We started this module by discussing large, ancient buildings and wondering how their structure had mostly remained the same for hundreds of years. It is clear now that Friction plays a big role here. Due to static friction, the rocks that are on top of other rocks don't move even if there are forces acting on them.

One other thing: notice that the maximum frictional force is given by $$F_f = \mu N$$. Here, $$N$$, the normal force, depends on the mass of the object. So, the heavier the rock, the more the frictional force is. The more the frictional force is, the more stable the structure will be.

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