Density and Buoyancy Lab - University of Michigan



Instructor Outline: UM Physics Demo Lab 07/2013Density, Buoyancy andArchimedes’ PrincipleLab length: 70 minutesLab objective: To demonstrate the concepts of density, buoyancy, Archimedes’ Principle and surface tension.MaterialsDedicated Components:8 bent forks 8 paper clips8 Petri dishes8 brass blocks8 aluminum blocks8 wood blocks8 Teflon rods8 wood rods8 aluminum rods8 film canisters8 portions of fine sand8 plastic spoons8 graduated cylinders8 digital gram scales8 calculators8 cut-off 2 liter soda containers (vessels for floating film canisters)8 clear plastic rulers16 paper coffee filters (sand containment)Shared Components:soapy waterpaper towelsvacuum cleaner for sand cleanupSuggested Demonstrations:2B40.14 Archimedes' Principle 2B40.30 Cartesian Diver 2B40.u2 Buoyancy - Coke and Diet CokeMembrane stretched over the mouth of a vessel.Surface tension powered boat.Introduction: 5 minutes-LectureThe concept of density is defined.Exploration stage: 25 minutes – group lab-workThe students measure the mass and dimensions of some material samples. They calculate volume and density for these objects predict, and then test, their buoyancy in Dennison water.Analysis stage: 5 minutes – LectureArchimedes’ Principle is stated formally and demonstrated. The relative density criterion for floating/sinking in a fluid as a consequence of Archimedes’ Principle is presented.Application stage: 10 minutes – Group Lab-WorkThe students measure the volume of the submerged portion of a film can partially filled with sand and estimate the mass of the displaced water for the floating can. They compare the weight of the water with the weight of the can and verify Archimedes’ principle. They then draw a Free Body Diagram illustrating the film can floating in equilibrium.Exploration Stage: 15 minutes-Group Lab WorkThe students float paper clips on water and observe that soap disrupts surface tension and causes the paper clip to sink.Summary: 10 minutes – Lecture/Group DiscussionThe concepts of density and buoyancy as defined by Archimedes’ Principle are reviewed. The density criterion for floating/sinking/neutral buoyancy is reviewed. The analogy between surface tension and a stretched rubber membrane is presented and the ecological implications of soap contamination in lakes and streams are discussed.Concepts developed:Density is the ratio of mass to volume.Archimedes’ Principle.Density criterion for floating/sinking/neutral buoyancy.Free Body Diagram for a floating object.Surface tension.Disruption of surface tension by soaps and detergents. ................
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