A Drop Tower is a popular ride in amusement parks. To make the ride as energy efficient as possible, one can set up an electric motor and regenerative battery system in which energy from the battery is used to drive the electric motor to lift the riders to the top of the ride. As the riders descend down the ride, the "falling" energy is used to recharge the battery. Given that friction is unavoidably present, explain why this ride is an example of an irreversible process.
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A process that produces no entropy is a reversible process because it can also be made to happen in the reverse direction. In this case the forward direction of the process is the ride being raised (which lowers the charge in the battery), and the reverse direction is the ride going back down (which increases the charge in the battery). The charge cannot be fully returned to the battery after the ride is completed because the friction present in the ride transforms part of the battery energy into heat energy which is lost to the environment (which produces entropy), and this cannot be recovered. Therefore the ride (on the way up or on the way down) is not a reversible process.
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