The common uses of the wheel are obvious. Rather than travel on foot or on horse, we have learned to travel by horse-drawn carriages, cars, trains and now airplanes and rockets. The Industrial Revolution could never have occured without the wheel. Not only do industrial machines, such as we find in factories, or home appliances such as washing machines and air conditioners, depend on the wheel, even the printing press that brought learning to the masses depended on gears - toothed wheels! - to work. In other words, though the printing press was important, it simply couldn't exist without the wheel.