Physical properties various different terms

2.  Density
 Melting temperature

3.  The density, the volumetric mass density, of a
substance is its mass per unit volume.
 The symbol most often used for density is ρ

4.  The density of a material varies with
temperature and pressure.
 This variation is typically small for solids and
liquids but much greater for gases.
 Increasing the pressure on an object decreases
the volume of the object and thus increases its
density.
 Increasing the temperature of a substance
decreases its density by increasing its volume.
 In most materials, heating the bottom of a
fluid results in convection of the heat from the
bottom to the top, due to the decrease in the
density of the heated fluid. This causes it to
rise relative to more dense unheated material.

5.  Homogeneous materials
 The density at all points of
a homogeneous object equals its
total mass divided by its total volume.
 Heterogeneous materials
 If the body is not homogeneous, then its
density varies between different regions of
the object.

6.  Qn: Do you think the gold bars, gold chain
and gold coin have the same density?
 Ans: Yes, the density of a substance is a
constant that does not depend on its shape
or volume.
 Glass has a density of 2500 kg/m3. That
means 1 m3 of glass has a mass of 2500 kg.
 Silver has a density of 10.5 g/cm3. That
means 1cm3 of silver has a mass of 10.5 g.

7.  Qn : The density of Olive oil is 0.92 g/cm3. What is
the volume of 500 g of Olive oil?
Ans: Volume = mass / density = 500 / 0.92 = 544
cm3
 Qn: The mass of an empty beaker is 110 g. The total
mass of the beaker is 158 g when 50 cm3 of a liquid
is poured into it. What is the density of the liquid?
Ans: Density = mass / volume
= (158 – 110) / 50
= 48/50
= 0.96 g/cm3

8.  Qn: A room is 4 m long, 2.5 m wide and 2 m
high. If the density of air in the room is 1.3
kg/m3, what is the mass of air in the room?
Ans: Mass = density x volume
= 1.3 x (4 x 2.5 x 2)
= 26 kg

9.  Qn: Why is the woman
able to float in the dead
sea effortlessly?
 Ans: The density of dead
sea is very high (due to its
high salt content) and
human body is less dense
than the dead sea hence
she is able to float in the
dead sea.

10.  Qn: Why does normal coke
sink in water while diet coke
floats in water?
 Ans: Diet coke contains less
sugar than normal coke
hence its density is less.
Since it contains a lot of gas,
its density will be smaller
than that of water and will
float.

11.  Melting point, the temperature at which a
substance changes from solid to liquid state.

12.  The temperature at which a DNA double helix
dissociates into single strands
 Note that ‘melting’ in this sense is not a
change of aggregate state, but simply the
dissociation of the two molecules of the DNA
double helix.
 If a homogenous solution of identical double-
stranded DNA molecules is heated, the
strands dissociate increasingly at higher
temperatures

14.  At the melting point the solid and liquid
phase exist in equilibrium.
 The melting point of a substance depends on
pressure and is usually specified at standard
pressure.
 When considered as the temperature of the
reverse change from liquid to solid, it is
referred to as the freezing point or
crystallization point

15. Thank You