How to calculate the friction in junior high school
Publish: 2021-04-19 23:05:11
1. You can't withdraw money, can you? help
2. Friction refers to the force that hinders the relative motion (or relative motion trend) of an object. Its direction is opposite to the relative motion (or relative motion trend) of the object. Friction is divided into static friction, rolling friction and sliding friction. The sliding friction is related to the roughness of the contact surface and the pressure. The larger the pressure is, the rougher the contact surface is, and the greater the sliding friction is
friction is related to objects that rub against each other, so the description of friction in physics is not general, nor is it as accurate as other forces. Without friction, shoelaces can't be fastened, and screws and nails can't hold objects
the biggest difference in friction is between static friction and other friction. Some people think that static friction should not actually be counted as friction. Other frictional forces are related to dissipation: it reces the relative velocity of objects that rub against each other and converts mechanical energy into heat energy< The friction between solid surfaces can be divided into sliding friction, rolling friction, static friction, rolling friction and rotational friction. In engineering technology, people use lubricating oil to rece friction. If two surfaces are separated by a layer of liquid, liquid friction can occur between them. If the separation of liquid is not complete, mixed friction may also occur. Air track works by air friction. The working principle of lubricating oil and air track is to use "liquid or gas (i.e. fluid) friction to replace solid friction" to work
If lubricating oil, liquid or gas flows along a solid surface, its velocity will be reced e to the influence of friction. The structure of the solid surface has little effect on the friction, and the most important one is the cross-sectional area of the fluid. The reason is that there is friction not only at the interface between the fluid and the solid, but also between different layers in the fluid, and the velocity of the fluid varies with the distance from the solid surface
an object moving relative to a fluid is resisted. This resistance is in the opposite direction of its motion. In the case of laminar flow, the resistance is proportional to its velocity. In turbulence, the resistance is proportional to the square of its velocity. Sometimes an object is subject to resistance and friction at the same time. For example, when a car is moving, it is subject to the resistance of air and the rolling friction of its tires Friction sometimes makes objects move, unlike resistance.)
friction is related to objects that rub against each other, so the description of friction in physics is not general, nor is it as accurate as other forces. Without friction, shoelaces can't be fastened, and screws and nails can't hold objects
the biggest difference in friction is between static friction and other friction. Some people think that static friction should not actually be counted as friction. Other frictional forces are related to dissipation: it reces the relative velocity of objects that rub against each other and converts mechanical energy into heat energy< The friction between solid surfaces can be divided into sliding friction, rolling friction, static friction, rolling friction and rotational friction. In engineering technology, people use lubricating oil to rece friction. If two surfaces are separated by a layer of liquid, liquid friction can occur between them. If the separation of liquid is not complete, mixed friction may also occur. Air track works by air friction. The working principle of lubricating oil and air track is to use "liquid or gas (i.e. fluid) friction to replace solid friction" to work
If lubricating oil, liquid or gas flows along a solid surface, its velocity will be reced e to the influence of friction. The structure of the solid surface has little effect on the friction, and the most important one is the cross-sectional area of the fluid. The reason is that there is friction not only at the interface between the fluid and the solid, but also between different layers in the fluid, and the velocity of the fluid varies with the distance from the solid surface
an object moving relative to a fluid is resisted. This resistance is in the opposite direction of its motion. In the case of laminar flow, the resistance is proportional to its velocity. In turbulence, the resistance is proportional to the square of its velocity. Sometimes an object is subject to resistance and friction at the same time. For example, when a car is moving, it is subject to the resistance of air and the rolling friction of its tires Friction sometimes makes objects move, unlike resistance.)
3. According to Newton's second law, the resultant force is equal to the mass times the acceleration
4. In junior high school, the friction force is generally analyzed according to the motion state (static or uniform linear motion), and the friction force is obtained according to the force balance.
5. When calculating the size of friction, we should first judge whether the friction is sliding friction or static friction. And then it is solved by the corresponding method
the calculation formula of sliding friction 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
sliding friction: the force that occurs between two objects that contact each other and slide relatively, and prevents them from sliding relatively
the direction of friction is opposite to the direction of relative motion or the trend of relative motion. Instead of moving in the opposite direction of the object. Friction can be used as power or resistance.
the calculation formula of sliding friction 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
sliding friction: the force that occurs between two objects that contact each other and slide relatively, and prevents them from sliding relatively
the direction of friction is opposite to the direction of relative motion or the trend of relative motion. Instead of moving in the opposite direction of the object. Friction can be used as power or resistance.
6. Friction is related to three factors: 1. Positive pressure; 2. Friction coefficient between contact surfaces; 3. There is a trend of relative motion between two objects.
there is no direct relationship between friction and gravity. Gravity of an object in a horizontal plane is equivalent to positive pressure. In this case, as long as the contact surface is not smooth, there is a dynamic friction coefficient, and there is a trend of relative motion between the object and the horizontal plane, We can use the formula: friction = friction coefficient * positive pressure (gravity)
however, the calculation method of friction on the inclined plane is different, and it is also related to the inclination angle of the inclined plane. When the object is placed on the inclined plane and at rest, it can be used as follows: friction = gravity * sin (inclination)
if the object is sliding on the inclined plane, then friction = friction coefficient * gravity * cos (inclination)
the pulling force of pulling the object at a constant speed is not necessarily friction. If the pulling force is in a straight line with the moving direction of the object, it can be said that the pulling force is equal to the friction, If it is not in a straight line, the component of the pulling force in the moving direction of the object should be used as the size of the friction force.
there is no direct relationship between friction and gravity. Gravity of an object in a horizontal plane is equivalent to positive pressure. In this case, as long as the contact surface is not smooth, there is a dynamic friction coefficient, and there is a trend of relative motion between the object and the horizontal plane, We can use the formula: friction = friction coefficient * positive pressure (gravity)
however, the calculation method of friction on the inclined plane is different, and it is also related to the inclination angle of the inclined plane. When the object is placed on the inclined plane and at rest, it can be used as follows: friction = gravity * sin (inclination)
if the object is sliding on the inclined plane, then friction = friction coefficient * gravity * cos (inclination)
the pulling force of pulling the object at a constant speed is not necessarily friction. If the pulling force is in a straight line with the moving direction of the object, it can be said that the pulling force is equal to the friction, If it is not in a straight line, the component of the pulling force in the moving direction of the object should be used as the size of the friction force.
7. The wooden box is not subject to friction, because both the car and the wooden box move in a straight line at a constant speed to the right, and the force in the horizontal direction must be balanced. If the wooden box is subject to friction, no matter which direction, its motion will not be uniform, because there is no second force to balance the friction. In conclusion, the wooden box is not subject to friction... The above is mechanical stress analysis in Senior High School... It may not be easy for junior high school to learn acceleration
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