Transcript Properties of Fluids

Properties of Fluids
How do ships float?
The answer is buoyancy
Buoyancy
The ability of a fluid, either gas or liquid, to exert
an upward force on an object
• Ships exert a force down onto the water
(weight)
• If the force pushing back (buoyancy) is greater
then the ship will float
• If the force pushing back is less, then the ship
will sink.
Archimedes’ Principle
• Buoyancy is equal to the weight of the water
displaced by an object
• If the weight of the water displaced is equal to
the object then it will float
• If the weight of the water displaced is LESS
than the weight of the object, then it will sink
Why does a wood block float and a
steel block sink?
The answer is Density
• If they are the same size or volume, they
displace the same volume and weight of
water.
• The buoyant forces would be equal for both.
• The answer is in the masses of the block.
If the water, wood and steel have different
masses but equal volumes, they must have
different densities!
• The density of the steel is greater than the
density of the water
• The density of the wood is less than the
density of the water
An object will float if it’s density is less
than the density of the fluid it is
placed in.
• If you formed the steel block into a hull and
filled it with air…
– It would have the same mass, but a greater
volume
– Density would decrease and the steel would float
– This is how ships float!
Balloon - The weight of the air displaced is
equal to the upward force and if greater than
the weight of the balloon the balloon will
accelerate upwards. If the weight of the
displaced air is less than the weight of the
balloon the balloon will accelerate towards the
ground.
Submarine - Able to travel on the surface of
the water or dive at will. Diving is
accomplished by special ballast tanks with
water, increasing the weight of the submarine.
To rise the water is forced out of the tanks
using compressed air.
Pressure
• Force exerted per unit area
• P=F/A
Pascal’s Principle
• A property of fluids (gases and
liquids) that states:
–Pressure applied to a fluid is
transmitted throughout the fluid
Hydraulic Lifts:
a pipe filled with fluid connects a
large and small cylinder.
Pressure applied to the small cylinder
is transferred through to the large
cylinder
Bernoulli’s Principle
As the velocity of a fluid increases,
the pressure exerted by the fluid
decreases
• The more pressure exerted on a fluid the less
velocity.
• Water will move faster through a narrower
pipe than it will through a wider pipe because
of pressure difference
Ex: Bernoulli’s principle
• The airplane wing is designed so that the top is curved and
the bottom is flat.
• Taxiing down the runway, the air blowing over the top of
the wing travels faster than the air blowing underneath.
• The faster air has a lower pressure, so the greater pressure
on the bottom of the wing pushes the plane up.
• When it gets going fast enough this lifting pressure exceeds
the downward gravitational force. The plane soars.
Viscosity
Resistance of a fluid to flow
• Low viscosity = flows easily
• High viscosity = flows slowly (resistant to flow)
• When a fluid begins to flow, the flowing
particles transfer energy to the stationary
particles.
• This causes them to flow, too.
• If flowing particles do not effectively PULL
other particles into motion then the viscosity
is high
• If the flowing particles DO effectively pull the
other particles into motion, then the viscosity
is low.