Have you ever stayed in a big hotel while on vacation? After checking in, you might have heard someone mention that you're in room 623 or 954 or 1475. Oh no! Do you have to carry all your heavy bags up 6, 9, or even 14 flights of stairs?

Don't worry…the hotel surely featured a mechanical device that made getting to your room a breeze. What are we talking about? An elevator, of course!

Aside from playing in the hotel pool, the one thing many kids remember about staying in a hotel is riding the elevator. Some hotels have fancy elevators with glass walls that allow you to see the hotel's courtyard while you're traveling up to your room. And who doesn't like to push those buttons and watch them light up?

But exactly how do these elevators work? Is there a team of strong monkeys behind the scenes pulling on ropes to raise and lower the cars? Not quite! It's not too far off the mark, though. Just replace the image of monkeys with a powerful motor. The elevators we ride in today are modern, technological marvels. The concept behind the elevator has been around for thousands of years, though. Ancient humans who constructed buildings saw the need for a way to move people and objects from one level to another. For example, ancient Roman architect Vitruvius wrote about Archimedes building an elevator-like device as early as 236 B.C. For a couple thousand years, all sorts of devices to raise and lower people and objects were created for particular situations. Many of these early elevators could be quite dangerous. In fact, elevator accidents could be deadly. It wasn't until 1861 that Elisha Graves Otis invented the safety elevator, which is considered by most to be the precursor to the modern elevators we enjoy today. Otis' elevator featured safety systems that would prevent an elevator car from plummeting to the ground if a cable broke. As sophisticated as they are, today's modern elevators work just like a pulley, which is one of the six simple machines you may have learned about in science class. The elevator car that you ride in has a strong metal cable attached to the top of it. That cable runs up the elevator shaft and over a sheave, which is like a pulley wheel with grooves, that holds the cable securely. A powerful motor attached to the sheave can turn the wheel in either direction to either raise or lower the elevator car. To reduce the amount of energy needed to move the elevator car, the other end of the strong metal cable is attached to a piece of metal called the counterweight. The counterweight weighs about as much as the elevator car itself plus about 40-50% of the total weight it can carry. The counterweight provides balance and makes it easier for the motor to raise an elevator car full of passengers. It also reduces the amount of braking necessary when the elevator car descends. The elevator buttons you push tell the elevator's computer system where passengers need to be picked up and where they need to go. Sophisticated computer algorithms are used to make the elevator system work efficiently. Elevator systems can even be programmed to provide more cars to certain levels during peak demand times based upon usage history.