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# Unit 23 - Fluid Pressure

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Properties of Fluids

Properties of Fluids

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• 1.How to define the term pressure for a liquid in motion?

2.We describe pressure as Force per Area, When area of flow decreases we say velocity increases and pressure decreases but Isn''t pressure should raise due to reduction in area of conduit as per the basic definition? Plz answer above Questions?Thank you.

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### Transcript

• 1. Forces in Fluids
Chapter 23
• 2. Thought Questions
Why is the electricity produced at the bottom of dams?
When you catch a deep-sea fish, why does its eyes pop-out?
Why do your ears pop on an airplane or up in the mountains?
• 3. Pressure

Pressure is equal to the force applied to a surface, divided by the area.
• 4. Equations for Pressure
Pressure = Force/surface area
• Pressure = Newtons (Kg x m/s2)
side x side
• Units are in Pascals or N/m²
• Fluids
A substance that can easily change its shape, such as liquids and gases.
• The molecules in a fluid have a certain amount of force (mass and acceleration) and exert pressure on surfaces they touch.
• 5. FLUID PRESSURE
• All the molecules add up together to make up the force exerted by the fluid.
• High
Microburst - High Pressure Air
High Pressure
• 6. Low Pressure
L
Rising Air
Suction
L
• 7.
• Air has a mass of 1Kg/m³
AIR PRESSURE
• Gravity creates an air pressure of 10.13N/m³ at sea level.
• Pressure and Elevation
• Air Pressure decreases as elevation increases.
Climbers above 20,000 feet need oxygen because the air is so thin
• 8. Pressure and Elevation
• Air Pressure decreases as elevation increases.
• 9. Astronomical telescopes are placed on mountain tops because the thinner air means less interference with the stars
Mauna Kea at 13,700 feet
Is above 40% of the atmosphere
• 10. Extreme Elevations
Commercial flights fly higher than you can breathe. So, they must pressurize the cabin
Mount Everest at 29,600 feet
Is above 70% of the atmosphere
35,000 feet
• 11. Extreme Elevations
Astronauts have no actually left the atmosphere. The microscopically thin atmosphere results in drag on spacecraft and satellites.
Nonetheless, it is far too thin to breathe and cold to survive without spacesuits
100 km
• 12. Highest Pressure
Very Low pressure
Higher Pressure
The whole system is a low pressure, but it is extremely low in the eye.
• 13. Highest Pressure
Very Low pressure
Higher Pressure
Pressure always flows from high to low, which creates the high velocity winds toward the eye.
• 14. Storm Surge
Very Low pressure
Higher Pressure
The Low Pressure creates a vacuum that pulls water up into a dome. The high winds push this dome on shore.
• 15. Storm surges are the leading cause of damage
Very Low pressure
Higher Pressure
The force of the air moving toward the eye causes extreme winds in excess of 100 mph.
• 16. Pressure and Depth
• Water pressure increases with depth.
• Water Pressure
Marianas Trench = 10,911 m (35,800 ft) or 1,100 atmospheres.
That is the equivalent of an average-sized person holding up 48 jumbo jets or 400 times the pressure in automobile tires.
• 17.
• 18. Pascal&apos;s Principle
• When a force is applied to a confined fluid, the increase in pressure is transmitted equally to all parts of the fluid.
• 19. These styroform cups were crushed outside of submarines.
• Transmitting Pressure in a Fluid
When force is applied to a confined fluid, the change in pressure is transmitted equally to all parts of the fluid.
• 20. Hydraulic Devices
In a hydraulic device, a force applied to one piston increases the fluid pressure equally throughout the fluid.
• 21. Hydraulic Devices
By changing the size of the pistons, the force can be multiplied.
• 22. Hydraulic Brakes
The hydraulic brake system of a car multiplies the force exerted on the brake pedal.
• 23. Buoyancy
The tendency or ability of an object to float.
• 24. Buoyancy
The pressure on the bottom of a submerged object is greater than the pressure on the top. The result is a net force in the upward direction.
• 25. Buoyant Force
The upward force exerted by a fluid on a submerged or floating object.
• 26. Buoyancy
The buoyant force works opposite the weight of an object.
• 27. Archimedes’ principle:
Buoyant Force on an object immersed in a liquid equals the weight of the liquid displaced.
• 28. Density and buoyancy: An object that has a greater density than the fluid it is in, will sink. If its density is less than the fluid it will float.
Density
• 29. It does not matter that Mercury is a liquid. It is so dense, most things float on it
• 30. Buoyancy of gases in liquids
Buoyancy of gases in gases
Gases have less density than water, so they rise up to the surface
Some gases, like Helium, are lighter than air and rise.
Some gases, like carbon dioxide, are heavier than air and sink.
• 31. How do super heavy container ships float?
• 32. A solid block of steel sinks in water.
A steel ship with the same mass floats on the surface.
• 33. A solid block of steel sinks in water. A steel ship with the same mass floats on the surface.
Air
steel
• 34. Take the mass of the displaced area (steel and air) and compare it to the mass of the water of that volume.
If the displaced area weighs less it will float.
Water
• 35. Density
Changes in density cause a submarine to dive, rise, or float.
• 36. Density
Changes in density cause a submarine to dive, rise, or float.
• 37. Density
Changes in density cause a submarine to dive, rise, or float.
• 38. Density
Gases can actually be made from solids using chemical reactions to create additional buoyancy.
• 39. DENSITY OF WATER
1g/cm³
or 1 g/ml