In: Civil Engineering

compare the apparent specific gravity of the glass to its unit weight. Which is greater? and why

**Unit
weight**

Unit weight is also known as specific weight, is the weight of substance in a single volume unit.

it can be calculate by using the formula.

................(equation 1)

is the specific weight or unit weight of the material (weight per
unit volume,N/m^{3} )

is the density of the material (mass per unit volume,
kg/m^{3})

is acceleration due to gravity (rate of change of velocity, given
in m/s^{2}, and on Earth = 9.81
m/s^{2})

where the density of the material can be find out as

*where * is the mass, and
is the
volume of the material

apply this in equation 1

so unit weight is .....................(equation 3)

**Apparent specific
gravity**

specific gravity is the ratio of the weight of a volume of the
substance to the weight of an equal volume of the reference
substance.The reference substance is taken as water at its densest
point (at 4 °C or 39.2 °F) which is **1000
kg/m ^{3}** or

specific gravity =ρ_{material} /
ρ_{water}

if we take water as reference material ρ_{water}
is **1g/cm ^{3}**

specific gravity =ρ_{material} /1 =
ρ_{material}

_{Specific
gravity=}ρ_{material= }

but it may contain water-permeable voids.so apparent specific gravity is calculated on the basis of the net volume of material , that is the volume excluding water-permeable voids

Apparent specific gravity = ......................(equation 3)

is the dry mass of the material and is the the net volume of the material excluding volume of absorbed matter

so unit weight of material is from equation 1

and apparent specific gravity is from equation 3

(dry mass of the material) and (net volume of the material excluding volume of absorbed matter) is differ by a small amount so it is nearly equal to which is density of the material from equation 1.

So the **unit weight of the material =specific gravity*
** **≈
apparent specific gravity* **

*It is clear that for any material unit weight of the
material is greater than specific gravity by (acceleration due to
gravity)*

**For glass material** the density is 2500
Kg/m^{3} or 2.5 g/cm^{3} density of water is 1000
Kg/m^{3} or 1 g/cm^{3}

Apparent specific gravity=ρ_{glass} / ρ_{water}
==
**2.5** (unitless)

and unit weight = **specific gravity* =2.5 *9.81=24.525
kN/m ^{3}**

From these it is clear that the unit weight of the glass is
higher than specific weight by a value of g (9.81m/s^{2})
.It is because unit weight of any material is specific gravity
times acceleration due to gravity.

Define mass density and specific weight.
Define specific volume.
Define specific gravity.

Enumerate 1 liquid and 1 solid which have a specific gravity
(a) greater than 1 (b) less than 1
Your answer

1 a) How is density , specific gravity and specific weight
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1 b) How does density, vapour pressure and viscosity change with
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Take the density of the crown to be \(\rho_{\mathrm{c}} .\) What is the ratio of the crown's apparent weight (in water) \(W_{\text {apparent }}\) to its actual weight \(W_{\text {actual }} ?\)
Express your answer in terms of the density of the crown \(\rho_{\mathrm{c}}\) and the density of water \(\rho_{\mathrm{w}}\)
\(\frac{W_{\text {apparent }}}{W_{\text {actual }}}=1-\frac{\rho_{w}}{\rho_{c}}\)

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