# fluids

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## fluids

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1. fluids

2. Fluids • Afluidis 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

3. 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 *

4. 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 *

5. Pressure • 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

6. Pressure • When we apply a force on a fluid, the fluid exerts a force on whatever contains it *

7. F P A • Pressure (newtons/meter2) = Force (newtons) Area (square meters) • The international unit for pressure is the PASCAL (Pa) • 1Pa = 1N/m2 this is a relatively small unit • kPa (1000Pa) is used to measure atmospheric pressure

8. Other units are used to measure pressure: • Millimetres of mercury (mmHg) • Atmosphere –normal atmospheric pressure at sea level • 101.3kPa=760mmHg=1atm *

9. 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)

10. If the person stands on a nail the foot will be punctured How ever if the person lay down on a bed of nails the skin would not be broken Why? What is the similarity with snowshoes? *

11. By changing the area the force is acting on you notice an increase in pressure Increase area decrease pressure Decrease area increase pressure *

12. Pressure varies inversely proportional to the surface area or force applied 5N/m2 0.5m2

13. If 1,000N were applied to an area of 100m2 what would the exerted force be? P=F A • If the same force (1000N) were applied to ½ the previous area( 50m2) P=F A • The pressure because the area was smaller * =1000Newtons 100 m2 = 10N/m2 =1000Newtons 50 m2 = 20N/m2

14. Did You Know? • There is more pressure exerted under the heel of a stiletto shoe than under the Empire State Building?

15. The relationship between pressure and the force applied • The weight of water exerts a force upon anything submersed in it • The pressure at the bottom of the barrel = the weight of the column of water directly above an area of one square cm • If the barrel were 1m high there would be 1000cm3 of water (1kg) pushing down (1cm3 =1g) * 1kg One cm2

16. When a person dives underwater the water column above the person pushes down on them • The deeper you dive the more pressure is exerted on your tissues • You can feel the pressure on the ear drums ( painful) - more depth and you can rupture them *

17. pressure is directly proportional to the force applied Pressure (N/m3) Force (N)

18. Look at these examples again: • If 1,000N were applied to an area of 100m2 what would the exerted force be? P=F A • If increasing the force (2000N) were applied to the same area( 100m2) P=F A Double the force = double the pressure =1000Newtons 100 m2 =10N/m2 =2000Newtons 100 m2 =20N/m2

19. 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

20. 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

21. 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

22. 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

23. The Bottle Diver Activity • Rinse out a 2 L pop bottle and then fill it to the top. • Break off the top of a wooden match and put it in the bottle. • Cap the bottle tightly. • Compress the bottle and see what happens to the match head. • Repeat

24. The Bottle Diver Activity • Why does the Bottle Diver dive? • Can you make the divers suspend in one place in the bottle? • What is happening at this point? • If you pour out half of the water in the bottle, it becomes much harder to sink the diver.  Why?

25. The relationship between volume and pressureof 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

26. 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)