physics part 1 mechanics physics 1700 fluids w. pezzaglia updated: 2013jul23
TRANSCRIPT
![Page 1: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/1.jpg)
Physics Part 1MECHANICSPhysics 1700
FLUIDS
W. Pezzaglia
Updated: 2013Jul23
![Page 2: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/2.jpg)
Fluids (Hydrostatics)
A. Pressure & Pascal’s Laws
B. Archimedes Principle
C. Surface Tension
2
![Page 3: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/3.jpg)
A. Pressure & Pascal’s Laws
Pascal’s Laws (1647)
1. Pressure defined
2. Hydraulics: Law of Transmitted Pressure
3. Law of Depth
3
Blaise Pascal1623-1662
![Page 4: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/4.jpg)
1. Pressure
(a) Definition: Force per area
(b) Units:– SI: Pascal=Newton/m2
– cgs: barye=Dyne/cm2
– Imperial: psi=pound/inch2
– Other: Torr=mm of Hg– Other: inches of Hg– Bar: millibar=100 Pascals
4
![Page 5: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/5.jpg)
2. Pascal’s Law of Pressure
• Transmitted Pressure: if the weight of a fluid is neglected the pressure throughout an enclosed volume will be the same
• the static pressure in a fluid acts equally in all directions
• the static pressure acts at right angles to any surface in contact with the fluid
• Major application is Hydraulics
5
Demo Breaking Bottle: http://www.youtube.com/watch?v=epOwdGIDzlY
![Page 6: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/6.jpg)
3. Law of Depth
• Pressure increases with (vertical) depth in a fluid of density :
P0 is atmospheric pressure at top of fluid, g is acceleration of gravity
6
ghPP 0
Water is shooting at faster at bigger depths due to more pressure
![Page 7: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/7.jpg)
3b. Pascal’s Vases7
Pressure is same at points A, B, C, D as the are at equal height
Pressure is same at bottom of these vases
![Page 8: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/8.jpg)
3c. Pascal’s Barrel
• Pascal's barrel was a hydrostatics experiment performed by Blaise Pascal in 1646. In the experiment, Pascal inserted a 10 m long (32.8 ft) vertical tube into a barrel filled with water. When water was poured into the vertical tube, Pascal found that the increase in pressure caused the barrel to burst.
• (Wikipedia)
8
![Page 9: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/9.jpg)
B. Archimedes Principle
287-212 BC
Discuss “the story of the crown”
9
![Page 10: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/10.jpg)
1. Buoyancy Force
• Objects weigh less in water
• Hence, there is an upward “Buoyant Force” on the object inside the fluid.
• If the Buoyant force is big enough, an object will “float”
10
![Page 11: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/11.jpg)
2. Archimedes's Principle (212 BC)
• “Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.”
11
![Page 12: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/12.jpg)
3. The Crown
• Can show ratio of (dry) weight “W” to Buoyant force “B” is equal to the specific gravity of the object.
• Compare “fake” crown with equal weight of real gold.
• Since “fake” crown has less density than real gold, its buoyant force is greater so they have different weights underwater
12
B
W
w
![Page 13: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/13.jpg)
4. Floating• Archimedes: “Any floating object
displaces its own weight of fluid.“
• If density of object is less than water, the buoyancy will exceed the weight and the object will rise to the surface.
• At the surface, the object will float such that the % of volume underwater equals its specific gravity.
• For example, specific gravity of ice is 0.917 so the ice cube in ordinary water will be 92% underwater and only 8% above. However, an iceberg relative to salty seawater (s.g. 1.025) will have: 0.917/1.025=0.895 or 89.5% underwater
13
![Page 14: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/14.jpg)
C. Surface Tension
1. Molecular Forces
2. Capillary Action
3. Surface Tension
14
![Page 15: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/15.jpg)
1. Molecular Forces
(a) Cohesion: tendency of similar or identical particles/surfaces to cling to one another
(b) Adhesion: the tendency of dissimilar particles or surfaces to cling to one another
15
![Page 16: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/16.jpg)
2. Capillary Action
(a) Capillary Rise whenadhesion>cohesion[water in glass tube]
(b) Capillary Depression whenadhesion<cohesion[mercury in glass tube]
16
![Page 17: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/17.jpg)
2c. Capillary Action
Capillary rise is greater in smaller diameter tube
17
![Page 18: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/18.jpg)
3. Surface Tension
(a) Cohesion makes surface of water behave like elastic membrane
(b) Objects with adhesion<cohesioncan float on surface
18
![Page 19: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/19.jpg)
3c. Surface Tension
• x
19
https://upload.wikimedia.org/wikipedia/commons/f/f8/Cutting_a_water_droplet_using_a_superhydrophobic_knife_on_superhydrophobic_surfaces.ogv
![Page 20: Physics Part 1 MECHANICS Physics 1700 FLUIDS W. Pezzaglia Updated: 2013Jul23](https://reader038.vdocuments.site/reader038/viewer/2022110321/56649cef5503460f949bd726/html5/thumbnails/20.jpg)
Notes/Demos
• PHET: Pascal's law of depth http://phet.colorado.edu/en/simulation/under-pressure
• PHET Density http://phet.colorado.edu/en/simulation/density
• PHET Buoyancy http://phet.colorado.edu/en/simulation/buoyancy
• PHET Buoyancy and Balloons http://phet.colorado.edu/en/simulation/balloons-and-buoyancy
20