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.
When an object slides over a rough surface, there is resistance to the motion of the object. The resistance is called kinetic friction. Kinetic friction is a force that the surface exerts on the sliding object. This force is parallel to the surface and directed opposite the direction of motion of the object. In addition to this, the surface exerts a force on the object that is directed perpendicular (normal) to the surface.