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The difference between kinetic and static friction can be understood by looking at when each type of force acts. Static friction works on objects that are not moving. It prevents motion by holding the object in place, even when a force is applied. For instance, when you try to push a parked car and it doesn't move, static friction is resisting the push. This friction changes in strength depending on how much force you apply, up to a certain maximum. Kinetic friction acts only after the object begins to slide. Once motion starts, static friction disappears and kinetic friction takes over. This type of friction remains constant while the object is moving. It is usually weaker than static friction, which is why it takes less effort to keep something moving than to start it. A sliding book on a table or a sled on snow are common examples.
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