We just learned about Hydraulics, using water to move things.
Another part of hydraulics is a Hydraulic Cylinder.
This is a tube that is filled with liquid like oil, and a special motor pushes more oil into the cylinder which pushes something like a big metal rod out of the tube.
![hydraulic cylinder](https://upload.wikimedia.org/wikipedia/en/4/47/Cutawayweldedcylinder544x123.jpg)
(from: wikipedia - hydraulic cylinder)
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