**Top Thrill Dragster**

There are sets of proximity sensors on the top of *Dragster*'s hill that measure the time interval as the train
passes two locations. By knowing the time difference and the distance between sensors, the ride's computer can calculate the train's speed
as it passes over the top of the ride. The computer averages the speed of the last three trains when it calculates
the forces required for the next launch. So, if there are three train-loads of lightweight passengers followed by a
train full of heavy passengers, there is a chance that the fourth shot will result in a "rollback" due to an
underspeed launch. Because 18 170-pound passengers add over 3,000 pounds to the weight of a train,
adding the weight of these water bottles during testing helps ensure that the computers adequately measure the
amount of effort required to launch a fully loaded train.

©2018 by Joel A. Rogers.