## Monday

### physics note : fluids and solid material

density and specific gravity
density of an object is mass per unit volume
SI unit : kg/m3 (hahah ape aku tulis ni)
to convert g/cm3 to kg/m3 , multiply by 1000

the specific gravity of a substance is the ratio of its density to that of water

pressure in fluids
pressure is defined as force per unit area.
pressure is scalar. the SI unit for pressure is pascals. 1 Pa = 1 N/m2

pressure is the same in every direction in static fluid at given depth; if it were not, the fluid would flow.
for a fluid at rest, there is also no component of force parallel to any solid surface.

pressure at depth below the surface of liquid can be calculated by:
pressure = density x gravity x depth

Gauge pressure
pressure above the atmospheric pressure.

Absolute pressure
sum of the atmospheric pressure and the gauge pressure

Devices for measuring pressure :
manometer, aneroid gauge, tire pressure gauge, barometer

Archimede's principle:
the buoyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object.

if an object's density is less than that of water, there will be an upward net force on it, and it will rise until it is partially out of water.

FLOATING: force = upthrust + weight
SINKING : force = weight - upthrust

sphere : use Stoke's Law.
viscous drag + upthrust = weight

for a floating object, the fraction that is submerged is given by the ratio of the object's density to that of the fluid.

Fluids in motion; Flow rate and the equation of continuity
laminar flow : smooth flow of fluid, streamline.
turbulent flow : has eddies; at high speed.

Bernoulli's Principle
when the velocity is high, the air pressure is low, when the velocity is low, the air pressure is high. that's why aeroplane can fly.. oh that's why aeroplane can fly :)
(ini lagu famous masa dekat samura dulu. haha)

pressure + 1/2 density x velocity + density x gravity x jarak
(samakan equation 1 dengan equation 2)

viscosity : internal friction is real fluids. Stoke's Law.

the rate of flow in a fluid in a round tube depends on :
the viscosity of the fluid
the pressure difference
the dimensions of the tube

the volume flow rate is proportional to the pressure difference, inversely proportional to the length of tube and to the pressure difference, and proportional to the fourth power of the radius of the tube.

thanx.do come again.