Transcript Buoyancy and Density

Buoyancy and Density
14-2
Buoyant 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 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
Determining 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
Cont….
• So…
– 1st determine
amount of liquid
displaced
– 2nd determine how
much that liquid
weighs
– 3rd weight =
buoyant force
Weight 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
Density and Floating
• Object is more
dense than its
surroundings =
sink
• Object is less
dense than
surroundings =
float
Math Focus! Page 415
• Complete 1, 2,3 on your paper
1. D = 25g ÷ 20cm3
1. D = 1.25 g/cm3
2. D = 546g ÷ 420cm3
1. D = 1.3 g/cm3
3. D = 163g ÷ 50cm3
1. D = 3.26 g/cm3
Determining 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.
Changing Overall Density
1. Changing shape can change densitysee page 417
2. Changing mass (ex.submarine)
3. Changing volume (ex. Swim bladder)