not exceed a certain maximum value, which has nothing to do with the size of the contact area
(2) the maximum value of friction is proportional to the normal pressure n between two objects (3) the direction of friction is opposite to the sliding direction of the object, and its magnitude is directly proportional to the normal pressure n between the two objectsthe above conclusion is only a rough empirical rule, but because it was found in the early days of mechanical science, it was called the law of friction, also known as Coulomb's law