FLUIDS Fluids A fluid is a substance that
FLUIDS
Fluids A fluid is a substance that has: no definite form Is able to flow in all directions All liquids and gases are fluids The body is full of fluids- gas and liquid
Fluids Powders such as sugar, flour or sand are not fluids even though they have no form and flow They are made of small particles of definite form *
Properties of fluids Fluid properties vary from one to another. Viscosity –the ability of a liquid to flow Honey – high viscosity Water – low viscosity Density Humans use the properties of fluids for in various systems: refrigeration, hydraulic systems, air bags, anaesthetic agent *
Pressure is the measure of the amount of force exerted on a certain area When we push on an object we apply a force on it If the force is high enough can move or even deform the object
Pressure When we apply a force on a fluid, the fluid exerts a force on whatever contains it *
Pressure (newtons/meter 2) = Force (newtons) Area (square meters) F P A Pssst: This works the same as the Density Triangle The international unit for pressure is the PASCAL (Pa) 1 Pa = 1 N/m 2 this is a relatively small unit k. Pa (1000 Pa) is used to measure atmospheric pressure
Other units are used to measure pressure: Millimetres of mercury (mm. Hg) Atmosphere –normal atmospheric pressure at sea level 101. 3 k. Pa=760 mm. Hg=1 atm *
The relationship between pressure and the area on which the force is applied The force exerted on a floor by a person standing on it consists of the person’s mass and the gravitational pull acting on it This is what we call a persons weight = (mass x gravity)
By changing the area the force is acting on you notice an increase in pressure Increase area Decrease area decrease pressure increase pressure *
Pressure varies inversely proportional to the surface area or force applied 5 N/m 2 0. 5 m 2
If 1, 000 N were applied to an area of 100 m 2 what would the exerted force be? P=F A 100 m 2 If the same force (1000 N) were applied to ½ the previous area( 50 m 2) P=F A = 1000 Newtons = 10 N/m 2 = 1000 Newtons = 20 N/m 2 50 m 2 The pressure because the area was smaller *
pressure is directly proportional to the force applied Pressure (N/m 3) Force (N)
Look at these examples again: If 1, 000 N were applied to an area of 100 m 2 what would the exerted force be? = 1000 Newtons = 10 N/m 2 P=F 100 m 2 A If increasing the force (2000 N) were applied to the same area( 100 m 2) = 2000 Newtons = 20 N/m 2 P=F 100 m 2 A Double the force = double the pressure
Particle theory to explain pressure A tire pumped up with air has a force exerted upon it by the air inside. If the pressure is high enough the tire will remain firm even if pressure is applied to it This is explained by the air molecules inside the tire having lots of energy hitting the walls Adding more “air “ increases the number of molecules pushing outward = harder tire
In the body, fluids exert pressure on blood vessels (arterial pressure) The pressure difference causes fluids to move (from high pressure to low pressure) Lungs – air moves into lung
Compressible and incompressible fluids Compressibility is the capacity to reduce the volume by exerting a force A gas is a fluid that can be compressed because its particles are farther apart Air tanks for scuba divers, propane tanks
Liquids are incompressible Hydraulic brakes Incompressible- impossible to decrease the volume by exerting a force Instead of a change in volume there is a transmission of force from one particle to another inside the substance (like dominos) The blood forced through vessels by the pumping heart
The relationship between volume and pressure of compressible fluids Gases which are compressible fluids do not have a definite volume (it fits the container) If the container is flexible (balloon) then the volume can change
The volume and pressure are interrelated At a given temp. the larger the volume the lower the pressure (molecules farther apart) Decrease the volume the higher the pressure (more molecules hitting walls)
How Fluids Move Fluids move from areas of high concentration to areas of low concentration If water is the fluid that is moving, this is called osmosis Any other substance (fluid) and the process is known as diffusion
Diffusion Substances, including fluids, can move from an area of high concentration to an area of low concentration by diffusion BUT The membrane the fluid is passing through must be permeable or semi-permeable Semi-Permeable Membrane: a membrane (layer of cells) that allows certain substances (fluids, nutrients, water, salts) to pass but blocks others
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