The blame has been pinned, squarely and often, on inadequate oversight of U.S. financial institutions, which created ever more complex and risky mortgage instruments, lured people to buy homes they could not afford, and brought the economy crashing to the ground.
Motion on the Earth does not take place in a vacuum. When one thing moves, it moves through or across another. When a wheel turns on an axle, the two surfaces rub against one another. This is called dry friction. Grease can be used to separate the solid metal parts, but this just reduces the problem to layers within the grease sliding past one another.
As a safety precaution in case the bolts that hold the wheel halves together have been damaged or weakened. The braking action of a Cleveland disk brake is accomplished by compressing a rotating brake disk between two oppostie brake linings. How is equal pressure on both sides of the rotating disk assured? By allowing the caliper to float to automatically equalize as pressure is applied to the rotor.