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Buoyancy and DensityBuoyancy and Density
14-214-2
Buoyant ForceBuoyant Force
• Buoyant force = upward force that keeps an object immersed in or floating on a liquid
• It’s the force that pushes an ice cube up to the surface of water
• Buoyant force = upward force that keeps an object immersed in or floating on a liquid
• It’s the force that pushes an ice cube up to the surface of water
Buoyant Force and Fluid PressureBuoyant Force and Fluid Pressure
• Water exerts pressure all around an object
• Horizontally the pressures are equal and cancel each other out.
• Vertically, the deeper the object, the more pressure exerted
• The force pushing upward is the buoyant force
• Water exerts pressure all around an object
• Horizontally the pressures are equal and cancel each other out.
• Vertically, the deeper the object, the more pressure exerted
• The force pushing upward is the buoyant force
Determining Buoyant ForceDetermining Buoyant Force
• Archimedes was a mathematician who lived in 3rd century BCE and discovered a way to determine buoyant force.
• Archimedes's Principle = buoyant force is equal to the weight of the volume of fluid the object displaces
• Archimedes was a mathematician who lived in 3rd century BCE and discovered a way to determine buoyant force.
• Archimedes's Principle = buoyant force is equal to the weight of the volume of fluid the object displaces
Cont….Cont….• So…
– 1st determine amount of liquid displaced
– 2nd determine how much that liquid weighs
– 3rd weight = buoyant force
• So…– 1st determine
amount of liquid displaced
– 2nd determine how much that liquid weighs
– 3rd weight = buoyant force
Weight vs Buoyant ForceWeight vs Buoyant Force
• Object will sink if its weight is greater than the buoyant force acting on it
• Object will float if weight is equal to buoyant force
• Buoying Up = object under water is pushed up until the part under is equal to the amount it displaces
• Object will sink if its weight is greater than the buoyant force acting on it
• Object will float if weight is equal to buoyant force
• Buoying Up = object under water is pushed up until the part under is equal to the amount it displaces
Density and FloatingDensity and Floating• Object is more
dense than its surroundings = sink
• Object is less dense than surroundings = float
• Object is more dense than its surroundings = sink
• Object is less dense than surroundings = float
Math Focus! Page 415Math Focus! Page 415
• Complete 1, 2,3 on your paper1. D = 25g ÷ 20cm3
1. D = 1.25 g/cm3
2. D = 546g ÷ 420cm3
1. D = 1.3 g/cm3
• D = 163g ÷ 50cm3
1. D = 3.26 g/cm3
• Complete 1, 2,3 on your paper1. D = 25g ÷ 20cm3
1. D = 1.25 g/cm3
2. D = 546g ÷ 420cm3
1. D = 1.3 g/cm3
• D = 163g ÷ 50cm3
1. D = 3.26 g/cm3
Determining DensityDetermining Density
• Need mass and volume!• Volume of a regular solid = L*W*H
– (length*width*height)
• Volume of irregular solid = use displacement.– Measure volume of liquid , add object,
measure new volume, subtract to get volume of object.
• Need mass and volume!• Volume of a regular solid = L*W*H
– (length*width*height)
• Volume of irregular solid = use displacement.– Measure volume of liquid , add object,
measure new volume, subtract to get volume of object.
Changing Overall DensityChanging Overall Density
1. Changing shape can change density- see page 417
2. Changing mass (ex.submarine)3. Changing volume (ex. Swim
bladder)
1. Changing shape can change density- see page 417
2. Changing mass (ex.submarine)3. Changing volume (ex. Swim
bladder)