![]() ![]() If you have a block of brick in your hand and try to slide it on the ground by force then it does not slide that easily, it happens because of frictional force. Because the friction thus far described rises between surfaces in relative motion, it is called kinetic friction. The frictional force is directed oppositely to the motion of the object. ![]() The value of the coefficient of friction for a case of one or more bricks sliding on a clean wooden table is about 0.5, which indicates that a force is equal to half the weight of the bricks is required just to overcome friction in keeping the bricks moving forward with a constant speed. Because both friction and load are calculated in units of force (such as pounds or newtons), the coefficient of friction is dimensionless. This constant ratio is called the coefficient of friction and is typically symbolized by the Greek letter mu (μ). Thus, the ratio of friction F to load L is the same. ![]() If a load of three bricks is pulled along a table, the friction is three times more than if one brick is pulled. Second, friction is directly proportional to the weight that presses the surfaces together. If a brick is pulled along a table, the frictional force is similar whether the brick is lying flat or standing on end. First, the volume of friction is nearly independent of the area of contact. Two basic experimental facts describe the friction of sliding solids. The full amount of friction force that a surface can apply upon an object can be easily measured with the use of the given formula: If an object is pushed against the surface, then the frictional force will be increased and become extra than the weight of the object. (Then positive x corresponds to a stretch and negative x to a compression.If an object is placed against an object, then the frictional force will be the same as the weight of the object. The maximum work is done by a given force when it is along the direction of the displacement (\text=0. As a result, the work done by a force can be positive, negative, or zero, depending on whether the force is generally in the direction of the displacement, generally opposite to the displacement, or perpendicular to the displacement. The components of a vector can be positive, negative, or zero, depending on whether the angle between the vector and the component-direction is between 0^\circ and 90^\circ or 90^\circ and 180^\circ, or is equal to 90^\circ. Recall that the magnitude of a force times the cosine of the angle the force makes with a given direction is the component of the force in the given direction. From the properties of vectors, it doesn’t matter if you take the component of the force parallel to the displacement or the component of the displacement parallel to the force-you get the same result either way. In words, you can express Figure for the work done by a force acting over a displacement as a product of one component acting parallel to the other component. Which choice is more convenient depends on the situation. In two dimensions, these were the x– and y-components in Cartesian coordinates, or the r– and \phi-components in polar coordinates in three dimensions, it was just x-, y-, and z-components. We could equally well have expressed the dot product in terms of the various components introduced in Vectors. We choose to express the dot product in terms of the magnitudes of the vectors and the cosine of the angle between them, because the meaning of the dot product for work can be put into words more directly in terms of magnitudes and angles. ![]()
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