• In this session i am going to explain the topics noted in the previous post
  
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• Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into static friction ("stiction") between non-moving surfaces, and kinetic friction between moving surfaces. 
• Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. 
• Lubricated friction is a case of fluid friction where a lubricate fluid separates two solid surfaces^. 
• Skin friction is a component of drag the force resisting the motion of a fluid across the surface of a body. 
• Internal friction is the force resisting motion between the elements making up a solid material while it undergoes  deformation.
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• Friction is not itself a fundemental force Dry friction arises from a combination of inter-surface adhesion, surface roughness, surface deformation, and surface contamination. 
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•   The elementary property of sliding (kinetic) friction were discovered by experiment in the 15th to 18th centuries and were expressed as three empirical laws: 
• Amontons first law: The force of friction is directly proportional to the applied load.
• Amontons' Second Law: The force of friction is independent of the apparent area of contact.
• Coulomb's Law of Friction: Kinetic friction is independent of the sliding velocity.
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•   Static friction:Static friction is friction between two or more solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction, typically denoted as μ_s, is usually higher than the coefficient of kinetic friction.The maximum value of static friction, when motion is impending, is sometimes referred to as limiting friction, although this term is not used universally. It is also known as traction.
• it can be overcomes through the reverse force applied in the path of the moving object.
•  An example of static friction is the force that prevents a car wheel from slipping as it rolls on the ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction.
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•  Khinetic friction:Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μ_k, and is usually less than the coefficient of static friction for the same materials. However, richard feynman comments that "with dry metals it is very hard to show any difference." The friction force between two surfaces after sliding begins is the product of the coefficient of kinetic friction and the normal force: .
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• Fluid friction: Fluid friction occurs between layers within a fluid that are moving relative to each other. This internal resistance to flow is described as viscosity. In everyday terms viscosity of a fluid is said to have "thickness". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. The less viscous the fluid, the greater its ease of movement. All real fluids (except super fluids) have some resistance to stress and therefore are viscous, but a fluid which has no resistance to shear stress is known as an ideal fluids or inviscid fluid.
   lubrication friction: Lubricated friction is a case of fluid friction where a fluid separates two solid surfaces. Lubrication is a technique employed to reduce wear of one or both surfaces in close proximity moving relative to each another by interposing a substance called a lubricant between the surfaces.
   skin friction: Skin friction arises from the friction of the fluid against the "skin" of the object that is moving through it. Skin friction arises from the interaction between the fluid and the skin of the body, and is directly related to the area of the surface of the body that is in contact with the fluid. Skin friction follows the drag equationand rises with the square of the velocity.
  Skin friction is caused by viscous drag in the boundary layers around the object. There are two ways to decrease skin friction: the first is to shape the moving body so that smooth flow is possible, like an airfoil. The second method is to decrease the length and cross-section of the moving object as much as is practicable.
  Internal friction:Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.
  plastic deformation in solids is an irreversible change in the internal molecular structure of an object. This change may be due to either (or both) an applied force or a change in temperature. The change of an object's shape is called strain. The force causing it is called stress
  Elastic deformation in solids is reversible change in the internal molecular structure of an object. Stress does not necessarily cause permanent change. As deformation occurs, internal forces oppose the applied force. If the applied stress is not too large these opposing forces may completely resist the applied force, allowing the object to assume a new equilibrium state and to return to its original shape when the force is removed. This is known as elastic deformation or elasticity.
  Rolling resistance is the force that resists the rolling of a wheel or other circular object along a surface caused by deformations in the object and/or surface. Generally the force of rolling resistance is less than that associated with kinetic friction. Typical values for the coefficient of rolling resistance are 0.001.One of the most common examples of rolling resistance is the movement of motor vehicle tires on a road, a process which generates heat and sound as by-products.
  triboelectric effect:Rubbing dissimilar materials against one another can cause a build-up of electrostatic charge which can be hazardous if flammable gases or vapors are present. When the static build-up discharges, explosions can be caused by ignition of the flammable mixture.
  belt friction: Belt friction is a physical property observed from the forces acting on a belt wrapped around a pulley, when one end is being pulled. The resulting tension, which acts on both ends of the belt, can be modeled by the belt friction equation.
  In practice, the theoretical tension acting on the belt or rope calculated by the belt friction equation can be compared to the maximum tension the belt can support. This helps a designer of such a rig to know how many times the belt or rope must be wrapped around the pulley to prevent it from slipping. Mountain climbers and sailing crews demonstrate a standard knowledge of belt friction when accomplishing basic tasks.
  
  
  
   some other important topics related friction can be learned in the further posts of superscience.blogspot.com keep going with this blog......................