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# What is static friction?

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Static friction is the resistance to movement when two non-moving solid objects are in contact with each other. Static friction matches applied force and prevents motion. When the applied force overcomes static friction, the object starts moving, and at this point, static friction ceases and kinetic friction comes into play.

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Static friction is what keeps an object stationary when it is placed on a surface. It is, for example, what keeps a wooden block from sliding down a small incline. Static friction varies based on the force applied to the object, but has a maximum value. This is calculated by multiplying the coefficient of static friction by the normal force (the force applied perpendicular to the object).

The coefficient of static friction itself varies depending on the pair of materials in contact and is measured based on the angle of inclination at which motion just starts to occur. In general, rough objects tend to have higher coefficients of static friction. Lubrication often lowers the coefficient of static friction of a pair of materials. For example, The coefficient of static friction between dry concrete and rubber is 1.0 but decreases to 0.30 when wet, resulting in a more slippery surface.

Rolling friction occurs when one object rolls across the other. However, since both objects are stationary relative to each other at the point of contact, this is classified under static friction.

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## Related Questions

• A:

Since friction opposes movement, it causes resistance that makes it harder for a sliding object to move, thus slowing down movement. Friction can be seen through the example of a car making a stop; the wheels and breaks cause friction, making the car slow down. In addition to affecting solid objects, friction also causes resistance with glass and liquids by causing a collision that results in heat.

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One can explain friction to a child by using real-world examples of situations the child has experienced, such as movement, stopping, sliding and slowing down. Physics4Kids defines friction as a force that acts in an opposite direction to movement. A car slows down at a stop sign because of the friction between the brakes and the wheels as they rub against each other.

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Friction is a force that tends to stop motion or resist the motion of objects. Friction is always a negative force, which means it acts in a direction opposite to the direction of the force applied to the object. Movement of objects through air and liquids gives rise to friction.