I had always assumed that coffeemakers had some sort of a heating element and a small water pump to force the water through the coffee grounds.
I was sadly mistaken.
Being a college student with far too much time on my hands, I decided to take my trusty $9 Wal-Mart cofeemaker apart to find out for sure.
It turns out that when you pour the water into the water compartment, it goes to the bottom of the machine, directly beneath the hot plate part. As you might expect, on the underside of the hot plate is a heating element. What surprised me is that on the other side of this heating element (just beneath it) is an aluminum tube connected directly to the water compartment on one end and running to the top of the machine on the other.
When you flip the switch on, the heating element gets hot, and the water flows into the aluminum tube with the help of gravity. When the water gets hot enough, it boils up through the tube towards the top of the machine. When it gets there, it just drips down through the coffee grounds and into the pot where it is kept warm until the coffee is served.
Pretty cool, huh? Water gets pumped through the machine, all without a single moving part! Except, of course, for the valve that prevents the boiling water from flowing back into the cold water compartment.