29 Mar, 2013
Of a float
PRESENTATION: Archimedes’ principle establishes that if a body is totally or partially submerged in a fluid, then the fluid exerts a force upwards on the body that is equal to the weight of the fluid displaced by it.
- Two Experimental Approaches of Looking at Buoyancy, J. Agostinho Moreira, A. Almeida, and P. Simeão Carvalho, Phys. Teach. 51, 96 (2013)
- Just What Did Archimedes Say About Buoyancy?, Erlend H. Graf, Phys. Teach. 42, 296 (2004)
INTRODUCTION: Floatation is a well-known phenomenon: a body submerged in water appears to weigh less than in air. If the body is less dense than the fluid, it floats. A floating object is subject to two forces: its weight, which acts on the centre of mass; and a buoyant force, which acts on the centre of buoyancy, which is found at the geometric centre of the volume that is submerged.
OBJECTIVE: Verify the stability of an object in the face of several perturbations.
MATERIALS: a tray that is four or more centimetres deep, a beaker with a lid, a 20 cent coin.
SETUP: The tray is filled with water and coins are placed inside the plastic beaker and/or on the lid, depending on which experiment is to be carried out. Finally, the beaker is placed on the water and its stability can be checked.
EXPLANATION: The equilibrium of a floating object is stable if small perturbations in the state of the object make the buoyant force produce a moment of rotation to restore the object’s orientation and return it to the initial state of equilibrium. This happens if the centre of mass is located below the centre of buoyancy. If the object is barely stable, the centres of mass and buoyancy almost coincide. These concepts can be applied in the calculation of floatability for vessels, and how floatability will be modified when cargo is carried.
CONCEPTS: buoyancy, floatability, stability, centre of mass, Archimedes’ principle.
- SCHLUMBERGER EXCELLENCE IN EDUCATIONAL DEVELOPMENT
- UNIVERSIDAD AUTÓNOMA DE BAJA CALIFORNIA
- YOUTUBE 1
- YOUTUBE 2
- YOUTUBE 3
- Tipler P.A. Física, Reverté, 2010.
- De Juana J.M., Física General, Pearson, 2009.
- Serway R.A y J.W. Jewett. Física, Thomson-Paraninfo, 2010.
- R. Ehrlich, Turning the World Inside Out and 174 Other Simple Physics Demonstrations, Princeton University Press, 1997.
STUDENTS 2011-2012: Silvia Diz, Alejandra Victoria Dubra, María Durán, Sonia Fariña
LINK pdf STUDENTS (in Spanish):