does friction depends on area under contact force??????EXPLAIN WITH FBD N LOGICAL REASON

Friction force has NO "surface area" component. This is hard to understand (and it sounds like the teacher who asked this question doesn't quite understand either...).

Imagine this-- A block of wood with a flat bottom and a legged wooded stool sit on a smooth inclined plane. Do we have to know the contact area (surface area) of the block or the stool legs to determine the angle at which each will slide? No. We merely need to know the applied weight and the coefficient of friction between the materials.

So why does a dragster have such big smooth tires? Wouldn't thin knobby bicycle tires do as well? As far as the friction force is concerned, Yes. But the issue the dragster faces is how to transfer the engine power to the asphalt to accelerate the car. This involves HUGE problems of material strength, power, heat and wear that takes the problem far outside the narrow concerns of friction force.

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