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I know that the conversion formula between friction coefficient and surface roughness is directly proportional. I want to know that there is a conversion formula. I know the friction coefficient and want to know what the fine roughness is
There is no formula to calculate this
At present, it is not clear what causes the friction to reach
The friction coefficient has light with the contact surface and material. Therefore, the degree of roughness cannot be determined. The material should also be determined
It can only be empirical estimation
What are static friction coefficient and dynamic friction coefficient? What is their calculation formula?
I haven't heard of the static friction coefficient. It should be related to the maximum static friction
When the object is stationary, the friction force it receives can be any value from zero to the maximum static friction force, and can change with the change of external force
Dynamic friction is different. As long as it moves, the friction coefficient is a fixed value, the positive pressure on the contact surface remains unchanged, and the dynamic friction remains unchanged
How to check the modi friction coefficient diagram How to check the friction coefficient when the Reynolds number and relative roughness are certain?
Find a curve of the corresponding relative roughness from the coordinates on the right side of the modi friction coefficient diagram, or interpolate a curve, and then find the corresponding Reynolds number from the abscissa. Make a longitudinal straight line to intersect with this curve at a point, and make a straight line parallel to the abscissa to intersect with the ordinate on the left. The ordinate value of the intersection is the value of the friction coefficient "in"
As shown in the figure, a small ball with a mass of M is hung with a thin rope with a length of L and placed on a smooth spherical surface with a radius of R. the minimum distance from the suspension point to the spherical surface is D, then how much pressure does the small ball have on the spherical surface? What is the tension of the rope?
The stress analysis is shown in the figure:
It can be seen from the figure that the force triangle △ g'na ≓ △ toa
Mg
d+R=T
L
mg
d+R=N
R
N=mgR
d+R
T=mgL
d+R
Therefore, Newton's third law can obtain the pressure Mgr of the small ball on the spherical surface
d+R； The tension on the rope is MGL
d+R．
A: the pressure of the ball on the spherical surface is Mgr
D + R, the tension of the rope is MGL
d+R．
As shown in the figure, an object with a mass of M is pulled by a string through a smooth hole to make a uniform circular motion on a smooth horizontal plane. When the tension is a certain value f, the rotation radius is R. when the tension gradually decreases to f / 4, the object makes a uniform circular motion with a radius of 2R. What is the work done by the object to overcome the tension? Want process
According to the kinetic energy theorem
F=mvv/r,E=1/2mvv=1/2Fr
So we can express the kinetic energy before and after, and its change = work done. We can't use w = FS because they don't know
The answer is 1 / 2fr-1 / 4Fr = 1 / 4Fr. It's easy to convert it into kinetic energy change
As shown in the figure, there is a smooth small hole o on the smooth horizontal desktop, a light rope passes through the small hole, one end is connected with a small ball a with a mass of M = 1.0kg, and the other end is connected with a weight B with a mass of M = 4.0KG. Find: (1) When a ball moves in a uniform circular motion along a circle with radius r = 0.1M, = 10rad / s, what is the pressure of B on the ground? (2) What is the angular velocity of ball a when object B will begin to leave the ground? (G is 10m / S2)
Establishing and studying physical models of practical problems can not only describe physical laws more generally, more simply and generally, but also solve practical problems simply. In the application of the law of conservation of momentum, many topics are the deformation and comprehensive application of the "bullet hitting wood block" model. When analyzing and solving such problems, associative models, through analogy and equivalent methods, The model of "bullet hitting wood block" is generally divided into two categories, and the specific analysis is as follows:
I. category I: the bullet hits the wooden block but fails to penetrate
Model 1 as shown in Figure 1, the wood block with mass m is placed on a smooth horizontal plane, and the bullet with mass m shoots at the wood block horizontally at velocity V0 (assuming that the bullet is subject to constant resistance in the wood block), but does not penetrate the wood block. Calculate the maximum velocity of the wood block?
(1) How long does the object M2 leave the car?
(2) during the sliding of object M2 on the vehicle, what are the positive work of M2 on the friction of the trolley and the negative work of the friction of the trolley on M1? （g＝10m／s）
(1) after the object M2 slides onto the trolley, it starts to make a uniform deceleration movement to the right under the action of the trolley sliding friction to the left. At the same time, the trolley starts to make a uniform acceleration movement to the right with an initial speed of zero under the action of the trolley sliding friction to the right. When the object leaves the trolley, that is, the position displacement difference between the two is equal to the vehicle length L. let the accelerations of the object and the trolley be A2 and A1 respectively, From Newton's second law
a1＝（ μ m2g）／m1＝ μ g＝0.5m／s,
a2＝－（ μ m2g）／m2＝－ μ g＝－0.5m／s．
If the time t object is separated from the trolley, then
L＝s2－s1＝（v0t－（1／2）a2t2）－（1／2）a1t2,
Substituting the values of A1, A2, l and V0 into the above formula can be obtained
T1 = 1s, T2 = 4S (rounded off)
(2) from T1 = 1s, the displacement of the object is
s2＝v0t－（1／2）a2t2＝2．25m．
The position of trolley is S1 = (a1t2 / 2) = 0.25m
W1 = μ mgs1＝0．125J,
W2＝－ μ mgs2＝－1．125J．
It can also be solved by the kinetic energy theorem. When the object is separated from the trolley, the speed of the object is
v2＝v0－a2t＝2m／s,
The speed of the trolley is V1 = a1t = 0.5m/s,
For the kinetic energy theorem for trolley, W1 = (1 / 2) m1v12 = 0.125j
Using the kinetic energy theorem for objects, we get
W2＝（1／2）m2v22－（1／2）m2v02＝－1．125J．
The essence of the "bullet hitting wood block" model is that the object realizes the momentum change, kinetic energy change and energy change of the object in the system under the impulse of a pair of force and reaction force (internal force of the system). If the system is not subjected to external force in the horizontal direction (or vertical direction), or the external force is negligible compared with the internal force, the total momentum of the system remains unchanged The scientific thinking method of "model" is used to broaden the "bullet hitting wood block", so as to solve difficult problems quickly and accurately, train students to solve more problems, solve more problems, and understand them thoroughly, so as to achieve the effect of cultivating students' innovative ability
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