Physics IX Notes Chapter 7 Properties of Matter

kinetic molecules model of matter:- according to this theory matter consists of small particles called modules. Modules are made of a small particle called atoms. These molecules are always in a state of motion. The motion may be linear, vibrational or rotational and this motion is increased with an increase in temperature, there is a force of attraction between the molecules which depend upon the distance between them. Their kinetic energy is due to their motion and potential energy is due to the force of attraction between them.

State of matter explained below on the bases of molecular theory?
Solids:-
solids have a definite shape and a definite volume.
In solids, molecules cannot transfer from one place to another.
Their molecules perform the vibratory motion.
Their molecules are increased with an increase in temperature.

Liquids:-
I. Liquids have a definite volume but no definite pe.
II. Molecules in liquids are loosely bonded to each other.
III. In liquids, molecules can transfer from one place to another.
IV.Force of attraction b/w molecules is weaker than solids.
V. Their K.E increases with an increase in temperature.

Gases:-
they have neither definite shape nor volume.
Their molecules are at a large distance from one another.
Their molecules can move freely and perform the random motion.
Force of attraction b/w molecules in temperature.
Plasma:- this is the 4thstate matter which is found in an ionized state; it is called plasma that exists in the sun.

Density:- The mass of unit volume is called density it is denoted by (Rho).
Explanation:-if mass of a body is “m” and volume of that body is “v” then we can write its mathematical form as;
From its mathematical form, it is clear that density is the intermolecular force b/w then.
Density is a vector quantity and its unit is kg/m3.

Pressure:- force per unit area is called pressure if we have a unit area “A” at which force “F” is acting then the press “P” is given by/
Pressure = force/area => p = f/A
Its unit is Pascal.

The force excreted by the thick layer of air surrounds earth is called atmospheric pressure
This is a layer of air around us which is called the atmosphere. We live in the ocean of air which exerts a force upon our body and it is equal to 100,000 Pascal which is called one atmospheric pressure.

A device which is used for measurement of atmospheric pressure is called barometer consists of a glass filled with mercury one end of the glass is sealed and the other is dipped in mercury when atmospheric pressure presses the mercury toward the mercury rises up in glass tube the glass is graduated with different values the height of mercury in the glass shows the value of atmospheric the pressure at sea level the mercury can rise up to 16cm at 00c and it is known as the standard of atmospheric pressure.

Some applications of atmospheric pressure are given below.

Sucking throws straw­:- when we suck any liquid through a straw the volume of lungs increases and the air pressure decreases. As a result of the atmospheric rise in straw.

Surfing:– when we draw any liquid with the help of syringe the pressure inside the syringe decreases while the pressure a surface of liquid increases which forces the liquid ongoing into the syringe.
while the pressure on the surface of liquid increases which forces the liquid ongoing into the syringe.

If we keep the barometer at the same high above the sea level it will show the changes of the day by day pressure. These pressure changes are shown on a weather map. These lines which link all places at the same atmospheric pressure are called I so bar. The unit which is used for weather map is called mill bar ( m bar)

100m bar = 1 bar => 1bar = 100kpa

The atmospheric pressure usually changes from 1040 bar to as low as 950 bar. The wind moves from high-pressure regions to low-pressure regions. The winds of low-pressure areas move anticlockwise while the wind of high-pressure areas move clockwise in the northern hemisphere. The strength of the wind is determined by the pressure gradient.

Pascal’s law:-This law states that pressure exerted at any point and liquids in any container is distributed equally in all directions.

Explanation:- consider a container having four openings A, B, C and D as shown In figure. There are moveable pistons in every opening.
Now if we use this container with water or any other liquid. Then we apply some force on anyone piston of them. Suppose we apply force on “A” as soon as we apply force on piston “A” at the same time the other three pistons will also start moving outwards. This experiment shows that pressure exerted on any liquid in any container is distributed equally in all directions.