How to calculate sliding friction
Publish: 2021-05-07 19:13:46
1. You can't withdraw money, can you? help
2. The formula of sliding friction f = UN
where n is the pressure, and N = mg
u is the sliding friction coefficient on the horizontal ground, which is related to the material.
friction
1, friction
(1) definition: when two objects in contact with each other are about to move or have moved relative to each other, they will proce a force on the contact surface to hinder the relative movement, This kind of force is called friction.
(2) the friction between objects must have the following three conditions:
first, the objects contact and squeeze each other
Second, the contact surface is not smooth
Third, there is a relative movement trend or relative movement between objects.
2 Sliding friction force
(1) definition: the friction force generated when an object slides on the surface of another object is called sliding friction force.
(2) the experiment to study the relationship between the size of sliding friction force and which factors: why do we use the spring scale to pull the wood block to do uniform linear motion in the experiment? This is because the spring scale measures the tensile force, not the friction force. When the wood block moves in a straight line at a uniform speed, the horizontal tensile force of the wood block and the friction force of the board against the wood block are a pair of balance forces. According to the condition of the balance of the two forces, the tensile force should be equal to the friction force. Therefore, measuring the tensile force is also measuring the friction force, The greater the pressure is, the greater the sliding friction is; The coarser the contact surface is, the greater the sliding friction is.
(3) the sliding friction is the force that hinders the relative motion of objects in contact with each other, not necessarily the force that hinders the motion of objects, It should be clear that the object in contact with each other is used as the reference to hinder the "relative motion". The "object motion" may use other objects as the reference. For example, in the experiment, when a weight is placed on the wood block and the spring scale is used to pull the wood block to move at a uniform speed in a straight line, The specific situation is: when the wood block is pulled forward from static, the weight will slide backward relative to the wood block, and the wood block will give the weight a friction force to prevent it from sliding backward. The direction of the friction force is forward. Therefore, the weight does not slide relative to the wood block, In this case, the friction is static friction.
(4) the sliding friction has nothing to do with the speed of the motion of the object, and has nothing to do with the size of the contact area between objects.
(5) in order to simplify the practical problems, we often use the "idealized" method, such as one object is placed on the smooth surface of another object, which means that if two objects move relative to each other, the "smooth" method is used, There is no friction between them.
3. Static friction is proced by the interaction of two mutually stationary objects. The direction of static friction can be the same as or opposite to the direction of force.
4, Due to the deformation of two objects in contact, the rolling friction is called rolling friction
where n is the pressure, and N = mg
u is the sliding friction coefficient on the horizontal ground, which is related to the material.
friction
1, friction
(1) definition: when two objects in contact with each other are about to move or have moved relative to each other, they will proce a force on the contact surface to hinder the relative movement, This kind of force is called friction.
(2) the friction between objects must have the following three conditions:
first, the objects contact and squeeze each other
Second, the contact surface is not smooth
Third, there is a relative movement trend or relative movement between objects.
2 Sliding friction force
(1) definition: the friction force generated when an object slides on the surface of another object is called sliding friction force.
(2) the experiment to study the relationship between the size of sliding friction force and which factors: why do we use the spring scale to pull the wood block to do uniform linear motion in the experiment? This is because the spring scale measures the tensile force, not the friction force. When the wood block moves in a straight line at a uniform speed, the horizontal tensile force of the wood block and the friction force of the board against the wood block are a pair of balance forces. According to the condition of the balance of the two forces, the tensile force should be equal to the friction force. Therefore, measuring the tensile force is also measuring the friction force, The greater the pressure is, the greater the sliding friction is; The coarser the contact surface is, the greater the sliding friction is.
(3) the sliding friction is the force that hinders the relative motion of objects in contact with each other, not necessarily the force that hinders the motion of objects, It should be clear that the object in contact with each other is used as the reference to hinder the "relative motion". The "object motion" may use other objects as the reference. For example, in the experiment, when a weight is placed on the wood block and the spring scale is used to pull the wood block to move at a uniform speed in a straight line, The specific situation is: when the wood block is pulled forward from static, the weight will slide backward relative to the wood block, and the wood block will give the weight a friction force to prevent it from sliding backward. The direction of the friction force is forward. Therefore, the weight does not slide relative to the wood block, In this case, the friction is static friction.
(4) the sliding friction has nothing to do with the speed of the motion of the object, and has nothing to do with the size of the contact area between objects.
(5) in order to simplify the practical problems, we often use the "idealized" method, such as one object is placed on the smooth surface of another object, which means that if two objects move relative to each other, the "smooth" method is used, There is no friction between them.
3. Static friction is proced by the interaction of two mutually stationary objects. The direction of static friction can be the same as or opposite to the direction of force.
4, Due to the deformation of two objects in contact, the rolling friction is called rolling friction
3. The calculation method of sliding friction is different from that of static friction. When solving the friction, we must distinguish static friction from sliding friction.
I. calculation of sliding friction
1= μ FN calculation.
(1) according to the force condition of the object, calculate the positive pressure FN.
(2) according to the formula F= μ 2. Two force balance method: the object is in the state of equilibrium (uniform velocity, static positive), according to the two force balance conditions to solve; 2、 Calculation of static friction force
1. Balance condition method is used to solve static friction force. As shown in Fig. 3-3-19, a static object is placed on the horizontal plane. When a person pushes the object with horizontal thrust, the object is still. According to the two force balance condition, the static friction force is equal to the thrust force,
2, The value range of static friction is O & lt; F ≤ Fmax is independent of the positive pressure between objects, so the formula F cannot be used= μ FN solution.
3. Maximum static friction Fmax The value is equal to the external force along the contact surface when the object is just sliding, which is the maximum value of static friction and greater than sliding friction. Generally speaking, they are equal, and the maximum static friction is Fmax.. The formula is Fmax= μ Static FN, μ Static is the static friction coefficient and specific dynamic friction coefficient between objects μ Slightly larger
I. calculation of sliding friction
1= μ FN calculation.
(1) according to the force condition of the object, calculate the positive pressure FN.
(2) according to the formula F= μ 2. Two force balance method: the object is in the state of equilibrium (uniform velocity, static positive), according to the two force balance conditions to solve; 2、 Calculation of static friction force
1. Balance condition method is used to solve static friction force. As shown in Fig. 3-3-19, a static object is placed on the horizontal plane. When a person pushes the object with horizontal thrust, the object is still. According to the two force balance condition, the static friction force is equal to the thrust force,
2, The value range of static friction is O & lt; F ≤ Fmax is independent of the positive pressure between objects, so the formula F cannot be used= μ FN solution.
3. Maximum static friction Fmax The value is equal to the external force along the contact surface when the object is just sliding, which is the maximum value of static friction and greater than sliding friction. Generally speaking, they are equal, and the maximum static friction is Fmax.. The formula is Fmax= μ Static FN, μ Static is the static friction coefficient and specific dynamic friction coefficient between objects μ Slightly larger
4. In the case of lucky money, cash withdrawal is not allowed.
5.
Calculation formula F of sliding friction= μ N Where f is the sliding friction, μ It's the coefficient of sliding friction, and N is the positive pressure between two objects. It's not hard to see that the coefficient of friction μ The larger the positive pressure is, the greater the sliding friction is
(1) in the force analysis of the object, we must first analyze the elastic force, and then analyze the sliding friction. In general, the method of orthogonal decomposition of coordinate system is adopted in force analysis
(2) if there is sliding friction, the formula F can be used= μ N. Where n is the positive pressure, not necessarily equal to the object's gravity mg Thedefinition method is the most basic method to judge the direction of friction, which is true for both static friction and sliding friction
when two objects in contact with each other make relative motion or have the tendency of relative motion, a force that hinders the relative motion or the tendency of relative motion will be generated on the contact surface, which is called friction. From the definition of friction, the direction of friction is to hinder the relative movement direction or relative movement trend (direction)
In many cases, for physics problems, it will involve the identification of friction properties; In other words, the known conditions in the title can not directly determine whether the friction is sliding or static At this time, the first step to solve the problem is to determine the nature of frictionin judging the nature of friction, first of all, it is assumed that the static friction is the whole, and the acceleration of the whole is calculated. When using the maximum static friction (sliding friction) of a single object (usually the object subject to friction only) to determine whether this acceleration can be provided
1, if it is possible, it is assumed that there is static friction between them
If the hypothesis does not hold, it must be sliding friction6. When on flat ground= μ Mg, on the slope f = μ Mgcosa (a is the inclined angle of the object on the inclined plane)
if the pressure is equal to gravity plus other forces, then f = μ Mg + F), and F is the other force. In a word, the sliding friction is equal to the coefficient of friction multiplied by the supporting force (that is, the pressure on other objects is only small in calculation), and the pressure on other objects can be the resultant force of multiple forces
if the pressure is equal to gravity plus other forces, then f = μ Mg + F), and F is the other force. In a word, the sliding friction is equal to the coefficient of friction multiplied by the supporting force (that is, the pressure on other objects is only small in calculation), and the pressure on other objects can be the resultant force of multiple forces
7. First of all, variable speed or constant speed has no effect on sliding friction, or F= μ N
8. How to calculate the friction force
two force balance or pressure multiplied by sliding friction coefficient
the calculation formula of sliding friction force is f= μ N. In the formula μ Dynamic friction coefficient, also called sliding friction coefficient, is only related to material and roughness of contact surface, but has nothing to do with contact area; N is the positive pressure.
two force balance or pressure multiplied by sliding friction coefficient
the calculation formula of sliding friction force is f= μ N. In the formula μ Dynamic friction coefficient, also called sliding friction coefficient, is only related to material and roughness of contact surface, but has nothing to do with contact area; N is the positive pressure.
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