ICSE 8th Physics Notes

MATTER
Matter can be defined as anything that has both mass and volume and occupies a certain
space in the universe. Matter is composed of tiny particles called Molecules
The SI unit of mass is kilogram.
The CGS unit of mass is gram.
The FPS unit of mass is pound.
The SI unit of volume is cubic metre (m3).
Characteristics of Matter
The characteristics of particles of matter are as follows:
• The particles of matter have spaces between them.
• The particles of matter are in continuous motion.
• The particles of matter attract one another.
• Matter is made up of extremely small particles called atoms. Atom is the smallest possible
unit of matter that exhibits all the properties of that matter.
• When atoms combine with one another, minute particles are formed, which are called
molecules.
Inter-molecular force
The molecules of matter exert a force of attraction on each other. This force of attraction is
called inter-molecular force.
Solids
Here the molecules are very tightly packed that there is no or very less intermolecular
space and there is high intermolecular force of attraction (force of cohesion). The molecules
do not move about their mean position and thus solids have a definite shape and volume.
Liquids
Here the molecules are less tightly packed as compared to solids and also there is lesser
force of intermolecular attraction. The intermolecular distance is greater than that in the
solids. Thus, they do not have a definite shape but acquire the shape of the vessel in which
they are contained but have a definite volume at a given temperature.
Gases
Here the molecules are far apart from each other i.e. have the greatest intermolecular
distance which result into the weakest intermolecular forces of attraction. The molecules as
are not bound by any strong force, move about freely and thus gases do not have a definite
shape an also do not have any definite volume.
MELTING
The change from the solid state to the liquid state in heating at a fixed temperature is called
melting
MELTING POINT:
The temperature at which a solid starts changing into LIQUID without further increase in
temperature is called MELTING POINT.” Or The constant temperature at which a solid
changes into liquid.” Example : Ice (solid) melts at Q?C into water (liquid) when heated.
BOILING POINT :
The temperature at which a LIQUID start changing in vapour without further rise in
temperature.
Or
The constant temperature at which a LIQUID starts changing into GAS (vapours) Example :
Boiling point of water (liquid) is 100°C.
CONDENSATION :
The change of vapours on cooling at fixed temperature to liquid is called condensation.
Example: When water vapours at 100°C are cooled they change into water (liquid).
SUBLIMATION :
The process of change of solid directly into vapours on heating is called sublimation .
EVAPORATION :
The change of state of a liquid to vapour at all temperatures from the surface of liquid is
called evaporation.
Factors on which affect the rate of evaporation of a liquid:
(i) AREA OF EXPOSED SURFACE.
(ii) TEMPERATURE OF LIQUID.
(iii) NATURE OF THE LIQUID.
(iv) PRESENCE OF HUMIDITY.
Difference between Solid Liquid and Gases

Solids Liquids Gases
Highly Strong intermolecular forces The intermolecular forces are The intermolecular forces are
between the molecules, leads to a stronger than gases but weaker practically non-existent. Thus, there
definite volume in Solids. than solids. is no definite volume.
Liquids do not have a definite
Solids have a definite shape to them. Gases do not have a definite shape.
shape.
The intermolecular space between The intermolecular space is The intermolecular space is free-
solids is absent. moderate but present. flowing and plenty.
The force of attraction between the The force of attraction between There is no intermolecular force of
molecules is incredibly high. molecules is pretty moderate. attraction between the molecules.
Gases can be compressed quite
They are incompressible. Liquids cannot be compressed.
easily.
Solids have a definite shape and Liquids have a definite
Gases have no definite volume.
volume. volume.
Differences between Evaporation and Boiling

Evaporation Boiling
Evaporation is a normal process that occurs when the liquid Boiling is an unnatural process where the
form changes into the gaseous form; while causing an liquid gets heated up and vaporized due to
increase in the pressure or temperature. continuous heating of the liquid.
Boiling usually occurs on the entire mass of
Evaporation usually occurs on the heated liquid’s surface.
the liquid that gets heated up.
Bubbling effect is visible during the process of
Bubbling effect is not visible in evaporation.
boiling.
The process of evaporation is slow. The process of boiling is much quicker.
Physical Quantities and Measurement

Density
The density of a matter is the mass per unit volume present in it.
Density of a substance = Mass of Substance/Volume of the Substance
Formula d=M/V
SI unit for Density Kg m-3
CGS unit for Density g cm-3
The relative density of a substance is defined as the ratio of the density of the substance to
the density of water Or relative density of a substance can also be defined as the ratio of
the mass of any volume of the substance to the mass of an equal volume of water. Relative
Density is just a ratio , a number has no unit.
R.D. = Density of the Substance/Density of water
Or R.D. = Mass of any volume of the substance/Mass of the same volume of water
The density of a substance can change significantly when it transitions between different
states of matter: solid, liquid, and gas. Here’s how density typically varies with state
changes:
Solid State:
- Solids generally have the highest density among the three states of matter because their
particles are closely packed together in a fixed arrangement. This close packing leads to a
higher mass per unit volume.
Liquid State:
- When a solid melts into a liquid, its density usually decreases. This is because the particles
become less tightly packed compared to the solid state. However, there are exceptions; for
example, water is less dense as a liquid than as a solid (ice), which is why ice floats.
Gas State:
- Gases have the lowest density because their particles are much farther apart, resulting in
a lower mass per unit volume. When a liquid evaporates into a gas, the density decreases
significantly.
The buoyant force is the upward force on any object in any fluid. The buoyant force is equal
to the weight of the liquid displaced by the immersed part of the body.
 A body floats in a liquid if its less than the density of liquid.
 The body will sink if its density is more than the density of the liquid.
 The body will remain suspended if its density is equal to the density of the liquid.
Law of Floatation: The weight of the solid floating in a fluid is equal to the weight of the
fluid displaced by immersed part of the solid.
Volume of body × Density of body = Volume of displaced liquid × Density of liquid
Application of Floatation
The floating of ship on water
Ships generally are made of heavy metals which makes them denser than water but they
float on water because they contain a whole lot of air which makes their avg. density less
than that of water so they're able to float on water.
Hot air balloon
The air inside the balloon is heated by a burner to a temperature which makes it less dense
than the air outside of the balloon. As a result the balloon floats
Icebergs
Iceberg float because when water freezes it expands and the solid is less dense than the
liquid
FORCE and PRESSURE

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MATTER

Difference between Solid Liquid and Gases

Differences between Evaporation and Boiling

Physical Quantities and Measurement

FORCE and PRESSURE

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