Forces Within Objects At Rest Other “at Rest” Examples
Chapter 6: Forces in FluidsForces and motionObjects exert contact forces oneach other whenever andwherever they touchInside a material it can be normal,or sometimes sideways (shear), ifit is a solid.PS 110A Hatch Ch. 6 - 2PS 110A Hatch Ch. 6 - 3Forces within objects at restOther “at rest” examplesBlock inside monumentWeightacceleration 0net force 0Contact Forces1.2.3.4.Object hanging from a cable.Rubber ducky floating in tub.Helium balloon floating in air.Object at rest on the floor, but beingpushed on.A piece of an object at rest must haveinternal contact forces which balanceits weight.The net effect of these contact forces isupward.Net force acting on them?Washington MonumentPS 110A Hatch Ch. 6 - 4FluidPS 110A Hatch Ch. 6 - 5FluidConsider yourself floating on a lake.Fluid is a liquid or gas – it can flow. It cannotsupport sideways (shear) forces, when at rest.Is the earth pulling on you?There must be another force, a contact force,coming from the water.The net effect of that force is upward andbalances the gravitational force. Called buoyantforce.PS 110A Hatch Ch. 6 - 6pushes outward oncontainer (normal)When the fluid is at rest – forces must beperpendicular to any surfaces.Put ball in the water. The waterpushing at the bottom pushes inwhat direction?PS 110A Hatch Ch. 6 - 7
PressureLets talk about pressureFluid comes in contact with an object atmany points, so it is usually easier to talkabout pressure than the individual forces.Pressure ForceArea to which force is appliedCube of waterWeightContact Forcessteel block with nails (demo)Pressure DemoPS 110A HatchCh. 6 - 9PS 110A Hatch Ch. 6 - 8Pressure Force/AreaBounded vs. Unbounded Why do they not dothis when the person isstanding up? Why do they notuse just one nail?For a bounded fluid: Pressureapplied to any part of abounded fluid transmitsequally to every other partwith no loss.Demo: bed of nailsPS 110A Hatch Ch. 6 - 10PS 110A Hatch Ch. 6 - 11properties of pressureHydraulics Consider a blob of waterin an open (unbounded) tank of stillwater.P1: The net contact force pushing down on the blob isa) greater than the net contact force up on the blob.b) the same as the net contact force pushing up on the blob.c) less than the net contact force pushing up on the blob.PS 110A Hatch Ch. 6 - 12PS 110A Hatch Ch. 6 - 13
Analysis: immersed objects forces pushing up on the bottom ofthe object are greater than the thosepushing down on its top result: a net upward contact force,buoyancy– imagine static sphere of fluid not accelerating buoyant force must equal weight of fluid sphereRules for unbounded fluidbehaviorThe pressure of an unbounded fluid increaseswith depth, and is the same at all points atthe same depth, regardless of surface areaEach bit of fluid pushes outward,perpendicular to any surface or boundary contact force (pressure) mustincrease with depth,Demo: EP 12-2PS 110A Hatch Ch. 6 - 14Pressure increase depends on the fluiddensity.We live at the bottom of a fluidPS 110A Hatch Ch. 6 - 15Pressure in fluid 2P2: In which container is the pressure of the water– At sea level, air pressure is about 15 psiat the bottom the greatest? (depth same in both)Deep end of the swimming pool– Water pressure is about 1 atmosphere every 11 meters.Surface of Poolab(a) Container a(b) Container b(c) The same in bothDemo: evacuated canPS 110A Hatch Ch. 6 - 16Shape of containerPS 110A Hatch Ch. 6 - 17PressureDemo or video: E.P. 12-1 differentshapes (vessels)Method to measure water level in a tankThe pressure at a particular point is the same in alldirections, and always normal.Same pressure 1 inch below surface ofwater in a glass as in Utah Lake!Same wall strength needed to hold 10 ft deepwater in pool as 10 ft deep water in Lake Mead.PS 110A Hatch Ch. 6 - 18Video: E.P. 12-4PS 110A Hatch Ch. 6 - 19
Density: definitionhow dense will a material be?the density of an object is the ratio ofits mass to its volumedensity mass/volumeormass density x volumedensity is determined by the types of atomsin a material and how they are arranged atan atomic levelWhich is heavier, a ton of bricks or a ton offeathers? Which has a higher density?Two objects of the same size, will have differentweights if they have different densities.PS 110A Hatch Ch. 6 - 20Submerged objects in water (V(Vw V),all have same buoyant forcebuoyant forcesThe rule governing the buoyantforce is Archimedes' principle:– an object immersed in afluid experiences an upwardbuoyant force due to contactinteractions with thesurrounding fluid– the strength of the buoyantforce is equal to the weightof the fluid displacedPS 110A Hatch Ch. 6 - 21Eureka! Eureka!IronmgBWoodmgFg B net force downIf weight of object is greater thanweight of fluid displaced it will sink.Fg B net force upBWaterDemo: scale & immersed objects (rocks)PS 110A Hatch Ch. 6 - 22Archimedes studied floatingobjects in the public bathsWhat determines whether an objectwill float or sink?P3: Rubber ballsFg B remains stationaryPS 110A Hatch Ch. 6 - 23Archimedes’ PrincipleAccording to Archimedes’Archimedes’ Principle, an object willsink if its weight is greater than the weight of fluidit displaces.-How do volumes compare?-How do buoyant forces compare?-Must they both float? Or both sink?-What determines what will happen?What makes the Titanic float? Can I change density ofTitanic (or volume of fluid it displaces)?Demo: same size racket ballsDensity MassVolumeDemo: Aluminum TitanicPS 110A Hatch Ch. 6 - 24PS 110A Hatch Ch. 6 - 25
P4: How much water does ittake to float an aircraft carrier?Floating Objectsa)b)c)According to Archimedes Principle, an object will sink untilits weight equals the weight of displaced fluid.A few cupsA volume of waterequal to the volumeof the shipA weight of waterequal to the weightof the shipPS 110A Hatch Ch. 6 - 26Iceberg ExamplePS 110A Hatch Ch. 6 - 27float or sink?P5: What happens towater level if it snowson top of the iceberg?an object floats if its density is less thanthe density of the fluid it rests inan object sinks if its density is greater thanthe density of the fluid it rests inWhat happens to waterlevel if now the snowon top melts?demo: spheres in silica gel, diet and regular soda, ping pong ballIf you can change the object’s volume you maychange floats/sinks.PS 110A Hatch Ch. 6 - 28Ways to say something floatsIt is less dense than the surrounding fluid.It weighs less than an equal volume of fluid.The buoyant force is equal to its weight whenit is only partially submerged.It displaces a weight of fluid equal to its weightwhen it is only partially submerged.PS 110A Hatch Ch. 6 - 29Dense things sink.How dense is an egg? Will it float in plainwater?No!P6: What can I do to the water to makethe egg float?Demo: pseudo eggPS 110A Hatch Ch. 6 - 30PS 110A Hatch Ch. 6 - 31
Three CasesHow can water push up?1) Penny—An object more dense than the liquid—sinks.2) Ping Pong Ball—Object less dense than the liquid–floats.3) Dead man float—Object and liquid have the samedensity. The object is underwater but does not sink.Take a big breath and float higher. Let out air andfloat lower. This is howa submarine works.PS 110A Hatch Ch. 6 - 32Float or sinkIf I push on the ball it pushes backHow hard does it push?If I push down, the amount of ball underwater increases.The force pushing the ball up increases asthe volume of water displaced increasesForce pushing up Weight of displaced fluidBF (density of fluid) (volume of fluid displaced) (g)massDemo: Titanic kit (first not in the boat)water level as I put block in the boat?P7: What happens toPS 110A Hatch Ch. 6 - 33Freedom FestivalP8: Consider a long floating on a lake. Thebuoyant force on the log is(a) greater than(b) less than, or(c) equal to the weight of the log“Hot air rises.” Why?Hot air balloon can hover becausedensity of air will change with height.PS 110A Hatch Ch. 6 - 34PS 110A Hatch Ch. 6 - 35ConvectionConvectioncold (high density) fluids sinkwarm (low density) fluids risethis creates circulating currentscold (high density) fluids sinkwarm (low density) fluids risethis creates circulating currentsPS 110A Hatch Ch. 6 - 36PS 110A Hatch Ch. 6 - 37
Thought Question: ConvectionWhy is there no convection in fluids in anorbiting space shuttle?Hint: everything is in free fall, thus there is no contact force to balancegravitational pull (toward earth) (rememberthe scales in the elevator)--- so pressure doesn’t increase with depth.PS 110A Hatch Ch. 6 - 38
Chapter 6: Forces in Fluids PS 110A Hatch Ch. 6 - 3 Forces and motion Objects exert contact forces on each other whenever and wherever they touch Inside a material it can be normal, or sometimes sideways (shear), if it is a solid. PS 110A Hatch Ch. 6 - 4 Forces within objects at rest Blo
2 A. The forces shown above are PUSHING / PULLING forces. B. The forces shown above are WORKING TOGETHER / OPPOSITE FORCES. C. The forces are EQUAL / NOT EQUAL. D. The forces DO / DO NOT balance each other. E. The stronger force is pulling to the RIGHT / LEFT. F. The weaker force is pulling to the RIGHT / LEFT. G. Motion is to the RIGHT / LEFT. Circle the best answer on the line provided.
Forces Jacob Israelachvili ch 3,4 L6 Interaction forces- II Binnig, Quate, Gerber (reader) Intermolecular & Surface Forces Jacob Israelachvili ch 4,5 L5 Interaction forces-III Intermolecular & Surface Forces Jacob Israelachvili ch 5,6 Interaction forces-IV Intermolecular & Surface Forces Jacob Israelachvili ch 6,7 L7 F-Z, F-d curves – I
CHAPITRE I : STATIQUE DU SOLIDE 4. Bilan de forces 3.2. Forces concentrées forces réparties notion de centre de masse 3.3. Forces d’action forces de réaction 3.1. Forces extérieures forces intérieures 2. Conditions d’équilibre d’un solide 1. Définitions : force, solide, corps libre,
Hydrostatic Forces on Plane Surfaces Static Surface Forces Forces on plane areas Forces on curved surfaces Buoyant force Stability of floating and submerged bodies Forces on Plane Areas Two types of problems – Horizontal surfaces (pressure is
meaningful, and competitive. A marketing environmental scan looks at demographic forces, socio-cultural forces, economic forces, technological forces, competitive forces, and regulatory forces. A. Demographic Forces The statistical study of populations is referred to as demographics. It looks at age, gender, ethnicity, income, and occupation.
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Cisco Nexus 1000V for VMware vSphere REST API Plug-in Configuration Guide, Release 5.x 13 Using the REST API Plug-in Increase max-port via REST. Cisco Nexus 1000V for VMware vSphere REST API Plug-in Configuration Guide, Release 5.x 14 Using the REST API Plug-in Feature History for Using the REST API Plug-in.
However, the machining of these typically difficult-to-cut materials poses a challenge for conventional manufacturing technologies due to the high tool wear. Abrasive water jet (AWJ) machining is a promising alternative manufacturing technology for machining difficult-to-cut materials,
