: a substance that has the capacity to flow and assume the form of the container it has been placed in. Fluid: a substance that has the capacity to flow and assume the form of the container it has been placed in. Ch. 3: What is a Fluid? Particle Model Liquid: particles close together, weak forces of attraction; slide passed each; take shape of container. Gas: particles far apart, no forces of attraction. Gases move in every direction; take up all available space. Are 100% adaptable All liquids and many gases are fluids. Ex: water, milk, blood, saliva, air, helium, ozone. Arrangement of particles makes a substance a fluid. 2 types: compressible fluids and incompressible fluids.

Compressible Fluids Is a fluid whose volume can change in response to change in pressure. Ex: gas is compressible Incompressible Fluids Is a fluid whose volume cannot be varied. Ex: liquids What is pressure? Pressure is the result of a force applied in a perpendicular fashion to a surface. Involves both force and surface area. What is a force? Force is an action that modifies the movement of an object (accelerate, slow down, stop) or causes the shape of an object to change or attraction. What is surface area? Surface dimension of object. To measure the pressure being exerted, we need to know the area of that surface.

Force and Pressure The stronger the force the greater the pressure. If force increases, pressure increases. If force decreases, pressure decreases. Surface Area & Pressure The greater the surface area exposed to a force, the less pressure. If the surface area exposed to a force increases, the pressure decreases. If the surface area exposed to a force decreases, the pressure increases. Calculating Pressure P = F A P is pressure, measured in Pascals (Pa) F is force, measured in Newtons (N) A is the exposed surface area, measured in m 2

Pressure Exerted by Fluids Particles in a fluid are in constant motion, pressure is exerted equally in all directions. Incompressible fluid –Force exerted comes from the mass of the fluid situated above the object. –The more fluid above the object, the greater the force and pressure by the fluid. –The denser the fluid the greater the pressure. –Instruments to measure: depth gauge, U-shaped manometer, tonometer. Compressible fluid: –Pressure depends upon: # of collisions with fluid particles; the more collisions the greater the pressure. Instruments to measure: u-shaped manometer, pressure gauge

Pressure Exerted by Compressible Fluids Factors affecting # of collisions: 1.# of particles; the more particles the more they collide 2.Temperature: increase temp., increases particle speed, increases # of collisions. 3.Volume of fluid: is variable; o at the same temperature and particle # (vice versa): if volume increases, pressure decreases (less collisions). If volume decreases, pressure increases (more collisions). *Pressure of a compressible fluid is inversely proportional to its volume. Atmospheric pressure : the pressure exerted by the air that makes up our atmosphere. It changes at different altitudes. At sea level it is kPa o Instrument to measure is a barometer.

Principles of Variations in the Pressure of Fluids 1 st principle: fluids move from an area of high pressure towards an area of low pressure. Ex: gas canister, exhalation and inhalation 2 nd principle/Pascal’s principle: pressure applied to the surface of a fluid inside a closed container gets uniformly distributed to every part of the fluid. Ex: pushing the plunger of a closed syringe, brakes (brake fluid) in a car, heart pumping blood 16 kPa (120 mm Hg) to 10 kPa (75 mm Hg). 3 rd principle: A transfer of pressure in a fluid can increase the force involved. Ex: hydraulic system