PTB class 9 chp 3 dynamics sliding friction

Sliding Friction
Sliding friction is the force that opposes the motion of one surface sliding over another surface in contact with it. When an object moves by sliding across a surface, the irregularities (tiny bumps) on both surfaces interact with each other and resist the motion. This resisting force is called sliding friction.
Sliding friction always acts in the direction opposite to the motion of the object. Its magnitude depends on the nature of the surfaces in contact and the force pressing them together. Rough surfaces produce more sliding friction, while smooth surfaces produce less sliding friction.
For example, when a book is pushed across a table, it initially moves but gradually slows down and stops due to sliding friction between the book and the table. Sliding friction is useful in daily life because it allows us to control motion, but it also causes energy loss in the form of heat.
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