# Buoyancy, Density and pressure recap

Mind Map by Milly Kay, updated more than 1 year ago
 Created by Milly Kay over 5 years ago
100
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### Description

Forensic Science and profiling course Mind Map on Buoyancy, Density and pressure recap, created by Milly Kay on 11/02/2014.

## Resource summary

Buoyancy, Density and pressure recap
1 Density
1.1 ρ = m/V
1.1.1 Units
1.1.1.1 1000 kg/m3 = 1000 g/l = 1 g/cm3
1.1.1.2 SI unites = kilogram per meter cubed
1.1.1.2.1 kg/m3
1.1.1.3 Gaussian unit = gram per cubic centimeter
1.1.1.3.1 equivalent to a gram per milliliter
1.1.1.3.1.1 1000 kg/m3 = 1 g/cm3 = 1g/ml
1.1.2 m = mass. V = volume
1.2 http://physics.info/density/ for selected densities
1.3 The 'compactedness' of an object
1.3.1 Materials have density It has no direction. Mass in a continuous system
1.4 Specific gravity
1.4.1 Unitless
1.4.2 ratio of the density of a substance to the density of a standard substance.
1.4.2.1 standard substance
1.4.2.1.1 Water
1.4.2.1.1.1 density of liquid water under typical conditions on earth is approximately 1000 kg/m3
1.4.2.1.1.2 Soilds
1.4.2.1.1.3 Liquids
1.4.2.1.1.4 Relative density
1.4.2.1.1.4.1 The ratio of substance to the density of the water at 4C
1.4.2.1.1.4.1.1 No units (because it is a ratio
1.4.2.1.2 Gasses
1.4.2.1.2.1 Air
1.4.2.1.2.1.1 density of air at room temperature near the surface of the earth is approximately 1.2 kg/m3.
1.5 To make something less dense you need to make the mass smaller or the volume bigger
2 Pressure
2.1 P = F / A
2.1.1 The force exerted per unit area
2.1.2 kgm/s2 / m2 = kilograms per meter per second2
2.1.3 kg / ms2
2.1.4 Units
2.1.4.1 pascal (Pa)
2.1.4.1.1 1 atm = 1.013 x 10^5 Pa
2.1.4.1.1.1 Patm = atmospheric pressure
2.1.4.2 N / m2 = Newtons per m2
2.1.4.3 1 bar = 10^5 Pa
2.2 http://physics.info/pressure/ for selected pressures including blood pressure etc
2.3 various types
2.3.1 Gauge pressure
2.3.1.1 measured relative to atmospheric pressure. 0 means there is no pressure inside the gauge compared to the atmospheric pressure on the outside
2.3.1.2 Negative gauge pressure is also called vacuum pressure
2.3.1.3 Measured using a manometer
2.3.1.3.1 Pressure is dependent on depth
2.3.1.3.1.1 http://www.efunda.com/formulae/fluids/manometer.cfm - Monometer pressure
2.3.1.3.1.2 p- p(atm) / g x density x height
2.3.2 Absolute pressure
2.3.2.1 Pressure in relative to a perfect vaccum
2.3.2.1.1 Equal to gauge pressure +1 atmosperic pressure
2.3.2.2 Measured using a barometer
2.3.3 Differential pressure
2.3.3.1 The difference in pressure of 2 points
2.4 Pascals principle
2.4.1 Most often applied to incompressible fluids
2.4.2 http://www.grc.nasa.gov/WWW/k-12/WindTunnel/Activities/Pascals_principle.html - pascals principle and hydrolics
2.4.3 any change of pressure of a contained liquid is distributed evenly
2.4.4 Hydrstatic pressure
2.4.5 Blaise Pascal 1623 - 1662
2.5 Pressure is the ratio of force times area
2.5.1 Continuous system
3 Density and buoyancy http://www.tclauset.org/20_ESbk/ch05.pdf
4 Buoyancy
4.1 Archimedes (287 - 212 BC)
4.1.1 Father of Forensics
4.1.2 Archimedes Principle
4.1.2.1 The weight of fluid displaced in a body of water is equal to the buoyant force on an immersed object
4.1.2.1.1 When an object is partially or toatllly emersed in fluid it experienes an upthrust that equal to weight of fluid displaced
4.1.2.1.1.1 Upthrust (buoyancy) F(b)
4.1.2.1.1.1.1 Force acting upward that reduces the weight of the object underwater
4.1.2.1.1.1.1.1 Apparent weight : measured when immersed in fluid
4.1.2.1.1.1.2 bouyant force is equal to the apparant weight loss
4.1.2.1.1.1.3 Effect on object in fluid
4.1.2.1.1.1.3.1 F(b) > W
4.1.2.1.1.1.3.1.1 object will rise
4.1.2.1.1.1.3.2 F(b) = W
4.1.2.1.1.1.3.2.1 Object will float
4.1.2.1.1.1.3.2.1.1 Weight of fluid displaced = weight of the object
4.1.2.1.1.1.3.3 F(b) < W
4.1.2.1.1.1.3.3.1 Object will sink
4.1.2.1.1.1.3.3.1.1 Volume of liquid displaced = weight of object
4.1.2.2 EXAMPLES and applications
4.1.2.2.1 Hydrometer
4.1.2.2.1.1 measures relative density of liquids
4.1.2.2.1.2 Tube containing lead shots in a bulb at the end (to weigh it down) enough for it to float vertically
4.1.2.2.1.3 less dense
4.1.2.2.1.3.1 larger volume of water must re displaced for bouyant force to equalize
4.1.2.2.1.3.1.1 more hydrometer is submerged
4.1.2.2.1.4 more dense
4.1.2.2.1.4.1 smaller volume of water must be displaced for buoyant forces to equalize
4.1.2.2.1.4.1.1 less hydrometer submerged
4.1.2.2.2 Submarine
4.1.2.2.2.1 Sinking
4.1.2.2.2.1.1 Ballast tanks fill with water so that the weight of the submarine is larger than the volume of water displaced
4.1.2.2.2.2 rising
4.1.2.2.2.2.1 ballast tank fills with air to make the weight of the submarine lsmaller than the volume of water displaced
4.1.2.2.3 Hot air balloon
4.1.2.2.4 Ship
4.1.2.2.4.1 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
4.1.2.2.4.2 Immersion variation
4.1.2.2.4.2.1 Effect of temprature on object submersion
4.1.2.2.4.2.1.1 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.
4.1.2.2.4.2.2 Effect of liquid on submersion
4.1.2.2.4.2.2.1 Salt water has a higher density
4.1.2.2.4.2.2.1.1 Floating in the dead sea
4.1.2.2.4.2.2.1.2 ship may sink further if it enters freshwater and is overloaded
4.1.2.2.4.2.2.2 plimsoll line
4.1.2.2.4.2.2.2.1 indicates maximum weight
4.1.3 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
4.1.3.1 Density of gold, 19.32 g/cm3 Density of silver 10.5 g/cm3
4.1.3.2 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.
4.1.4 http://www.physics.arizona.edu/physics/gdresources/documents/13_Archimedes.pdf

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