Mechanical_properties Liquid

1 mechanical properties

1.1 volume
1.2 pressure , buoyancy
1.3 surfaces

1.3.1 free surface
1.3.2 level


1.4 flow
1.5 sound propagation

mechanical properties

volume

quantities of liquids measured in units of volume. these include si unit cubic metre (m) , divisions, in particular cubic decimeter, more commonly called litre (1 dm = 1 l = 0.001 m), , cubic centimetre, called millilitre (1 cm = 1 ml = 0.001 l = 10 m).

the volume of quantity of liquid fixed temperature , pressure. liquids expand when heated, , contract when cooled. water between 0 °c , 4 °c notable exception. liquids have little compressibility. water, example, compress 46.4 parts per million every unit increase in atmospheric pressure (bar). @ around 4000 bar (58,000 psi) of pressure, @ room temperature, water experiences 11% decrease in volume. in study of fluid dynamics, liquids treated incompressible, when studying incompressible flow. incompressible nature makes liquid suitable transmitting hydraulic power, because little of energy lost in form of compression. however, slight compressibility lead other phenomena. banging of pipes, called water hammer, occurs when valve closed, creating huge pressure-spike @ valve travels backward through system @ under speed of sound. phenomenon caused liquid s incompressibility cavitation. because liquids have little elasticity can literally pulled apart in areas of high turbulence or dramatic change in direction, such trailing edge of boat propeller or sharp corner in pipe. liquid in area of low pressure (vacuum) vaporizes , forms bubbles, collapse enter high pressure areas. causes liquid fill cavities left bubbles tremendous localized force, eroding adjacent solid surface.

pressure , buoyancy

in gravitational field, liquids exert pressure on sides of container on within liquid itself. pressure transmitted in directions , increases depth. if liquid @ rest in uniform gravitational field, pressure, p, @ depth, z, given by

p
=
ρ
g
z



{\displaystyle p=\rho gz\,}

where:

ρ



{\displaystyle \rho \,}

density of liquid (assumed constant)




g



{\displaystyle g\,}

gravitational acceleration.

note formula assumes pressure @ free surface zero, , surface tension effects may neglected.

objects immersed in liquids subject phenomenon of buoyancy. (buoyancy observed in other fluids, strong in liquids due high density.)

surfaces


surface waves in water

unless volume of liquid matches volume of container, 1 or more surfaces observed. surface of liquid behaves elastic membrane in surface tension appears, allowing formation of drops , bubbles. surface waves, capillary action, wetting, , ripples other consequences of surface tension. in confined liquid, defined geometric constraints on nanoscopic scale, molecules sense surface effects, can result in physical properties grossly deviating of bulk liquid.

free surface

a free surface surface of fluid subject both 0 perpendicular normal stress , parallel shear stress, such boundary between, e.g., liquid water , air in earth s atmosphere.

level

the liquid level (as in, e.g., water level) height associated liquid free surface, when s top-most surface. may measured level sensor.

flow

a simulation of viscosity. fluid on left has lower viscosity 1 on right

viscosity measures resistance of liquid being deformed either shear stress or extensional stress. in other words, viscosity resistance of liquid flow.

when liquid supercooled towards glass transition, viscosity increases dramatically. liquid becomes viscoelastic medium shows both elasticity of solid , fluidity of liquid, depending on time scale of observation or on frequency of perturbation.

sound propagation

the speed of sound in fluid given by

c
=


k

/

ρ




{\displaystyle c={\sqrt {k/\rho }}}

k bulk modulus of fluid, , ρ density. give typical value, in fresh water c=1497 m/s @ 25 °c.