Take a look around you. How many machines are you aware of? Maybe you can hear a dishwasher whirring in the kitchen. Or a vacuum cleaner being run over a carpet. Possibly you can look out a window and see cars and buses passing by.
All of these are machines—tools that help us make more efficient use of our energy. With them, we can do more work with less labor. The earliest machines were quite simple, but very important. So important, that people still use them today. When you use nail clippers, scissors, or a bottle opener, you’re using a simple tool called a lever.
In the last 100 years or so, machines have become more and more complex. Electric motors that lift elevators and operate food processors, for example, operate not through the physical movement of gears, levers, and cogwheels, but by the flow of electrical currents.
