Final answer:
Static friction is the force that prevents motion when an external force is applied, and it must be overcome for movement to start. Kinetic friction is the force experienced by a moving object, which is generally less than static friction, allowing easier continued motion. These principles explain why objects like a book, eraser, or key require more force to start moving than to keep moving.
Step-by-step explanation:
Static and sliding (or kinetic) friction affect the speed of objects such as a paperback book, a flat eraser, and a key by determining the amount of resisting force that must be overcome for the objects to start moving and the force required to keep them moving at a constant speed, respectively. Static friction is the force that keeps objects at rest when a force is applied. It must be overcome to initiate movement. Kinetic friction, on the other hand, occurs once the object is sliding and is usually less than static friction. This difference is noticeable when you push a heavy crate: it requires a greater force to start moving the crate than to keep it sliding due to the higher static friction compared to kinetic friction. Similarly, a paperback book, eraser, and key will experience these types of friction when acted upon by a force. A light object like an eraser with a high coefficient of static friction (μ_s = 0.80) would be more challenging to start moving than keeping it in motion. Once sliding, the frictional force reduces, which is why objects often move more easily once already in motion.
For example, when a chalk screeches across a board, it's because the chalk is rapidly switching between sticking due to static friction and slipping due to kinetic friction. The noise is the result of this rapid transition. Similarly, the initial resistance you feel when trying to slide an object like a key or eraser is static friction at work, and the reduced force needed to keep the object moving is kinetic friction's influence. Overall, these forces are crucial to understanding motion in everyday life.