Tantalizing trills of a triangle, a cadence of carnival bells, then a countdown – 5…4…3…2…1! – and the screaming begins.
California Screamin’ at Disney’s California Adventure is set to close January 8th, 2018 and be re-themed with an Incredibles theme to become the Incredicoaster. Today, I’ll explain some science concepts integral to the launch of this awesome ride.
How does Screamin’ launch you from 0 to 55 miles per hour in under 5 seconds? Most roller coasters rely on a motor and chains to pull the train up a lift hill (the initial tallest hill) to provide enough potential energy to make it all the way around the track, but Screamin’ manages to send a train around the longest looping roller coaster track (6072 feet!) without a mechanical lift hill. Instead, this roller coaster uses a linear induction motor. How does a linear induction motor work? In a few words, with high-powered electromagnets and electromagnetic induction. To explain further, let’s review some basic physics.
Charges (like electrons) moving together in one direction, like in a wire conducting electricity (literally the movement of electrons) create an electromagnetic field around the flow of charges. When two magnets or two electricity carrying wires creating electromagnetic fields are brought close to each other, the electromagnetic fields between the two electromagnetic objects combine depending on the direction. If the fields are going in the same direction, the force created by the field is stronger between them; this occurs when magnets of the same polarity come into proximity with one another. When the two fields are going in opposite directions, a weaker force is created like when you combine a negative number (-5) and a positive number (7) to get a number that has a smaller absolute value (2) than either original number; this occurs when magnets of opposite polarity come into proximity with one another.
Like in other domains of physics and chemistry, an equilibrium, in this case of forces, is the most stable and thus desirable state. In order to get rid of the stronger or weaker forces, the magnets want to move to a state of equilibrium. When magnets of the same polarity create a stronger force between them, moving away from or repelling each other leads to an equilibrium state.
The launch system for California Screamin’ employs this idea of movement as a result of repelling magnets to move the train forward. There are several slots in the track of California Screamin’ that have electromagnets (unclear whether these are coils of wire or metal plates) with current flowing in one of three states (inward direction, outward direction, or not flowing at all) regulated by switching on and off a connected battery at different times. This battery is controlled such that each small section has an electromagnetic field going in a different direction from the section adjacent to it.
After the train is in position on the launch section of the track, the electromagnetic fields at the beginning of the launch section are turned on by “a 25-megawatt transformer [feeding] a 5,000 horsepower variable frequency drive” in a “100-yard-long room beneath the ride” according to this New York Times article. The magnetization of the track causes movement of electrons in a metal blade attached to the bottom of the train so that the electrons align with the electromagnetic field of the track. This movement within the metal blade creates electromagnetic fields within the metal blade called eddy currents. The electromagnetic fields of these eddy currents interact with the electromagnetic fields of the track to create repulsions and move the train forward. This process continues as the current in each section of track cycles through each possible state (in, out, or off). The wheels of the coaster keep it guided along the track as the train picks up speed with each subsequent repulsion and the riders shriek with delight (or fear).
The same process is at work when the coaster needs to pick up speed over the highest hill after the launch as well as any time the coaster needs to brake (although in this case, the electromagnetic fields work to push the coaster in the opposite direction, effectively slowing it down).
Can you guess which other Disney rides use this same technology?