Pressure and Fluid Flow Lab



Instructor Outline:UM Physics Demo Lab 07/2013 Pressure and Fluid Flow:Pascal and Bernoulli Lab length: 70 minutesLab objective: To demonstrate the concepts of pressure, compressible and incompressible fluids, hydrostatic pressure of a fluid column, continuity (mass conservation) in fluid flow, Pascal’s Principle, Pascal’s Law, gauge pressure, work and energy in a flowing fluid and Bernoulli effects due to the inverse relationship between flow speed and pressure in a moving fluid.Materials8 Bernoulli Tanks/Tubs8 aluminum rulers for tubs8 nylon plug (tank valves)8 Plastic Tubs – about 20” x 15” x 6”8 plastic storage box ramp supports (to aid in draining tubs)8 Homer buckets (to drain tubs)8 large Tygon drain tubes8 6’ Tygon Siphon tubes8 2’ Tygon tubes8 squeeze bulbs8 veterinary syringes8 plastic drinking cups8 plastic soda straws8 plastic coke bottles8 eye-droppers8 ?” cut steel washers8 hair dryers8 table tennis balls8 clear plastic rulers8 calculators8 sponges Shared Components:4 power stripsscrap paper2 sponge mopsragsOptional demonstrations at instructor’s request:2B30.30 Magdeburg Hemispheres 2B30.15 Pop Can Collapse 2C20.15-1 Venturi Tubes2C20.z -Fluid Dynamics Kit ("Bernoulli") Bottle of soda to simulate the rapid decompression of a scuba diverIntroduction: 5 minutes – LecturePressure is defined.Exploration Stage: 15 minutes – Group Lab WorkThe students explore atmospheric pressure and study how pressure differences can support a fluid column and drive fluid flow. Next they explore the difference between compressible air and incompressible water. Finally they demonstrate continuity (mass conservation) for water flowing out of the tank.Analysis Stage: 5 minutes – lectureAtmospheric pressure is defined and quantified. Large forces due to atmospheric pressure are demonstrated by passing around the evacuated Magdeburg spheres. Pascal’s Principle and Pascal’s Law are introduced. Continuity is formally defined.Application Stage: 10 minutes – group lab-workThe students construct a Cartesian diver and explain its operation using the concepts of pressure, density, compressibility and Pascal’s Principle.Analysis Stage: 5 minutes – LectureThe concepts of work and energy introduced in the context of a flowing fluid, stressing that the application of the Work-Energy Theorem to a drop of flowing fluid results in Bernoulli’s equation. The inverse relationship between fluid speed and pressure dictated by Bernoulli’s equation is introduced and demonstrated.Exploration Stage: 20 minutes – Group Lab WorkThe students next explore the consequences of energy conservation in a flowing fluid, first by comparing the motion of a horizontal stream of fluid to the motion of a horizontally launched projectile and then by considering energy conservation to relate the exit speed of the stream to the column height in the tank. The exit speed for fluid in a siphon is correlated with the column height driving the siphon flow. They discover that the depth the siphon inlet is submerged below the water surface does not affect the exit speed for the siphon.Application Stage: 5 minutes – Group Lab-WorkThe students trap a table tennis ball in the flow column from a hair drier and explain the effect using the inverse pressure-speed result from Bernoulli’s equation and the concept of force as the product of a pressure difference and the cross-sectional area of an object.Analysis and Summary Stage: 5 minutes – LectureThe results from the siphon experiment are reviewed and the work-energy relationships determining the observed flow behavior are discussed.Concepts developed:Definition of PressureCompressible and incompressible fluidsMass conservation (continuity) during incompressible fluid flow.Pascal’s Principle: Pressure is transmitted uniformly throughout a fluid and to the vessel walls.Pascal’s Law: The additional pressure due to a fluid column of height h is given by.Gauge pressure is the excess pressure relative to atmospheric pressure. The gauge pressure at a depth h in a fluid is therefore Application of the Work-Energy Theorem to a moving fluid yields Bernoulli’s equation.The exit speed for fluid from a hole or siphon is dictated by energy conservation and depends on the height of the fluid level above the exit hole.For a fluid flowing in a level pipe, Bernoulli’s equation, and hence energy conservation, dictates that pressure decreases as speed increases. ................
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