8th Science NCERT Chapter 9

A vehicle slows down when brakes are applied because the force of friction between the brake pads and the wheels opposes the motion of the vehicle, leading to a decrease in speed until it stops.

The force of friction is the force that opposes the motion of an object when it moves over the surface of another object. For example, when pushing a book on a table, the force of friction between the book and the table slows down the book's motion until it stops.

Surface irregularities on two surfaces in contact cause interlocking between them, requiring a force to overcome this interlocking and move the surfaces. The more irregularities present, the greater the force of friction, making it harder to move objects over rough surfaces.

Friction is considered a necessary evil because it is essential for various everyday tasks like holding objects, walking, writing, driving, fixing objects, and generating heat. Without friction, tasks such as holding a glass, walking, driving, writing, or construction would be impossible.

Static friction is the force required to overcome friction at the instant an object starts moving from rest, while sliding friction is the force needed to keep the object moving at a constant speed once it is in motion. Static friction is slightly higher than sliding friction as it includes the initial force to break the static state of an object.