# SC PHYS 201 - Buoyancy (2 pages)

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## Buoyancy

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## Buoyancy

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Lecture number:
24
Pages:
2
Type:
Lecture Note
School:
University Of South Carolina-Columbia
Course:
Phys 201 - General Physics I
Edition:
1
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Phys 201 1nd Edition Lecture 24 Outline of Last Lecture I Properties of materials and pressure Outline of Current Lecture II Pascal s Law III Buoyancy IV Balloons A Density at a given temperature Current Lecture Pascals Law t Pascal s law states that a change in external pressure of an enclosed fluid at rest at any point is equally transmitted to all points in the fluid As an equation this can be expressed as P P0 dgh P dgh Where P is the pressure d is the density of the fluid g is the force of gravity and h is the depth of the fluid For instance if you have a jug filled with some liquid then the pressure applied to the bottom of the jug is equal to the external pressure of the jug plus the pressure of the fluid dgh Buoyancy If you drop and object in water there will be pressure from the water on the top and the bottom of the object Below is a free body diagram of an object in water Pt PB mg Pt refers to the pressure of the water above the object which is pushing down on it P B refers to the pressure below the object pushing it upwards This is also known as buoyancy As shown in the free body diagram buoyancy works against the force of the weight of the object This means that if the These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute weight of an object is greater than the buoyancy the object will sink and if the weight of the object is less thank the buoyancy the object will float Whenever an object is submerged in a liquid there s a certain amount of liquid displaced The force of buoyancy is equal to the mass of this displaced liquid times the force of gravity The mass of the displaced liquid is equal to the density of the liquid times the volume of the liquid Equationally this is represented as FB mwg dhA g Balloons This same concept applies to gases Think about a floating balloon To make sure that the balloon floats the gas inside the balloon needs to be less dense than the air outside the balloon So what if you re trying to carry an object with the balloon Remember that mg dvg Therefore if you know the weight of the object you are trying to lift you can increase the volume of the balloon to accommodate the object Density at a given temperature The temperature of a gas can actually effect the density of the gas To figure out the density of a gas at a given temperature you need to first look up the density of that gas at 0 Plug this density into the following equation d d0 273 T 273 Where d is the density at the given temperature d o is the density at 0 C and T is the temperature in C

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