Fluids and Motion Pressure – Refers to a force pushing on a surface. Area is the measure of a surface. Calculating Pressure – Pressure (Pa) = Force (N) Area (m2) Pressure is equal to the force exerted on a surface divided by the total area over which the force is exerted. Pascal – The SI unit for pressure 1 Pascal (Pa) = 1 N m2

Fluids and Motion 5. Fluids – A substance that can easily flow. Fluids are able to change shape. Liquids and gases are fluids. 6. Fluid Pressure – All the forces exerted by the individual particles (atoms, molecules) in a fluid add together to make up the pressure exerted by the fluid. 7. Fluid Pressure All Around – Air exerts pressure because it has mass. 1 cubic meter of air has a mass of 1 kg. Gravity pulls on this mass & gives air a pressure.

Fluids and Motion 8. Balanced Pressure – Average air pressure at sea level is 10.13 N/cm2. Why aren’t you crushed by this pressure? 9. Pressure & Elevation – Air pressure decreases as elevation increases. At higher elevations there is less air for gravity to pull on, therefore the weight of the air is less. As the air pressure decreases your ears pop. Why?

Fluids and Motion 10. Pressure & Depth – Water pressure increases as the depth of the water increases. Water pressure is due to the weight of the water above a particular point. Also air in the atmosphere pushes down on top of the water. Therefore when one is under water, the total pressure you are under is equal to the weight of the water plus the weight of the air above you. In the deepest parts of the ocean the pressure is 100x the air pressure you experience daily.

Motion & Pressure in Fluids 11. Pascal’s Principle – When a force is applied to a confined standing fluid, an increase in pressure is transmitted equally to all parts of the fluid.

Motion & Pressure in Fluids 12. Force Pumps – Increased pressure at one end of a fluid in a container with a hole at the other end. Because the fluid is not confined by the container the fluid is pushed out of the opening. Ex. The Human Heart – Two force pumps -> One pumps blood to the lungs to pick up oxygen. The oxygenated blood returns to the heart and is sent to the rest of your body by the second pump

Motion & Pressure in Fluids Hydraulic Systems – Designed to take advantage of Pascal’s Principle -> A hydraulic system multiplies a force by applying the force to a small surface area. The increase in pressure is then transmitted to another part of a confined fluid which pushes on a larger surface area. Ex.’s: Disc Brakes of a Car Sea – Starfish Movements

Motion & Pressure in Fluids 14. Hydraulic Systems

Floating and Sinking 15. Buoyancy – Water exerts a buoyant force which acts in an upward direction against the force of gravity. So an object will feel lighter in water than in air.

Floating and Sinking 16. Archimedes Principle – states that the buoyant force on an object is equal to the weight of the fluid displaced by the object. 17. Density – Mass/Volume -> An object that is more dense than the fluid in which is immersed sinks. An object that is less dense than the fluid in which it is immersed floats to the surface.

Floating and Sinking 18. Buoyancy and Density – an object with a lighter density floats easily and is said to be more buoyant. 19. Buoyancy - A larger object will displace more fluid. This increases the buoyant force on the object. Ex. A large ship displaces a lot of water – also the ship is filled with air which is less dense than water.

Flight 20. Bernoulli’s Principle – States that the pressure exerted by a moving stream of fluid is less than the pressure of the surrounding fluid. Ex.’s would be airplane wings or a bird’s wings – The top of the wing is curved, this forces the air to travel faster over the top of the wing. Thus the air pressure is less above the wing (Bernoulli’s Principle). The higher air pressure from the slower moving air beneath the wing forces the wing upward.

Flight 21. Objects in Flight – Bernoulli’s Principle

Flight 21. Spoilers on Race Cars – Upside down wings Bernoulli’s Principle -> The higher air pressure of the slower moving air above the wing pushes the car down onto the track. The exact opposite of what occurs with an airplane’s wings.