Why is kinetic friction always lower than maximum static friction?

[Peter G.]

I was reading about those in my textbook and they drew an example of a block resting on a ramp. The diagram showed the force of friction.

How is there friction if the block is not moving?

Thanks,
Peter G.

 

[Filip Larsen]

Look for an explanation of static friction in your textbook, or see http://en.wikipedia.org/wiki/Friction#Static_friction

 

[Peter G.]

Ok, thanks!

 

[Femme_physics]

Well, if any force is applied on the object (even if it's gravity pulling it down a slope) then there's static friction to prevent movement, or attempt to prevent it anyway (so it'll be opposite to where the force wants to cause movement). Once the force is strong enough to achieve movement on the object, static friction becomes kinetic friction, which-- curiously and interestingly enough, is always lower than the max static friction.