Downloaded 89 times
Uploaded byAlbania Energy Association
Lecture 02 density, pressure and pascal's principle
This document provides an overview of fluids, including density, pressure, and Pascal's principle. It defines a fluid as a substance that flows and takes the shape of its container. Density is defined as mass over volume. Pressure is defined as force over area. Pascal's principle states that pressure increases with depth in a fluid and is transmitted equally in all directions. The document includes demonstrations of these principles using various devices like pistons, tubes, and hydraulic chambers.
In this document
Powered by AI
Lecture on fluids covering density, pressure, and Pascal's principle.
Fluids are substances that flow and adapt to their container's shape. Includes gases, liquids, and granular materials.
Definitions of density (ρ = m/V) and pressure (p = F/A) with units: kg/m3 for density and Pascal (Pa) for pressure.
Earth's atmospheric pressure at sea level is approximately 1 atm or 1.013 x 10^5 Pa. Demonstration on pressure's effect.
Understanding how pressure varies with fluid depth, demonstrated using an imaginary box of fluid.
At a given depth in a connected container, pressure remains constant, maintaining equilibrium across fluid levels.
Experiment exploring pressure equilibrium in a U-tube with two different liquids, determining density relationships.
Application of pressure concepts in water towers, demonstrating pressure height relationship in flat areas.
Physics example to calculate the pressure in the mouth while sucking liquid through a hose, concluding at 0.46 atm.
Description of Pascal's principle, which states pressure changes in an enclosed fluid are transmitted throughout.
Overview of hydraulic systems showing force relationships using cross-sectional areas and distances, maintaining energy.
Interactive activity about hydraulic chambers analyzing block placements and pressure difference outcomes.
Methods of measuring pressure with barometers and manometers, detailing absolute and gauge pressure principles.
More Related Content
Similar to Lecture 02 density, pressure and pascal's principle
Lecture 02 density, pressure and pascal's principle
- 1. Lecture 2 Fluids: density,pressure, Pascal’s principle.
- 2. What is afluid? Fluids are “substances that flow”…. “substances that take the shape of the container” Atoms and molecules must be free to move .. No long range correlation between positions (e.g., not a crystal). Gas or liquid… or granular materials (like sand)
- 3. Density, pressure Density: Pressure: Units: m ρ= V Pure water:1000 kg/m3 F⊥ p= A Pascal (Pa) = 1 N/m2 psi (pounds per square inch) atmosphere bar 1 atm = 1.013 × 10 5 Pa 1 bar = 105 Pa
- 4. Atmospheric pressure The atmosphereof Earth is a fluid, so every object in air is subject to some pressure. At the surface of the Earth, the pressure is patm ~ 1.013 x 105 Pa = 1 atm Area of a hand ~ 200 cm2 = 0.02 m2 F = patmA ~ 2000 N on your hand due to air! DEMO: Piston and weight
- 5. DEMO: Plastic tube with cover Pressurevs. depth Imaginary box of fluid with bases of area A and height h Ftop Net force must be zero! Fbottom = Ftop + mg Pbottom/top = m = ρAh h mg Fbottom Fbottom/top A pbottom = ptop + ρ gh Example: How deep under water is p = 2 atm? pbottom − ptop 1.01 × 105 Pa h= = = 10.3 m 3 3 2 ρg 10 kg/m 9.81 m/s ( )( ) (ie, 1 atm is produced by a 10.3 m high column of water)
- 6. DEMO: ascal’s vases Fluid inan open container Pressure is the same at a given depth, independently of the container. y Fluid level is the same everywhere in a connected container (assuming no surface forces) If liquid height was higher above A than above B pA > pB Net force → p(y) • A Net flow → • B This is not equilibrium!
- 7. DEMO: U-tube with water and kerosene ACT:U tube Two liquids Y and G separated by a thin, light piston (so they cannot mix) are placed in a U-shaped container. What can you say about their densities? A. ρG < ρY h1 Y G h2 • A B. ρG = ρY h3 • B C. ρG > ρY Pressure at A and B must be the same: ρ Y gh1 + ρG gh2 + patm = ρG gh3 + patm ρ Yh1 = ρ G ( h3 − h2 ) Since h1 < h3 − h2 ⇒ ρ Y > ρG
- 8. Water towers Water towersare a common sight in the Midwest… because it’s so flat! h phouse = patm + ρwaterhg
- 9. So physics sucks,but how much? Your physics professor sucks on a long tube that rises out of a bucket of water. She can get the liquid to rise 5.5 m (vertically). What is the pressure in her mouth at this moment? xB h A. 1 atm B. 0.67 atm x A C. 0.57 atm D. 0.46 atm E. 0 atm DEMO: Sucking through a hose pmouth + ρwater gh = patm pmouth = patm − ρwater gh = 105 Pa − ( 103 kg/m3 ) ( 9.8 m/s2 ) ( 5.5 m ) = 46100 Pa = 0.46 atm
- 10. Pascal’s principle Any changein the pressure applied to an enclosed fluid is transmitted to every portion of the fluid and to the walls of the containing vessel. Pascal’s Principle is most often applied to incompressible fluids (liquids): Increasing p at any depth (including the surface) gives the same increase in p at any other depth
- 11. Hydraulic chamber F1 F1 F2 = A1A2 A2 F2 = F1 A1 d2 F2 can be very large… d1 A1 No energy is lost: A1 W = F1d1 = F2 A 2 A2 ÷ d2 ÷ A 1 F2 ÷ = F2d2 ÷ Incompressible fluid: Ad1 = A2d2 1 A2
- 12. ACT: Hydraulic chambers Ineach case, a block of mass M is placed on the piston of the large cylinder, resulting in a difference di between the liquid levels. If A2 = 2A1, then: A. dA < dB dA A1 M A10 B. dA = dB C. dA > dB dB A2 M A10
- 13. Measuring pressure withfluids Barometer vacuum Vacuum p p=0 =0 Measures absolute pressure Barometer Top of tube evacuated (p = 0) atmosphere Bottom of tube submerged into pool of mercury Sample p=p at p0 open to sample (p) p Pressure dependence on depth: h = g ρHg Manometer Measures gauge pressure: pressure relative to atmospheric pressure. p − patm ∆h = Pressure dependence on depth: g ρHg A unit for pressure 760 mm Hg = 1 torr = 1 atm h h Manometer p1 p p atm p0atm ∆h ∆h
Editor's Notes
- #2 1a) Syllabus