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proportionality constant, friction force, velocity, magnitude, equation

Friction acts like a force applied in the direction opposite to an object’s velocity. For dry sliding friction, where no lubrication is present, the friction force is almost independent of velocity. Also, the friction force does not depend on the apparent area of contact between an object and the surface upon which it slides. The actual contact area—that is, the area where the microscopic bumps on the object and sliding surface are actually touching each other—is relatively small. As the object moves across the sliding surface, the tiny bumps on the object and sliding surface collide, and force is required to move the bumps past each other. The actual contact area depends on the perpendicular force between the object and sliding surface. Frequently this force is just the weight of the sliding object. If the object is pushed at an angle to the horizontal, however, the downward vertical component of the force will, in effect, add to the weight of the object. The friction force is proportional to the total perpendicular force.

The left side of the equation is simply the net effective force. (Acceleration will be constant in the direction of the effective force). When an object moves through a liquid, however, the magnitude of the friction depends on the velocity. For most human-size objects moving in water or air (at subsonic speeds).

The proportionality constant, k, is characteristic of the two materials that are sliding past each other, and depends on the area of contact between the two surfaces and the degree of streamlining of the moving object.

Article key phrases:

proportionality constant, friction force, velocity, magnitude, equation, Acceleration, friction, characteristic, lubrication, angle, effect, direction, liquid, surfaces, water, weight, air, materials

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