Density-Buoyant+Force-&-Archimedes's+Principle

__ Density, Buoyant Force and Archimedes’ Principle __

Civil War Connection: How much iron could an Ironclad float? In this activity you will investigate what makes objects float or sink, such as ships, submarines and hot air balloons.




 * [[image:SubmarineCrossSection.gif width="320" height="265"]] || [[image:TestTubeDiverFloatSink.png width="228" height="252"]] ||

Objects float if they are less dense than the fluid they are submerged in. Objects sink if they are denser than the fluid they are in. Objects with the same density as the fluid they are in are neutral in buoyancy. Determining whether an object will float or sink is done by comparing densities.

The buoyant force acts in the direction opposite to the force of gravity. In fluids, pressure increase with depth due to gravity. This results in a difference in pressure between the top and bottom of a submerged object. Due to the increasing pressure with depth, the force on the lower half of the object is greater than the force on the upper half of the object. Thus, the net force due to increasing pressure is in the upward direction, creating the buoyant force. Note that the arrow indicating pressure are longer lower on the object. Note how the dotted lines are closer together indicating more pressure.
 * [[image:Pressure Depth.png]] || [[image:hot-air-balloon-atmosphere.jpg]] ||

Archimedes’ Principle tells the strength of the buoyant force acting on an object. The buoyant force on a submerged object will equal the mass of the fluid displaced by the object (Archimedes' Principle). In math terms, buoyant force = the displaced fluid’s mass and also (Buoyant Force) = the (Fluid’s Density) x (Volume). This means that for an object to float, its mass must be not greater than the mass of the fluid it displaces. In other words, the mass of a floating object will equal the buoyant force acting on it.

Archimedes’ Principle can be investigated using a floating plugged-pipe. Due to this principle the (buoyant force) = (Density of the fluid) x (Submerged Volume). Because the mass of a floating object will equal the buoyant force, it follows that a floating objects’ (Mass) = (Density of the fluid) x (Submerged Volume) is also true by substitution. This second relationship can be rearranged to Mass /Volume = Density. From this we can see that the mass of a floating object divided by the submerged volume should always equal the density of the fluid. Procedure: 1. Measure the mass of the plugged-pipe. 2. Measure the mass of the plugged-pipe with the smaller mass inside it. 3. Measure the diameter of the plugged-pipe. 4. Determine the radius of the plugged-pipe. 5. Measure the submerged length of the floating, plugged-pipe. 6. Repeat steps 1 through 6 with the larger mass inside of the container. 7. Calculate the two submerged volumes of the plugged-pipe 8. Using the two weights and submerged volumes, calculate “submerged densities.” Analysis: 1. Explain how to use a balance and graduated cylinder to determine the density of water. Prove your explanation true. Cite your data. 2. When will an object float in a fluid? 3. How can whether an object will float or sink be determined? 4. Explain how the net forces on a submerged object results in a buoyant force? 5. What is Archimedes’ Principle? 6. How does the mass of a floating object compare to the buoyant force acting on it? 7. Calculate the buoyant force on the plugged-pipe with mass 1 and again with mass 2. 8. Determine if the mass of a floating object divided by its’ submerge volume equals the density of the fluid. Use a plugged-pipe and two different masses. Show your calculation for when each mass is floated in the pipe. 9. Calculate the volume of the whole cylindrical container. What mass of water could this volume displace? 10. What is the maximum weight that the plugged-pipe could float? Explain. Apply Archimedes' Principle.

Testing apparatus for this activity is shown bellow.

More http://www.pbs.org/opb/historydetectives/feature/civil-war-innovations/ http://learning.blogs.nytimes.com/2012/03/09/march-9-1862-the-monitor-and-merrimac-face-off-in-battle-of-hampton-roads/?_r=0 http://www.nbcnews.com/id/41056820/ns/technology_and_science-science/t/civil-war-ironclads-iconic-engine-gets-first-look/#.VRFzBPzF_sE http://www.georgiaencyclopedia.org/articles/history-archaeology/national-civil-war-naval-museum-port-columbus http://www.solarnavigator.net/inventors/john_ericsson.htm http://monitor.noaa.gov/publications/general/mon_brochure.pdf