Lots of the rides at the fair used hydraulics, either to make the ride go up and down, or, in the case of this one, lift it into place and hold it securely while it operates. Hydraulics is the use of a liquid, usually oil, to do work by applying a force. Although air pressure can be used to do the same thing, air won't work for supplying large forces because air will compress, but a liquid won't. Here is a close-up of the molecules in a gas. They are far apart, which means if you use them to supply a force, they will just compress ... move closer together. Pushing heavy loads with a gas would be like trying to push with a marshmallow ... it would just squish together. Here is a close-up of a liquid's molecules. The molecules are already as close together as they can get, under normal circumstances. Pushing with a liquid is just like pushing with a steel rod, as long as you keep the molecules confined (since a liquid has no fixed shape). The advantage of pushing with a liquid in a hydraulic system, instead of steel rods, is that a liquid can bend around corners; it can follow the shape of the hose that holds it. You can supply a push to the liquid in an original direction, and that push will bend itself around corners and go to where you need the force applied. Here's a diagram of a simple hydraulic system like the one holding up the ride above. Oil is kept in a tank somewhere out of the way, and a pump sends it through the hose under pressure. This force transmits itself through the hose to the end, where it can push against something. In this case, it pushes against the inside of a set of steel tubes which slide one inside the other. The oil pressure pushes these tubes outwards so they extend in length. This is called a hydraulic ram, and it's the same as the one used in your car's jack, or at the service station where you get your car fixed. Street Fair Physics