Forces - Hydraulics

This means that liquids can be used to transmit pressure over long distances and round corners by using tubes in a hydraulic system.

Even better than this, hydraulic systems can be used to magnify small forces to make them very large. They are used in a wide range of machines like car braking systems, cranes and diggers.

These systems are extremely powerful. You may have felt the power of hydraulic systems at school. A common experiment is to half fill a large syringe with water and connect it via a length of plastic tubing to a smaller syringe, also half-filled with water. One person holds the larger syringe and a second person holds the smaller one. They then have a competition to try to push the plungers to try to fill the other person's syringe. The person with the smaller syringe always wins easily (either that or the tube comes off one of the syringes because the pressure is so high!) since the force they use is magnified.

This idea is used for car braking systems. In car braking systems, the syringes are replaced by sealed metal cylinders filled with a special fluid (brake fluid). The pipes that are used to join the cylinders are very strong and fixed very firmly to the cylinders. When the brake pedal is pushed, it operates something called a servo which magnifies the force from the driver's leg. The servo is connected to the brake master cylinder which is the equivalent to the small syringe. The brake pipes connect the master cylinder to 4 separate slave cylinders. These are the equivalent of the large syringe. As the plunger of the master cylinder is pushed in, the pressure is transferred through all of the pipes to the slave cylinders. The slave cylinders have a larger cross-sectional area than the master cylinder which magnifies the pressure. This pushes the brake pads against the brake disk (or brake drum on some cars), converting the kinetic energy into heat energy and slowing or stopping the car.

Pressure is defined as the force acting per unit area. It is therefore calculated by dividing the force that is creating the pressure by the area over which it is acting. When the force is in newtons and the area in square meters, the pressure will be in pascals (Pa). The unit is named for the French mathematician, Blaise Pascal, who also carried out scientific research into hydraulics. He is said to have invented the syringe, although more primitive versions had been used by the Romans and an Iraqi/Egyptian physician. It was Pascal who discovered that liquids transmit pressure in all directions and that knowledge has become known as Pascal's law. He invented the hydraulic press, a very powerful machine that can be used to cut and shape even metals. He showed that the pressure increases with the depth of a liquid and not the weight, as was thought before his work. Pascal was amazingly talented and his name has been given to many other scientific and mathematical things such as Pascal's triangle, a computer programming language and more. He was only 39 when he died.