How do scientists design roller coasters without using an engine?

Before a rollercoaster ride begins, an electric winch winds the cars to the top of the first hill. That can take a while, because some rollercoasters start off nearly 100m (330ft) in the air!

The winch has to use energy to pull the rollercoasters up the hill, but that energy doesn't simply disappear. The rollercoaster cars store it just by being up in the air—and the higher up they are, the more energy they store. They'll use the same energy to race back down the hill when the ride begins. Because they have the ability (or potential) to use in the future energy that was stored in the past, we call the energy they're storing potential energy.

Explanation:

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water pollution kills aquatic life. aquatic life includes algae and other plant life that use photosynthesis. photosynthesis takes   c02 out of the air.  

c02is a greenhouse gas.

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