The document discusses the concepts of density and relative density, detailing their definitions, measurements, and applications in the context of physical quantities and measurement. It outlines experiments for determining density and understanding the principles of floating and sinking based on density differences across states of matter. The document also includes numerical problems and evaluation questions relevant to the concepts introduced.

1. PHYSICS
CLASS : VIII
Chapter-2
PHYSICAL QUANTITIES AND
MEASUREMENT

2. CONCEPTS IN MODULE
 Density
Relative density
Floating and Sinking
Comparison of Densities in the three states of matter.
Numerical problems.
Glossary
Evaluation

3. INTRODUCTION
Measuring jar Measuring beaker Eureka can

4. How can you find the volume of irregular shaped solids?

5. Measurement of volume of irregular solids can be found using measuring cylinder.

6. What do you notice?
• Substances having density greater than water sink in it.
• Substances having density less than water float in it.

7. DENSITY

8. Density of a substance
• The density of a substance defines the amount of mass it contains in each
unit of its volume.
• It is the ratio of the mass of the substances (M) to the volume (V) occupied
by it.
Density D = Mass
Volume
SI unit of density : kg/m3

9. Every body has a certain mass and definite volume
Equal masses of different
substances have different
volume.
• For example
volume of cotton is greater than
volume of an equal mass of lead.
Equal volume of different
substances have different
masses.
• For example
Mass of iron is greater than the mass
of an equal volume of wood.

10. Density of a substance is independent of its shape or size.
 For example, the density of
aluminum is 2.7 g/cm3
Thus density of an article moulded
into different shapes but made of
pure aluminium will be the same.
 Density of water is 1 g/ cm3
Similarly, the density of water will
be the same even when it is taken in
a cup or in bottles of different
shapes or sizes.

11. ACTIVITY - 1

12. To determine the density of
irregular objects using
EUREKA CAN
 Take an eureka can and fill it with
water.
 Tie the solid (weigh it before use)
with a string and gradually dip inside
the can.
 The solid displaces the water which
is equal to its volume.
 Measure the volume.
 Calculate Density = mass/volume

13. RELATIVE DENSITY

14. Relative density

15.  Relative density is the ratio of the density of a substance to the density of water.
Density of a substance = density of a substance
density of water
It is also known as specific gravity.
It has no unit.
Density of water is 1000 kg/ m3 or 1 g/ cm3
If the relative density of a substance is known , density of the substance
can be found easily.

16. COMPARISON BETWEEN DENSITY
AND RELATIVE DENSITY
DENSITY
• It is defined as mass per unit
volume.
• Its value is different in different
systems of measurement.
• Its units are kg/m3 and g/cm3
RELATIVE DENSITY
• It is defined as the ratio of density
of a substance to the density of
water at 4°c.
• Its value is same in all system of
measurement.
• It has no units.

17. NUMERICAL PROBLEMS

18. • Q1. find the relative density of
kerosene. The density of kerosene is
810 kg/m3 and density of water is
1000 kg/m3
• Solution:
density of kerosene = 810 kg/m3
Density of water = 1000 kg/m3
Therefore,
RD of kerosene= 810/1000
= 0.81
• Q2. The relative density of iron is
7.87. Find the density of iron.
• Solution:
Relative density of iron = 7.87
Density of water = 1000 kg/m3
Density of substance =rd of substance x
density of water
Therefore,
Density of iron =7.87x 1000= 7870
kg/m3

19. FLOATING Or SINKING
(based on density)
https://www.youtube.com/watch?v=2dyCe1GPagE

20. Did you know?
(DENSITY)
ORANGES DEAD SEA
An orange
floats but
when
peeled off,
it sinks.
Why?
Why is it
easy to
float in
dead
sea?

21. ACTIVITY - 2

22. Activity:
To understand floating and sinking with respect to density
Case 1
• Conclusion: density of wood is less
than water. Density of iron is more than
water.
Case 2
• Conclusion: density of wood is
less than water. Density of wood is
more than kerosene.
Material : 2 beakers; water; iron nail ; kerosene; wooden block

24. ACTIVITY - 3

25. ACTIVITY:
To compare the density of
cooking oil and water
Material required:
1. Two glass bottles
2. Water
3. Cooking oil
Conclusion: The density of water is
more than the density of cooking oil.

26. TRY THIS
AT HOME
DENSITY TOWER

27. RELATIVE
DENSITY BOTTLE

28. It is a small thin bottle.
Also known as specific gravity bottle.
It is a bottle of fixed capacity
It has a glass stopper with a fine
hole.
Relative density of a liquid can be
found using it.
description

29. ACTIVITY - 4
(To find the relative density of a liquid usinf a relative density bottle)

30. • Mass of the liquid M (f) = M3-M1 = ________
• Mass of water M(w) = M2-M1 = __________
• Density of the liquid = mass(f)
volume
Density of water = mass (w)
volume
Relative density = density of the liquid
density of water
= _________________

31. COMPARISON OF
DENSITIES IN THE THREE
STATES OF MATTER

32. solid
• Less Intermolecular space
• Highly dense
liquid
• More intermolecular space
• Less denser
gas
• Much intermolecular space
• Least dense

33. Can density of a substance be changed?
Upon heating or cooling the density of a substance can be changed.
Particles
moves
away
expands
Volume
increases
Density
decreases
vibrates
Particles
Comes
close
contract
Volume
decreases
Density
increases
Vibrations
slow down
Upon
heating
Upon
cooling

34. CONVENTION

35. DEFINITION
It is a mode of heat transfer
through the movement of
particles in a substance.
Fluid
molecules
upon heating
Becomes
light &
Rises up
A less denser
substance
always floats
Cooler and
denser fluid
moves
downwards
The cooler
& denser
fluids gets
heated &
rises up
HOW CONVENTION TAKE PLACE?
This continuous circulatory motion of the fluid is known as convention current

36. Applications
Room heaters
Land breeze Sea breeze
House ventilators

37. RECAPTULATION
• The space occupied by a substance is known as volume.
• The capacity of any vessel to accommodate more amount of liquid is called holding
capacity.
• Measuring cylinder, beaker eureka can, etc. are used for measuring volume of liquid.
• Measurement of volume of regularly shaped solid can be found using formula.
• Measurement of volume of irregular solid can be found using eureka can.
• The density of a substance is defined as the mass per unit volume of a substance.
• The relative density is equal to the mass of the given volume of the substance divided by
mass of equal volume of water. This forms the basic principle of working of a density
bottle

38. EVALUATION

39. Fill in the blanks
1. The capacity of any vessel to accommodate more amount of liquid is called
its _________.
2. The volume of the solid substances is measured in ________.
3. The substance having density higher than that of water will _______ in
water.
4. Land and sea breeze is an application of ___________.
5. More the density ________ is the intermolecular space in the matter.

40. ANSWER THE FOLLOWING
1. Describe density.
2. How can we find the volume of an irregular shaped solid?
3. What is density bottle ?
4. What is the formula of relative density?
5. What is convention current?