P RESSURE, H YDRAULICS AND P NEUMATICS Discovering Science 8 Section 9.2

W HAT IS P RESSURE ? Pressure is the force acting on a certain area of surface. There are two general conclusions that can be made about the relationship between force, area, and pressure: 1.The larger the force, the greater the pressure. 2. The smaller the area, the greater the pressure.

C ALCULATING P RESSURE Pressure can be calculated by measuring the force that is being exerted and dividing it by the area over which the force is being exerted. Pressure (P) = Force (F) Area (A)

Force is measured in newtons (N) and area is often measured in square metres (m ). Therefore, the unit for pressure is N/ m. This unit is also called a pascal (Pa). A kilopascal is equal to 1000 Pa.

C OMPRESSIBILITY OF S OLIDS L IQUIDS AND G ASES Gases have large spaces between the particles. When pressure is applied to a gas, the particles can be squeezed together. This property is called compressibility. Even when a gas is compressed, there is still space between the particles.

In liquids and solids, there is very little space between the particles so when a force is applied to them, the particles cannot be squeezed together into a smaller volume. This means that liquids and solids are incompressible.

P ASCAL ’ S L AW Pascal’s Law states that the pressure applied to a confined fluid is transmitted with equal force throughout the entire container.

When a confined fluid is squeezed, this creates static pressure. The fluid does not move,but it is still capable of carrying a force. Pascal’s Law is the principle behind hydraulic systems.

H YDRAULICS Hydraulics is the study of pressure in liquids. A hydraulic system is a system that uses applied force transmitted through a liquid to move something else. Some common examples of hydraulic systems are a dentist’s chair, Jaws of Life, dump trucks, and many other types of machines.

Hydraulic systems can greatly multiply the force exerted by a liquid. Hydraulic multiplication means that liquid increases and transmits a force from one point to another. A small pressure exerted on one side of a system can be transferred to a larger area on the other side of the system. H YDRAULIC M ULTIPLICATION

P NEUMATIC S YSTEMS The study of pressure in gasses is called pneumatics. In a pneumatic system, a gas transmits a force exerted on the gas in an enclosed space. Because gasses can be compressed, pneumatic systems use compressors to build up air pressure and then when the pressure is released the particles move apart suddenly creating a force that can perform powerful tasks. Some examples of pneumatic systems are jackhammers, dentist’s drills, braking systems in busses ( air brakes).

B ODY H YDRAULICS The human body is home to one of the most efficient hydraulic systems known. The circulatory system pumps blood which is under pressure. The constant beat of the heart keeps blood moving throughout the body’s arteries, veins and capillaries. The heart creates enough pressure to squirt blood over 9 metres away. It also circulates the blood in your body three times every minute.