For any given surface, the coefficient of static friction is higher than the coefficient of kinetic friction. More force is required to initally get an object moving than is required to keep it moving. Additionally, static friction only arises in response to an attempt to move an object (overcome the normal force between it and the surface).
A box is resting on a smooth floor. Static friction is present:
only if normal force is present |
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if the coefficient of friction is greater than one |
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at all times |
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when an attempt is made to move the box |