How to calculate the circle friction
Publish: 2021-05-11 19:40:14
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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. When calculating the size of friction, we should first judge whether the friction is sliding friction or static friction, and then use the corresponding method to find out.
the formula for calculating the size of sliding friction is f= μ N, where 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.
sliding friction: the force that occurs between two objects that contact each other and slide relative to each other, and prevents them from sliding relative to each other.
the direction of friction is opposite to the direction of relative motion or the direction of relative motion trend of the object, but not opposite to the direction of motion of the object. Friction can be used as power or resistance
the formula for calculating the size of sliding friction is f= μ N, where 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.
sliding friction: the force that occurs between two objects that contact each other and slide relative to each other, and prevents them from sliding relative to each other.
the direction of friction is opposite to the direction of relative motion or the direction of relative motion trend of the object, but not opposite to the direction of motion of the object. Friction can be used as power or resistance
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8. 1. Friction force
(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 kind of force on the contact surface that hinders the movement of each other. This force is called friction force.
(2) the following three conditions must be met to proce friction force between objects:
first, the mutual contact between objects Extrusion
Second, the contact surface is not smooth
Third, there is a relative motion trend or relative motion between objects.
(3) the concept of friction should be understood clearly.
first, friction is possible when two objects contact each other, Second, friction occurs in pairs. When a and B are in contact and have a relative movement trend or have a relative movement, a has a friction effect on B, Third, there are two kinds of friction: static friction and dynamic friction. There is a tendency of relative motion when two objects contact, but there is no relative motion. In this case, the friction is called static friction, Fourth, the relative motion of objects in contact may be sliding or rolling, so the friction may be sliding friction or rolling friction.
fifth, there is a relative motion tendency between objects, which means that objects are in the state of moving but not moving, and at this time objects are still relatively static, So we can't
think that a static object will not be subject to friction; On the contrary, a moving object is not necessarily affected by friction. For example, objects a and B are stacked together
moving along the horizontal plane at the same speed in a straight line with uniform speed. Although both objects are moving, there is no relative motion between them because the speed and direction of objects a and B are the same, So there is no friction force between two objects.
2. Sliding friction force
(1) definition: when one object slides on the surface of another object, the friction force is called sliding friction force.
(2) experiments to study the relationship between the size of sliding friction force and which factors:
Why do we use a spring scale to pull wood blocks to move in a uniform straight line? This is because the spring scale measures the tensile force, not the friction force, which is large
small, The tensile force should be equal to the friction force, so measuring the tensile force means measuring the friction force.
a large number of experiments show that the sliding friction force is only related to the pressure and the roughness of the contact surface; The coarser the contact surface is, the greater the sliding friction is.
(3) 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 "relative motion" is hindered by objects in contact with each other as reference objects. "Object
Motion" may be based on other objects as reference objects. 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 for uniform linear motion
, The specific situation is: when the wooden block is pulled forward by the pulling force
from static, the weight will slide backward relative to the wooden block, and the wooden block will give the weight a friction to prevent it from sliding backward, The direction of the friction is forward, so the weight does not slide relative to the wood block, and the friction is static friction.
(4) the sliding friction has nothing to do with the speed of the movement of the object, and has nothing to do with the size of the contact area between the objects.
(5) in order to simplify the practical problems, the "idealized" method is often used, If an object is placed on the smooth surface of another object, this means that there is no friction between two objects when they move relative to each other.
3. Methods to increase beneficial friction
(1) increase the pressure on the contact surface, Bicycles are easy to stop.
(2) rough the contact surface. For example, the uneven tread patterns on the tires of automobiles, tractors and bicycles are designed to increase the roughness of the contact surface, so as to increase the friction between the tire and the ground.
(3) in addition to the above two methods to increase the beneficial friction, The method of changing rolling to sliding can also be used to increase the beneficial friction. For example, when the train or car is in emergency braking, the wheel only slides but does not roll, and the car stops quickly.
4. Methods of recing harmful friction.
(1) recing the pressure on the contact surface.
(2) recing the roughness of the contact surface.
(3) using rolling instead of sliding, The rolling friction is much smaller than sliding friction. For example, there are many smooth steel balls or steel columns between the inner and outer rings of the bearing. When the wheel rotates, it drives the outer ring to rotate, and the steel balls or steel columns roll between the inner and outer rings, so the friction is greatly reced, (5) using compressed gas to form a layer of air cushion between the friction surfaces to make the friction surface out of contact, which can make the friction smaller. For example, hovercraft. 2, Why 2) After pushing the wooden box on the horizontal ground, the students have to continue to push hard to keep it moving in a uniform and straight line. Why 3) Why did the students push the desk hard but fail to move 4) When a piece of wood is placed on an inclined plane with rough surface, why does it not slide down but rest on the inclined plane
tips and instructions:
(1) after skaters stop exerting at the end of skating, because there is friction between the skate and the ice, skaters will slowly
stop 2) When the wooden box moves, it is subject to the friction between the bottom of the box and the ground. In order to keep the wooden box moving at a uniform speed and in a straight line, there must be a thrust that is balanced with the friction
force, so it is necessary to continue to push hard 3) Because the friction between the desk and the ground is balanced with the thrust of the students
(4) there is friction between the block and the rough slope
(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 kind of force on the contact surface that hinders the movement of each other. This force is called friction force.
(2) the following three conditions must be met to proce friction force between objects:
first, the mutual contact between objects Extrusion
Second, the contact surface is not smooth
Third, there is a relative motion trend or relative motion between objects.
(3) the concept of friction should be understood clearly.
first, friction is possible when two objects contact each other, Second, friction occurs in pairs. When a and B are in contact and have a relative movement trend or have a relative movement, a has a friction effect on B, Third, there are two kinds of friction: static friction and dynamic friction. There is a tendency of relative motion when two objects contact, but there is no relative motion. In this case, the friction is called static friction, Fourth, the relative motion of objects in contact may be sliding or rolling, so the friction may be sliding friction or rolling friction.
fifth, there is a relative motion tendency between objects, which means that objects are in the state of moving but not moving, and at this time objects are still relatively static, So we can't
think that a static object will not be subject to friction; On the contrary, a moving object is not necessarily affected by friction. For example, objects a and B are stacked together
moving along the horizontal plane at the same speed in a straight line with uniform speed. Although both objects are moving, there is no relative motion between them because the speed and direction of objects a and B are the same, So there is no friction force between two objects.
2. Sliding friction force
(1) definition: when one object slides on the surface of another object, the friction force is called sliding friction force.
(2) experiments to study the relationship between the size of sliding friction force and which factors:
Why do we use a spring scale to pull wood blocks to move in a uniform straight line? This is because the spring scale measures the tensile force, not the friction force, which is large
small, The tensile force should be equal to the friction force, so measuring the tensile force means measuring the friction force.
a large number of experiments show that the sliding friction force is only related to the pressure and the roughness of the contact surface; The coarser the contact surface is, the greater the sliding friction is.
(3) 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 "relative motion" is hindered by objects in contact with each other as reference objects. "Object
Motion" may be based on other objects as reference objects. 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 for uniform linear motion
, The specific situation is: when the wooden block is pulled forward by the pulling force
from static, the weight will slide backward relative to the wooden block, and the wooden block will give the weight a friction to prevent it from sliding backward, The direction of the friction is forward, so the weight does not slide relative to the wood block, and the friction is static friction.
(4) the sliding friction has nothing to do with the speed of the movement of the object, and has nothing to do with the size of the contact area between the objects.
(5) in order to simplify the practical problems, the "idealized" method is often used, If an object is placed on the smooth surface of another object, this means that there is no friction between two objects when they move relative to each other.
3. Methods to increase beneficial friction
(1) increase the pressure on the contact surface, Bicycles are easy to stop.
(2) rough the contact surface. For example, the uneven tread patterns on the tires of automobiles, tractors and bicycles are designed to increase the roughness of the contact surface, so as to increase the friction between the tire and the ground.
(3) in addition to the above two methods to increase the beneficial friction, The method of changing rolling to sliding can also be used to increase the beneficial friction. For example, when the train or car is in emergency braking, the wheel only slides but does not roll, and the car stops quickly.
4. Methods of recing harmful friction.
(1) recing the pressure on the contact surface.
(2) recing the roughness of the contact surface.
(3) using rolling instead of sliding, The rolling friction is much smaller than sliding friction. For example, there are many smooth steel balls or steel columns between the inner and outer rings of the bearing. When the wheel rotates, it drives the outer ring to rotate, and the steel balls or steel columns roll between the inner and outer rings, so the friction is greatly reced, (5) using compressed gas to form a layer of air cushion between the friction surfaces to make the friction surface out of contact, which can make the friction smaller. For example, hovercraft. 2, Why 2) After pushing the wooden box on the horizontal ground, the students have to continue to push hard to keep it moving in a uniform and straight line. Why 3) Why did the students push the desk hard but fail to move 4) When a piece of wood is placed on an inclined plane with rough surface, why does it not slide down but rest on the inclined plane
tips and instructions:
(1) after skaters stop exerting at the end of skating, because there is friction between the skate and the ice, skaters will slowly
stop 2) When the wooden box moves, it is subject to the friction between the bottom of the box and the ground. In order to keep the wooden box moving at a uniform speed and in a straight line, there must be a thrust that is balanced with the friction
force, so it is necessary to continue to push hard 3) Because the friction between the desk and the ground is balanced with the thrust of the students
(4) there is friction between the block and the rough slope
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