Liquids
Definite volume but no definite
shape!
Liquids
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Pressure
Buoyancy
Archimedes’ Principle
Density Effects
Pascal’s Principle
Pressure
• Pressure is the quotient of force exerted and
the area over which it occurs.
• P = F/A
• Pressure can also be thought of as the density
of a fluid acting at a certain depth.
• P = weight density X (depth)
• Both equations have units of N/m2 = Pascal
(Pa)
Pressure
• Total Pressure =
Wt. Density X Depth + atm.press
• Pressure of liquid does not depend on
amount of liquid, only its depth and wt.
density.
• Pressure does not depend on the shape of
the container.
Buoyancy
• A fluid (gas and/or liquid) will exert a force
on a submerged object.
– There is a net upward force - buoyant force
• This buoyant force depends on the wt.
density of the fluid and the volume of the
object submerged.
Buoyancy
• When the weight of a submerged object is
greater than the buoyant force, the object
will sink
– if the weight is less, object will float
– if the weight is equal, object will neither float
nor sink.
Buoyancy
• It turns out that the volume of fluid
displaced by the object is equal to the
volume of the object!
Archimedes’ Principle
• An immersed object is buoyed up by a force
equal to the weight of the fluid it displaces!
W apparent = W in air - F buoyant
• Immersed - either completely or partially
submerged
Because of this...
• If an object has a density < the density of
the fluid it is immersed in, it will
____________.
• If the object has a density > the density of
the fluid it is immersed in, it will
____________.
• Ans. Float ; Sink
Principle of Flotation
• A floating object displaces a weight of fluid
equal to its own weight.
• The volume of a submerged object is equal
to the
of liquid displaced.
• The weight of a floating object is equal to
the
of liquid displaced.
• Ans - volume, weight
Pascal’s Principle
• Blasé Pascal noticed that when a pressure
was exerted on an enclosed fluid, the
pressure was transmitted undiminished to
all points in the fluid and acted in all
directions.
• Thus, liquids are incompressible, and they
can be used to do work...
Applications of Pascal’s Principle
• Hydraulics
• Pneumatics
• Examples…
Archimedes’ Princ. Lab
• In this lab we will measure the buoyant
force and volume of several object
submerged in water.