Chapter 3 Behaviour of Fluids Text Book: pp. 65 to 84 Related Concepts: particles, pressure,

Fluids A fluid is a substance that can flow, and can take the shape of its container. Liquids are fluids. So are gases! Particles (that is the molecules) of fluids are held together by weak forces, so they can move easily

Two types of fluids Compressible fluids (gases) The volume of a compressible fluid can be reduced because particles are far apart. Incompressible fluids (liquids) The volume cannot be reduced. It is impossible to squeeze a liquid into a smaller space because particles are very close. Plugged syringe Gas in syringe Liquid in syringe

Pressure Pressure is a force applied to a surface Fluids can exert a force on the inside of their containers This force is a form of pressure. The formula for pressure is: Where: P=pressure in Pascals (Pa) F= force in newtons (N) A= area of the surface (m2)

At The Molecular Level: Pressure in fluids is caused by particles (molecules) colliding (or bumping) against the sides of the container. The harder and faster the molecules collide, the greater the pressure inside the container! P increases with more particles, higher temperature and decreased volume of container.

Effects of Water Pressure If you swim deep under water, you will feel a force inside your ears. The deeper you go, the stronger this force feels. If you swim too deep, your ears will begin to hurt. The pressure comes from the weight of all the water above you pressing on all your surfaces (like your eardrums) Your ears hurt because of water pressure pushing in on your eardrum.

Atmospheric Pressure The air in the atmosphere also has weight. Atmospheric pressure is caused by the weight of the air pressing on us. Air is not very heavy, but the 100km of atmosphere above us adds up to a pressure of over 100 kilopascals That’s equivalent to one kilogram for every square centimetre. Or nearly 15 pounds per square inch This is a barometer. The mercury in the tube is being held up by air pressure.

Effect of Air Pressure If you fly in an airplane, at a high altitude, sometimes your ears will hurt. This is the result of low air pressure around you. The higher air pressure in your lungs puts force on your eardrum pushing out.

Pressure and Your Eardrum High pressure outside Pressure Inside

Read Textbook pages Workbook pages 37-39 to 40-42

Mechanisms Related to Variations in Fluid Pressures First Principle: A fluid will flow from an area of high pressure to an area of low pressure. Low Pressure Pressure High

A leak releases pressure from the whole system Second Principle: Pressure applied to the surface of a fluid inside a closed container is distributed to every part of the fluid. Called “Pascal’s Principle” It means that pressure is evenly distributed inside a closed container or hydraulic system. A puncture or weak spot will release pressure from the whole container or system. A leak releases pressure from the whole system Pressure is Distributed

Third Principle: A transfer of pressure in a fluid can be used to increase the force involved. This is called the “hydraulic principle” It is used to make car lifts and other heavy equipment work. It can also be used in hydraulic brakes, where pushing the brake pedal puts pressure on a fluid, which then puts pressure on the brake calipers.

How Hydraulics Works Small Force Fluid Narrow cylinder Large Force piston Fluid Narrow cylinder Large Force Piston Wide cylinder

Other uses of hydraulics cylinders Lifting heavy weights Shock absorbers Making cars bounce Hydraulic cylinders Hydraulic cylinders hidden over front wheels, hydraulic pump in trunk.

Natural Uses of Pressure and Hydraulics.

Your Heart acts like a Hydraulic Pump! Blood from the body collects in the vena cava and right atrium. Blood moves into right ventricle Right ventricle closes, pushing blood towards lungs Blood from lungs collects in left atrium Blood moves through valve into left ventricle Ventricle closes, pushing blood towards the body, and creating blood pressure. Left Atrium Right Atrium valve valve Left Ventricle Right Ventricle

Your Lungs Use Pressure to Work When you inhale, you create low pressure in your lungs. This draws air into your body by increasing the volume of your lungs. When you exhale, you create high pressure in your lungs, forcing air out of your body by increasing the volume of your lungs.

Wind is Caused by Pressure. Air (a fluid) moves from areas of high pressure to areas of low pressure The flow of air causes wind. Wind Wind

Workbook pages 43 to 48