Law of Flotation Relative density or Specific Gravity
It states that a floating object displaces its It is the ratio of the density (mass of a unit
own weight of the fluid in which it floats. volume) of a substance to the density of a
i.e. given reference material.
Weight of floating object = weight of It is a dimensionless quantity, as it is the
fluid displaced ratio of either densities or weights.
Mass of floating object = mass of fluid RD
subst an ce
Any changes in the density of the In SI units, the density of water is
surrounding liquid affects the level in (approximately) 1000 kg/m3 or 1 g/cm3,
which an object floats. which makes relative density calculations
particularly convenient: the density of the
Density (ρ) object only needs to be divided by 1000 or
1, depending on the units.
It is its mass per unit volume. The symbol
used for density is ρ. Viscosity (η)
V It is a fluid"s resistance to flow.
Where ρ is the density, m is the mass, and Fluids become less viscous as the liquid"s
V is the volume. temperature increases, becoming more
Its unit is kilograms per cubic meter viscous as the fluid gets cooler.
(kg/m3). A viscous fluid is sticky, thick and syrupy
If we take a cubic centimeter of some to a greater or lesser extent.
commonly known substances, we can see Its unit is the pascal second (Pa s)
that they weigh different amounts: 1 pascal second = 10 poise = 1,000
1 centipoise = 1 millipascal second
e.g. Treacle is quite viscous, but water is
not. Hot engine oil is less viscous
("thinner") and runs more quickly and
smoothly than cold engine oil.
So from the above examples it is easy to see
that some of the cubes weigh more than others, It states that a rise (fall) in pressure in a
even though they all take up the same amount flowing fluid must always be accompanied
of space. by a decrease (increase) in the speed, and
conversely, if an increase (decrease) in,
Entity ρ (kg/m3) the speed of the fluid results in a decrease
Interstellar medium (increase) in the pressure.
* Assuming 90% H, 10% 1×10−19 It states that Pressure energy + Kinetic
He; variable T energy + Datum or Potential energy =
The Earth (Mean density) 5,515 Constant
The Inner Core of the Earth 13,000 v2 p
The core of the Sun 33,000–160,000 gz constant , where:
Super-massive Black hole 9×105
v is the fluid flow speed at a point on a
White dwarf star 2.1×109
Atomic nuclei 2.3×1017
Neutron star 1×1018 g is the acceleration due to gravity,
z is the elevation of the point above a
Stellar-Mass Black hole 1×1018 reference plane, with the positive z-
direction pointing upward – so in the