Hydraulic systems use pressurised liquid to transmit and magnify forces. You may have seen hydraulic actuators on construction equipment or other heavy machinery in the form of large "rams" -- cylinders that extend and contract to manipulate the shovels or blades of the machine. A simple model of a hydraulic actuator can be constructed with easily available materials and used to demonstrate the principles of such systems. This model may be used in support of a science fair or class project along with a poster or paper explaining how it operates, or simply as a fun activity to stimulate understanding of a common technology.
Remove the needles from the syringes. The needles will not be needed for the construction of the model.
Fill the syringes half full with vegetable oil. Do this by dipping the nozzle of the syringe into a bowl of vegetable oil and slowly pulling the plunger until the barrel of the syringe is approximately half full. Make sure that there are no bubbles in the barrel of the syringe, as this can affect the operation of the model.
Wipe away any excess oil with a paper towel and push the plungers down just far enough so that there is no air in the nozzle of the syringes.
Insert the nozzle of the larger syringe into one end of the rubber tubing. Push down on the large syringe's plunger until oil nearly reaches the end of the tubing, leaving just a centimetre or so of tubing empty so that you have something to hold on to. Now attach the free end of the tubing to the nozzle of the smaller syringe in the same way.
Operate the completed model by pushing down on one or the other plunger. The other plunger will rise. When you push down the plunger of the smaller syringe, the plunger of the larger one will rise a smaller distance but with greater force. Because its barrel has a larger diameter and therefore a larger volume, the (incompressible) fluid moves its plunger through a smaller distance. But because it moves over a smaller distance it generates a larger force. This is a "mechanical advantage," similar to how pulling the rope of a pulley with small force for a large distance can lift a large weight a small distance.
The syringes can be purchased at most pharmacies, while the rubber tubing is available at aquarium shops. If bubbles form when you are filling the syringes, push the oil out of the syringe and redo the filling process. If you have difficulty getting the end of the tubing to fit over the syringe nozzles, submerge the ends of the tubing in hot water for a few minutes. This will expand the rubber tubing and also make it softer and more malleable. Don't push down on the plungers when inserting the nozzles of the syringes into the tubing or oil may be pushed out of the syringes, creating quite a mess.
Be careful not to prick yourself with the discarded needles; they are extremely sharp.
Things you need
- 20ml syringe
- 100ml syringe
- Rubber tubing (10-15 cm)
- Vegetable oil