الاحتكاك وقوانين نيوتن (تم تعديل العنوان) [الأرشيف]

nouf jmela

07-12-2010, 22:37

Friction
The friction force applied in the opposite direction to the speed of the body. In the case of dry sliding friction where there is no lubrication or lubrication, the friction force almost independent of speed. The friction force does not depend on contact area between the body and the surface sliding it. The actual contact area is relatively small area, known as the friction that region where there is physical contact between each of the small bumps on the surface of the body and dumped it.
During the movement of the body sliding on the surface, they collide with each of the small bumps on it and that surface, and then the force will be required to take the bumps next to each other. And the actual contact area depends on the normal force between the body and the slider surface. This is equivalent to the force often sliding body weight completely. However, if the payment of a horizontal body angle, the vertical downward component to the bottom of the force will add to the weight of the body. And proportionate to the force with the total frictional force helicopter.
In the fourth century AH / tenth century between Ibn Sina that perpetual motion is impossible, noted that the resistance of the medium in which the body moves which lead to the repeal movement as it says in his book signals and alerts: "No one shall be a body of objects in a natural force that moves the body without end ... If it is said that he could, the rights for example, may move his hand or some of its parts, which does not move from place to place, what do you see how the hand to be the case, you may be moving and not go from place to place, as well as the rule of thumb is may be moving and moving from place to place, and runs along the other a second time?. I know that it is moved over the body has moved the sentence, and when it moved that sentence has moved those parts, because those parts are not that sentence. so that if action rights has moved among its members; and its members have moved if he moved; but only moved his hand and has moved all parts of the hand, because the hand is not something other than those parts, as well as the movement of one finger has moved a finger parts of all, because fingers are not those parts, it is thought that may be moving parts and do not move the sentence, or move the sentence and do not move some parts of it wrong. "
When there is power, it will become the second law of movement as follows:
S effective - friction s = k c
Represents the left side of the equation is simply the net effective force. (It will be fixed wheel in the direction of effective force). However, when he moves the body through the liquid, the size will depend on the friction speed. For most of the objects of a size as big as rights, which are moving in the water or air (less quickly than the speed of light), the resulting friction will be proportional to the square of speed. Thus, it becomes the second law of movement as follows:
S effective - w n 2 = k c
The constant of proportionality of the attributes of the articles which sliding closer after each other, and this constant depends on the contact area between the sliding surfaces and the degree of a moving object
Friction is the force and resistance, which occurs when two surfaces move in opposite directions in close proximity to each other when the force pressing on Tlahmanma working together (weight Sun objects for example). And produce a quantity of heat.
Friction occurs between solids, liquid and gas or any combination of them.
The friction force is multiplied by the power required between objects in the coefficient of friction. Right = Qd X μ where: right: the power of friction Qd: the power required between the objects or the force perpendicular to the surface of the separation between μ: coefficient of friction, either static (μ s) or kinetic (μ h)
The friction force applied in the opposite direction to the speed of the body. For example, if the payment of a chair on the ground to the right, the force of friction, heading to the left. Created friction force between objects by the presence of bumps and gaps between surfaces, the larger the smooth surfaces, the less that force. During the movement of the body surface, they collide with each of the small bumps on it and that surface, and then the force will be required to take the bumps next to each other. And the actual contact area depends on the normal force between the body and the slider surface. And proportionate to the force with the total frictional force and vertical force equivalent to the body weight often slide completely. And in the case of dry sliding friction where there is no lubrication or lubrication, the friction force almost independent of speed. The friction force does not depend on contact area between the body and the surface sliding it. The actual contact area is relatively small area, known as the friction that region where there is physical contact between each of the small bumps on the surface of the body and dumped it.
Coefficient of friction
Coefficient of friction is a numerical quantity used to express the ratio between the friction force between two objects and the power required between them, and no unit of measurement. Depends on the subjects and objects. For example, ice on the metal are low coefficient of friction (ie, they Inzleghan some easily). As they had the rubber on asphalt coefficient of friction is too high (not Inzleghan to some), see table. μ X 2 surface ice surface 1 0.06 Wood 0.02 - 0.1 Snow 0.07 brass metal (lubricated) Metal 0.25 oak wood oak wood 0.5 - 0.9 Concrete (wet) Rubber 0.7 - 1 Rubber Concrete dry static coefficient of friction of some materials
The coefficient of friction is the amount of experimental, which means that he must be measured by experiment and can be calculated by mathematical equations. Most of the dry material with each factor gives the friction between 0.3 and 0.6. It is difficult to get the value out of this area. The value of 0 for the coefficient of friction means that there is no friction at all, and slide objects on each other to no end. And the coefficient of static friction is greater than motor mounts and because the gaps between adjacent surfaces of objects overlap each other in Vzbban resistance of the sliding surfaces. But if the body began to slide it will not have time to two surfaces in order to Itlahama fully with each other.
Types of friction
Static friction
Static friction occurs when objects not Trcan for each other (such as the table on the ground). Static coefficient of friction that has the symbol (μ o). Primary force necessary to move this body are usually slightly larger than the static friction force. Static friction coefficient is usually larger than the kinetic coefficient of friction.
An example of static friction is the force that prevents the tires from slipping on the surface of rotation. Although the wheels spin, but the point of relative movement between the wheel and the earth shall be static for the land, so it's not static friction Tharikia.
Kinetic friction
Kinetic friction occurs when objects move in relation to each other and come into contact with each other (such as Ps manipulations on the ground). Kinetic coefficient of friction that has the symbol (μ h). And is usually less than static coefficient of friction.
Examples of kinetic friction
• sliding friction: occurs when two objects come into contact with each other hard disks (such as moving a book on the table).
• fluid friction (fluid friction): occurs when a solid object moving through a liquid or gas (such as air resistance to the movement of the aircraft, or water resistant diver's movement).
Energy lost due to friction: When the body moves on the surface by a factor of kinetic friction (μ h) and vertical force (Qa) The amount of energy lost due to friction is equal to U: U = μ h Qa X X P, where P is the distance made by the body. This equation similar to equation (energy lost = force X distance) and this is because the amount of friction is headed.
The benefits of friction
Often look to the force of friction as a force-consuming, and interfere with the movement of objects, and when we calculate work done against friction we consider whom have lost and are trying in many of the mechanical design to reduce friction forces to the lowest possible in order to achieve better performance of the equipment, but .. Does friction detrimental to this point? What would happen if the moment of friction in what has disappeared from the world, which became a zero?
If there is no friction disappeared must train and car and all means of transportation will not be able to move because they move by friction between the ground and the wheels. Even if they are moved will not be able to stop, because the brakes depends mainly on the friction. The people can not walk or even stand and pause sound, as if they are standing on the floor of ice. And will not be able to do anything to storytelling that slip from their hands. As Stft mountains and will not stay in any cover of the soil. And will not remain intact, but any building will collapse. And Stvk ropes tied. All this because of the lack of slip and friction. In short, life is impossible without friction.
Vllaankak important benefits; it makes the wheels of the vehicle moving on the sidewalk, and makes the wheels of the locomotive stuck rods railways. It allows to move the carrier that runs the roller without slippage. And you can not walk without friction to prevent your shoes from skating on the sidewalk. Therefore, it is difficult to walk on ice; as the smooth surface causes less friction from the pavement, thus allowing for the shoes to slip. And proven soil on the surface of the mountains and buildings and prove it in place. And makes the ropes tied to remain constant. In addition to dozens if not hundreds of other benefits.
Disadvantages of friction
Despite the importance of friction and the impossibility of life without him as we have seen, but it has several disadvantages that could lead to significant damage in the long run. Work done by friction is converted to heat and deformation. In machinery, makes contact with a large part of the energy expended in vain. And turning it into heat requires more cooling. And sometimes causes friction to melt some of the objects also leads to distortion, and distortion in the status of objects acquired with friction. Though it may be useful in some cases (such as refinement of objects). But it wont be a problem, because the objects they wear and lose their ability to endure, and may break down some of the machines. And in the long run can affect the properties of surfaces and may affect the coefficient of friction itself, and you can see this yourself in old tires, where the surface is completely smooth. These are the disadvantages of friction in practical life. And has been and continues to have a negative impact of friction in the development of science, has been delayed conclusion of the laws of motion for many years because of friction. And because the heat and movement generated by the friction dissipated quickly, it was concluded many of the ancient philosophers (and among them Aristotle) that moving objects lose energy without the presence of the opposite to them. This theory wrong and were not to be formulated without friction.
Ways of reducing the friction
• Hardware:
Such as rotating wheels or tubes used in airports to transfer bags from one place to another. Which turns friction to sliding friction Dhrouje. , Which reduces friction.
• Techniques:
One of the techniques used by engineers trains is to make the links between the trailers, train loose. And so the train can be withdrawn each trailer separately, instead of withdrawing them all. This reduces friction and makes the overall distributed over time.
• lubricants or lubricating fluids:
Of the most important means used to reduce friction is to use lubricants, such as oils and grease. Valzi reduces friction. Vamaaml friction of iron on the ongoing operation oiled wood, for example, becomes much less than 0,018, because the type of surface has no effect when it is almost covered with oil or other fluids, and then the friction depends on the viscosity of the liquid and the relative speed between the moving surfaces. With most lubricants are liquid, but some such as the heart of talc and graphite.
And liquid lubricants be "sticky" Low placed between two surfaces to reduce the coefficient of friction significantly. Nice and fluid less viscous liquids, the large intestine, and a faster flow. Vallzojp characteristic properties make them resistant to fluid flow. They occur as a result of the internal friction of the liquid molecules, which move off each other. Valmaia with a low viscosity (eg soap), pouring more rapidly than the fluid with high viscosity (glue for example).
For all fluids, including liquids, and gases, a certain degree of viscosity. Some of the material that looks like solid materials with high viscosity and flow very slowly, for example, bitumen. And the degree of viscosity is very important in many applications. For example, determine the viscosity of engine oil lubrication efficiency in parts of the engine. The greater the overlap of the liquid molecules more powerful, the viscosity of the liquid greater. In general, whenever the size or length of the molecule, the greater is the overlap is stronger. And determine the temperature of the fluid force molecules overlap, where overlap of molecules in the fluid over the lower temperature. Thus, the hot fluid be less than the viscosity of the viscosity of fluids cold. But the gas molecules interfere more strongly at high temperature. Therefore, it is greater than the viscosity of the viscosity of cold gas. One way to increase the viscosity of a liquid is a polymer melt (long molecular chains) in it. These molecules and become intertwined Vtquaom flow. Also, the addition of solid particles of the fluid also increases the degree of viscosity [2].
Cold fusion
With, the greater the roughness increased friction. But if you put two surfaces so smooth (close to the full smoothness) of the metal with some impurities and removed them completely by the vacuum, they Siltsqan with some and it becomes difficult to separate them and is so-called "cold fusion". This means that when the body close to the stage full of smoothness. Becomes dependent on the nature of friction forces in the area of molecular docking. Therefore, the various objects that have the same degree of smoothness may have very different coefficients of friction.

Sources

1. Translate the English version adapted
2. Adapted from one of the themes and Healing Network
3. Friction
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