The coefficient of static friction is a numerical value that determines the force required to initiate motion between two objects. It varies with the materials they are made of and is symbolized by the Greek letter “mu”. The lower the coefficient, the more slippery the surfaces are. When the gravitational force is greater than the coefficient of static friction, the system becomes kinetic.
The coefficient of static friction is a number determined based on the static forces of two objects, typically influenced by electromagnetic forces determined by the materials the objects are made of. It is a value used in static systems where two or more objects are at rest together, and is an indication of the force that will be required to get one of the objects to start moving. The coefficient of static friction is typically symbolized with the Greek letter “mu” and is different according to the materials from which the objects can be made.
Also called the coefficient of static friction or coefficient of static friction, the coefficient of static friction is a numerical value that can be determined for objects made of various materials. In general, it is a relationship determined by establishing the force required to produce movement or sliding between two objects, and the normal force exerted between the two objects. The force required to initiate motion when divided by the normal force will yield a numerical value, which is the coefficient of static friction for those objects or the materials they are made of. In a system at rest, such as a block of wood lying on a wooden plank, the normal force equals the force of gravity and prevents the block from entering the plank.
The lower the coefficient of static friction for a pair of objects and the materials they are made of, the more slippery these surfaces are together and the easier it will be for movement between surfaces to initiate. For example, the block of wood on top of a wooden board has a static coefficient of friction between 0.25 and 0.5, which is quite low. Teflon, one of the slipperiest materials available, has a coefficient of static friction with most other materials of about 0.04.
Rubber on dry concrete has a coefficient of static friction of about 1.0 which allows a car’s tires to grip the road and bring the car to a stop. Since one end of the aforementioned wooden plank is raised slightly, creating a slope, the wooden block will initially remain stationary and the system remains static. This is because the force pulling the block of wood down the slope is not yet sufficient to overcome the static friction between the two wooden surfaces.
At a certain angle, however, gravity is great enough to overcome the frictional force between the two objects, and the block of wood begins to slide along the board. The gravitational force required to move the block of wood on the board must be greater than the coefficient of static friction, times the mass of the block times the normal force. When an object is not tilted, the normal force is equal to the gravitational force or the weight of the object, but as the angle increases the normal force decreases and with the correct angle it is no longer large enough to keep the system static . At that point, motion begins and the frictional force becomes kinetic friction, rather than static friction.
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