1. fluids

2. 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

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 F
P A
Pssst: This works the same as the Density Triangle

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

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

12. P=F A = 1000Newtons = 1000Newtons
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)
The pressure because the area was smaller *
= 1000Newtons
100 m2
= 10N/m2
= 1000Newtons
50 m2
= 20N/m2

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

14. P=F A Double the force = double the pressure = 1000Newtons
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)
Double the force = double the pressure
= 1000Newtons
100 m2
= 10N/m2
= 2000Newtons
100 m2
= 20N/m2

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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)

21. 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

22. 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