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Similar to Fluid Mechanics - - - - - Buoyancy.pptx
Fluid Mechanics - - - - - Buoyancy.pptx
- 1. Fluid Mechanics Lecture 4:Buoyancy ME12076 Dr Lee Nissim ln480@bath.ac.uk
- 2. Fluid statics These threelectures are focussed on ‘fluid statics’ (fluids that are not moving) as opposed to ‘fluid dynamics’, which together make up ‘fluid mechanics’. Last lecture, we looked at pressure This lecture we will look at buoyancy Next lecture we will look at forces on submerged bodies
- 3. Archimedes principle The upthruston a body is equal to the weight of the fluid displaced by the body weight of the body, ρb h3 g upthrust (weight of displaced fluid, ρf h3 g) The body will sink The body will float
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- 5. Example: Conical buoy Aconical buoy with a base radius of 0.5 m and height of 2.5 m has a mass of 180 kg and is moored in salt water to a long length of steel cable with a mass per unit length of 12.2 kg/m. The height of the buoy protruding from the water is 0.63 m. , is 1026 kg/m3 . Neglecting the buoyancy force on the cable, find the water depth, H.
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- 7. Compressible fluids e.g. air:density is a function of temperature (ideal gas) Hydrostatic pressure: Temperature, pressure and density are all related. z sea level
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- 11. Example: Weather balloon Aspherical balloon of 8 m diameter and mass 60 kg is filled with Helium and released from its mooring at sea level. Find the height to which the balloon will rise, assuming that the balloon does not stretch, and that the air obeys the international standard atmosphere: where , and = 288 K And , where =1.225 kg/m3 Take the density of helium, , to be 0.17 kg/m3 .
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- 13. Example: Ice cube Thedensity of ice is approximately 900 kg/m3 , so an ice cube will float with 10% of its volume above the water. As the ice melts, its density increases to that of water (1000 kg/m3 ), what happens to the water level? d
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- 15. Summary Archimedes’ principle tellsus that the upthrust on a body is equal to the weight of fluid displaced by the body In air, changes in hydrostatic pressure drive changes in density, which in turn drive changes in buoyancy force with altitude. You can now attempt Q1 – Q3 on Tutorial Sheet 2!
- 16. Fluid Mechanics Lecture 4:Buoyancy ME12076 Dr Lee Nissim ln480@bath.ac.uk