Another one, sorry! =P This stuff is really confusing..

Why doesn't friction depend on surface area?

No problem at all! Understanding friction can indeed be confusing, but it's great that you're asking questions to learn more.

Friction is the force that opposes the motion or attempted motion of two objects in contact with each other. The surface area of the objects doesn't directly affect the force of friction.

To understand why friction doesn't depend on surface area, we need to consider the two types of friction: static friction and kinetic friction.

Static friction is the force that prevents an object from moving when an external force is applied to it. It acts in the opposite direction of the applied force, and its maximum value depends on the materials in contact and the force applied. The size of the contact area affects the pressure between the surfaces, but it doesn't change the maximum static friction. Regardless of how large or small the contact area is, the force required to overcome static friction remains the same.

Kinetic friction, on the other hand, is the force that opposes the motion of an object sliding over a surface. It's generally lower than static friction. The force of kinetic friction also doesn't depend on the surface area. Instead, it depends on the normal force (the force exerted by a surface to support the weight of an object) and the coefficient of kinetic friction, which represents the roughness of the surfaces.

To determine the force of friction in a specific scenario, you need to know the type of friction (static or kinetic), the normal force, and the coefficient of friction. The surface area doesn't play a direct role in calculating friction.

I hope this explanation clarifies why friction doesn't depend on surface area! If you have any further questions, feel free to ask.