Mechanical advantage is a measure of the force amplification achieved by using a tool.
A compound machine is a combination of at least two simple machines. Simple machines can be a lever, a wedge, a while + axle, an incline plane, a pulley, and a screw.
There are many examples of compound machines. One of them is a showel that combines a wedge (the scoop part of shovel) and a lever (the handle to transfer the force to lift).
A much more complex compound machine is a bicycle, comprising simple machines ranging from wheels and axles, to screws, and levers (think of the pedals).
40% of the Earth's surface is covered by continental crust.
The moveable type drastically changed society. Its primary impact was the distribution of knowledge. Since people could now type books, rather than handwriting then, literary works could be shared faster than ever before. This had a massive impact on education.
