Comprehensive study notes for Properties of Matter (Chapter ) Physics Matric 9th. Read detailed explanations, solve MCQs, practice questions with answers. Free online education Pakistan.
Postulates:
1. Matter is made up of particles called molecules.
2. These molecules remain in continuous motion.
3. Molecules attract each other.
Solids: Molecules are closely packed, vibrate about mean positions, rigid shape and volume.
Liquids: Molecules are less closely packed, can slide over each other, fixed volume but no fixed shape.
Gases: Molecules are far apart, move randomly at high speeds, no fixed shape or volume.
Plasma: The fourth state of matter, consisting of ions and electrons (ionized gas), found in stars.
Density: The mass per unit volume of a substance is called its density.
Formula: $Density = \frac{Mass}{Volume}$ or $D = \frac{m}{v}$
Unit: SI unit is kilogram per cubic metre ($kg m^{-3}$).
Architects and engineers consider the density of materials when designing structures to ensure stability and strength.
Definition: The force acting normally per unit area on the surface of a body is called pressure.
Formula: $P = \frac{F}{A}$
Unit: SI unit is $Nm^{-2}$ or Pascal (Pa).
Pressure is a scalar quantity.
The earth is surrounded by a cover of air called the atmosphere. The pressure exerted by this air column is called atmospheric pressure.
At sea level, $P_{atm} \approx 101,300 Pa$ or $1 atm$.
It is measured using a Barometer.
Statement: Pressure applied at any point of a liquid enclosed in a container, is transmitted without loss to all other parts of the liquid.
Applications: Hydraulic Press, Hydraulic Brakes, Hydraulic Jack.
A machine that works on Pascal's Law.
It consists of two cylinders of different cross-sectional areas $a$ and $A$.
Force $F_1$ applied on small piston produces pressure $P = F_1/a$.
This pressure is transmitted to large piston, producing force $F_2 = P \times A$.
$F_2 = F_1 \times \frac{A}{a}$. Since $A > a$, $F_2 > F_1$.
Statement: When an object is totally or partially immersed in a liquid, an upthrust acts on it equal to the weight of the liquid it displaces.
Upthrust: The upward force exerted by a liquid on an immersed object.
Formula: $Upthrust = \rho g V$ (where $\rho$ is density of liquid, $V$ is volume of object).
A floating object displaces a weight of fluid equal to its own weight.
If $Weight > Upthrust$, object sinks.
If $Weight = Upthrust$, object floats.
Elasticity: Property of a body to restore its original size and shape after deforming force is removed.
Stress: Force acting on unit area ($Stress = F/A$). Unit: $Nm^{-2}$.
Strain: Ratio of change in dimension to original dimension (Change in length / Original length). It has no unit.
Statement: Within elastic limit, the strain produced in a body is directly proportional to the stress applied to it.
$Stress \propto Strain$
$F = kx$ (for springs).
Definition: The ratio of tensile stress to tensile strain.
Formula: $Y = \frac{Stress}{Strain} = \frac{F/A}{\Delta L / L_o} = \frac{F \times L_o}{A \times \Delta L}$
Unit: $Nm^{-2}$.