Density, specific gravity

Question 1

Define Density

Answer 1

Density is the mass per volume

Question 2

Formula of Density and units

Answer 2

Density = Mass / Volume kgm3 (cubed)

or M = V X D

Question 3

Full Define Specific gravity /relative density and describe.

Answer 3

Ratio of the desity of a substance compared to the density of a reference substance normally of water for liquids and air for a gas.
Temp and pressure must be constant.

In Physics specific means ratio

Substances with a specific gravity of 1 are neutrally buoyant in water, those with SG greater than one are denser than water,will sink in it, and those with an SG of less than one are less dense than water, and so will float.

Mercury 13.6 g/cm³

Question 4

Formula of specific gravity/relative density

Answer 4

SG = density of a substance/ density of water

Question 5

why is Understanding density is extremely important for a

firefighter

Answer 5

the density of a gas or
vapour determines whether it will tend to rise or
sink in air, and be found in the greatest concentrations
at the upper or lower levels in a building. The
density of a burning liquid partly decides whether
it is possible to cover it with water to extinguish
the fire, or whether the firefighter will need to use
foam or other another extinguishing medium.
However, another important factor is how well the
burning liquid mixes with water, a property known
as miscibility.

Question 6

what is vapour density normally compared to

Answer 6

the
density of a gas or vapour (vapour density, usually
abbreviated to VD) is given in relation to the
density of an equal volume of hydrogen, air or
oxygen under the same conditions of temperature
and pressure

For fire service purposes it is much more convenient
to compare the density of gases and vapours
with that of air. The reference gas should always
be given to avoid confusion: for example, the
vapour density of methane is 0.556 (air = 1), or 8
(hydrogen =1).

Question 7

what as a firefighter must be remembered about vapour densities of gases

Answer 7

However, differences in density
will affect the way in which they mix. Thus,
methane (the main component of natural gas) is a
light gas with a vapour density of about 0.5 (air =
1). If it is leaking into a room from a faulty gas
appliance, it will rise to the ceiling, entrainin(mixing with) air as it rises to form a layer of
methane and air mixture which will eventually
descend to the level of the leak. (The concentration
of methane in the layer will increase as the layer
descends.) On the other hand, a leak of propane
from a propane cylinder will produce a layer of
propane/air mixture at low level in a similar fashion,
as the vapour density of propane is roughly
1.5 (air= 1).g air

Question 8

State some examples of vapour density

Answer 8

Methane .5
Ethane 1.04
Propane 1.5
Butane 2

Question 9

State some examples of specific gravity

Answer 9

Balsa wood .2
water 1
Iron 7
Mercury 13