5 - 18 Density and pressure
Density
3 m(mass[ g]) 3 m(mass[kg ])
● *** ρ( density [g / c m ])= 3 /
ρ( density [kg/ m ])= 3
V (volume [ c m ]) V (volume [m ])
● Anything made of same material will have same density (THEORETICALLY)
● Measure mass: mass balance
volume: measure with ruler (then ^3 sides)/Eureka can (for irregular objects -
displacement [of volume of water])
Pressure
F (force [N ]) 2 F (force [ N ])
● *** p( pressure[ Pa])= 2 /
p( pressure[ N /cm ])= 2
A (area[m ]) A (area[ cm ])
○ ***∴ 1 N/cm2 = 10000 Pa
●
● ***Uniform pressure: pressure acting on surface equally at all points
● Pressure in liquids and gases
○ ***Pressure at any point of liquid/gas AT REST acts equally in all directions
○ ***Liquid vs gas - gases are compressible while liquids are not
○
○ If pressure is greater in one region of fluid than another, fluid will flow until
pressure difference is equalised
■ ***Fluids always flow from regions of higher pressure to lower
pressure (unless pressure difference is SOLELY due to gravity, e.g.:
standing bottle of water)
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Density
3 m(mass[ g]) 3 m(mass[kg ])
● *** ρ( density [g / c m ])= 3 /
ρ( density [kg/ m ])= 3
V (volume [ c m ]) V (volume [m ])
● Anything made of same material will have same density (THEORETICALLY)
● Measure mass: mass balance
volume: measure with ruler (then ^3 sides)/Eureka can (for irregular objects -
displacement [of volume of water])
Pressure
F (force [N ]) 2 F (force [ N ])
● *** p( pressure[ Pa])= 2 /
p( pressure[ N /cm ])= 2
A (area[m ]) A (area[ cm ])
○ ***∴ 1 N/cm2 = 10000 Pa
●
● ***Uniform pressure: pressure acting on surface equally at all points
● Pressure in liquids and gases
○ ***Pressure at any point of liquid/gas AT REST acts equally in all directions
○ ***Liquid vs gas - gases are compressible while liquids are not
○
○ If pressure is greater in one region of fluid than another, fluid will flow until
pressure difference is equalised
■ ***Fluids always flow from regions of higher pressure to lower
pressure (unless pressure difference is SOLELY due to gravity, e.g.:
standing bottle of water)
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