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.
9.2: Friction and Traction. One of the most important principles students must learn before they can begin drivetrain design is that of Friction. FRICTION is the force that opposes motion when two surfaces rub together. It is a reaction force only. It occurs when two surfaces are in contact and a force is applied such they slide along one another. If an object has no forces causing it to try to move, there can be no friction. No applied force, no reaction force.