How Disney's Drop Rides Work
Two of the most jaw-dropping Disney attractions - the Tower of Terror and Guardians of the Galaxy: Mission Breakout! - employ some plussed up elevators for an exciting and sometimes nauseating ride experience. Dropping 13 stories at a speed faster than freefall requires some pretty interesting science!
The Ride Vehicle
Most of the sources I consulted say that the Guardians of the Galaxy gantry lift or Tower of Terror elevator is an example of a simple traction elevator. Traction elevators operate as pulley systems. For Disney's versions, each elevator shaft has two "drums" or wheels with cables running over them attached to motors located on the top floor. The cables from one drum are attached to the elevator vehicle or "cab"; the cables from the other drum are attached to a counterweight. Another set of cables is attached to to the bottom of the cab, goes around another pulley wheel at the bottom of the shaft and is attached to the bottom of the elevator cab.
This design is pretty clever because it relies on a few laws of physics to reduce the amount of electricity required to run it! If we want to move the elevator up, we have to do work (a formal concept in physics, not like the chores that Cinderella did every day) in order to increase its potential energy. The physics concept of work is the amount of force applied across some distance: if we want to move the elevator up 13 stories (or about 130 feet) we have to put in a lot more work than if we wanted to move it 13 inches. The force that is applied across that 13 stories or 13 inches would have to be equal and opposite to the weight of the cab full of people.
The counterweight helps reduce the amount of force and thus the amount of work that the motors have to generate because gravity pulling down on the counterweight does some of the work for the motor. Gravity pulling down on the counterweight causes a force on the cables that is in the same direction as the elevator cab going up. But usually this counterweight doesn't have as much mass and therefore not as much weight as the elevator, so the motor has to do the last bit of work to pull up on the cables attached to the cab.
For the cab to be "dropped" down the shaft, gravity could do all the work, but that wasn't enough for Disney Imagineers. For the fall, an engine generates up to 1200 volts of electricity (10 times the electricity in a standard American outlet) to spin the motor in the opposite direction and pull down on the elevator. Combining this additional pull from the motor-driven cables accelerates the cab at a rate faster than gravity which makes for a shriek-worthy sensation.
The Experience
In real life, many people are scared of the possibility of an elevator plummeting to the ground, no matter whether it's 13 stories or just 3. But it is much more likely you'd wind up stuck in an elevator (sorry for the claustrophobes out there!) than it is to have an elevator crash all the way to the ground because elevators are equipped with so many back-up systems to prevent them from falling. Elevators only need one functioning cable to operate normally but they usually have at least three (each Disney ride elevator has five). Even if all of the cables were to be non-functional, which is highly unlikely due to regular maintenance checks on the wear and tear of the cables, each elevator has two braking systems which are also examined routinely. One braking system works to stop the motor from spinning and the other stops the elevator from falling by extending a brake into the guide rails of the shaft.
Even going into the ride knowing that the ride is totally safe, the feeling of freefall can be quite frightening. Freefall is the name for when the only force acting on an object (for example, 21 human bodies in a metal box) is the acceleration due to gravity (32.2 feet per second per second) but we know from our exploration above, that the elevator falls even faster than freefall due to the motor putting in work. The elevators on Guardians of the Galaxy and Tower of Terror reach speeds of 39 miles per hour!
I have to save the science behind the magic of the Fifth Dimension portion of Tower of Terror at Disney's Hollywood Studios for another day, but comment below with which version of this terrifying tower ride is your favorite!
Citations
Translation of a German Film about Paris's Tower Construction
More on Tower of Terror Motors
How Counterweight Works Mathematically
More Fun