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Buoyancy, Density and pressure recap
- Density
- ρ = m/V
- Units
- 1000 kg/m3 = 1000 g/l = 1 g/cm3
- SI unites = kilogram per meter cubed
- kg/m3
- kg/m3
- Gaussian unit = gram per cubic
centimeter
- equivalent to a gram
per milliliter
- 1000 kg/m3 = 1 g/cm3 = 1g/ml
- 1000 kg/m3 = 1 g/cm3 = 1g/ml
- equivalent to a gram
per milliliter
- 1000 kg/m3 = 1000 g/l = 1 g/cm3
- m = mass. V = volume
- Units
- http://physics.info/density/ for
selected densities
- The 'compactedness' of an object
- Materials have density It has no direction. Mass
in a continuous system
- Materials have density It has no direction. Mass
in a continuous system
- Specific gravity
- Unitless
- ratio of the density of a substance to
the density of a standard substance.
- standard
substance
- Water
- density of liquid water under
typical conditions on earth is
approximately 1000 kg/m3
- Soilds
- Liquids
- Relative density
- The ratio of substance to the density of the water at 4C
- No units (because it is a ratio
- No units (because it is a ratio
- The ratio of substance to the density of the water at 4C
- density of liquid water under
typical conditions on earth is
approximately 1000 kg/m3
- Gasses
- Air
- density of air at room
temperature near the
surface of the earth is
approximately 1.2
kg/m3.
- density of air at room
temperature near the
surface of the earth is
approximately 1.2
kg/m3.
- Air
- Water
- standard
substance
- Unitless
- To make something less dense you need to make the mass smaller or the volume bigger
- ρ = m/V
- Pressure
- P = F / A
- The force exerted per unit area
- kgm/s2 /
m2 =
kilograms
per meter
per
second2
- kg / ms2
- Units
- pascal (Pa)
- 1 atm = 1.013 x 10^5 Pa
- Patm = atmospheric pressure
- Patm = atmospheric pressure
- 1 atm = 1.013 x 10^5 Pa
- N / m2 = Newtons per m2
- 1 bar = 10^5 Pa
- pascal (Pa)
- The force exerted per unit area
- http://physics.info/pressure/
for selected pressures
including blood pressure etc
- various types
- Gauge pressure
- measured relative to atmospheric pressure. 0
means there is no pressure inside the gauge
compared to the atmospheric pressure on the
outside
- Negative gauge
pressure is also
called vacuum
pressure
- Measured using a manometer
- Pressure is dependent on depth
- http://www.efunda.com/formulae/fluids/manometer.cfm
- Monometer pressure
- p- p(atm) / g x density x height
- http://www.efunda.com/formulae/fluids/manometer.cfm
- Monometer pressure
- Pressure is dependent on depth
- measured relative to atmospheric pressure. 0
means there is no pressure inside the gauge
compared to the atmospheric pressure on the
outside
- Absolute pressure
- Pressure in relative to a perfect vaccum
- Equal to gauge pressure +1 atmosperic pressure
- Equal to gauge pressure +1 atmosperic pressure
- Measured using a barometer
- Pressure in relative to a perfect vaccum
- Differential pressure
- The difference in pressure of 2 points
- The difference in pressure of 2 points
- Gauge pressure
- Pascals principle
- Most often
applied to
incompressible
fluids
- http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html - pascals
principle and hydrolics
- any change of pressure of a contained liquid is distributed evenly
- Hydrstatic pressure
- Blaise Pascal 1623 - 1662
- Most often
applied to
incompressible
fluids
- Pressure is the ratio of force times area
- Continuous system
- Continuous system
- P = F / A
- Density and buoyancy
http://www.tclauset.org/20_ESbk/ch05.pdf
- Buoyancy
- Archimedes (287 - 212 BC)
- Father of Forensics
- Archimedes Principle
- The weight of fluid displaced in a body of water is equal to the
buoyant force on an immersed object
- When an object is partially or toatllly emersed in fluid it experienes
an upthrust that equal to weight of fluid displaced
- Upthrust (buoyancy) F(b)
- Force acting upward
that reduces the weight
of the object
underwater
- Apparent weight : measured when immersed in fluid
- Apparent weight : measured when immersed in fluid
- bouyant force is equal to the apparant weight loss
- Effect on object in fluid
- F(b) > W
- object will rise
- object will rise
- F(b) = W
- Object will float
- Weight of fluid displaced = weight of the object
- Weight of fluid displaced = weight of the object
- Object will float
- F(b) < W
- Object will sink
- Volume of liquid displaced = weight of object
- Volume of liquid displaced = weight of object
- Object will sink
- F(b) > W
- Force acting upward
that reduces the weight
of the object
underwater
- Upthrust (buoyancy) F(b)
- When an object is partially or toatllly emersed in fluid it experienes
an upthrust that equal to weight of fluid displaced
- EXAMPLES and applications
- Hydrometer
- measures relative density of liquids
- Tube containing lead shots in a bulb at the end (to weigh it down) enough for it to float vertically
- less dense
- larger volume of water must re displaced for bouyant force to equalize
- more hydrometer is submerged
- more hydrometer is submerged
- larger volume of water must re displaced for bouyant force to equalize
- more dense
- smaller volume of water must be displaced for buoyant forces to equalize
- less hydrometer submerged
- less hydrometer submerged
- smaller volume of water must be displaced for buoyant forces to equalize
- measures relative density of liquids
- Submarine
- Sinking
- Ballast tanks fill with water so that
the weight of the submarine is larger
than the volume of water displaced
- Ballast tanks fill with water so that
the weight of the submarine is larger
than the volume of water displaced
- rising
- ballast tank fills with air to make
the weight of the submarine
lsmaller than the volume of water
displaced
- ballast tank fills with air to make
the weight of the submarine
lsmaller than the volume of water
displaced
- Sinking
- Hot air balloon
- Ship
- A ship will float because it has a large
buoyant force acting upon it despite
being crafted of metal (which has a
larger density than water. The shape is
hollow so that the overall density will
be less than the density of the fluid it is
in
- Immersion variation
- Effect of temprature on object submersion
- warm water is more buoyant than cold is
that its molecules have more energy and
are moving around more. This makes
warm water less dense and it will rise
above denser, colder water.
- warm water is more buoyant than cold is
that its molecules have more energy and
are moving around more. This makes
warm water less dense and it will rise
above denser, colder water.
- Effect of liquid on submersion
- Salt water has a higher density
- Floating in the dead sea
- ship may sink further if it enters freshwater and is overloaded
- Floating in the dead sea
- plimsoll line
- indicates maximum weight
- indicates maximum weight
- Salt water has a higher density
- Effect of temprature on object submersion
- A ship will float because it has a large
buoyant force acting upon it despite
being crafted of metal (which has a
larger density than water. The shape is
hollow so that the overall density will
be less than the density of the fluid it is
in
- Hydrometer
- The weight of fluid displaced in a body of water is equal to the
buoyant force on an immersed object
- Had a Eureka moment when he
observed that the level of the
water in his bath increased when
he got in and realized he felt
lighter and used it to discover
the quality of the crown of King
Hiero II of Syracuse
- Density of gold, 19.32 g/cm3
Density of silver 10.5 g/cm3
- if a certain weight of
silver had been
substituted for the same
weight of gold, the crown
would occupy a larger
space than an identical
one of pure gold.
- Density of gold, 19.32 g/cm3
Density of silver 10.5 g/cm3
- http://www.physics.arizona.edu/physics/gdresources/documents/13_Archimedes.pdf
- Father of Forensics
- Archimedes (287 - 212 BC)
Medienanhänge
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