 Chapter 7 Properties of Matter Physics Class 9th Notes »

# Chapter 7 Properties of Matter Physics Class 9th Notes

Chapter 7 Properties of Matter Physics Class 9th Notes

## Chapter 7 Properties of Matter Physics Class 9th Notes

Q.1 explains the kinetic molecular model of matter?

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

Q.2 explains the states of matter on the bases of molecular model of matter?

Ans. State of matter explained below on the bases of molecular theory?
1. Solids:-
solids have defined shape and definite volume.
In solids molecules cannot transfer from one place to another.
Their molecules perform vibratory motion.
Their molecules are increased with increase in temperature.
2. Liquids:-
Liquids have definite volume but no definite pe.
Molecules in liquids are loosely bided to each other.
In liquids molecules can transfer from one place to another.
Force of attraction b/w molecules is weaker then solids.
Their K.E increase with increase in temperature.
3. Gases:-
they have neither definite shape nor volume.
Their molecules are at large distance from one another.
Their molecules can move freely and perform random motion.
Force of attraction b/w molecules in temperature.
4. Plasma:- this is the 4th state matter which is found in ionized state it is called plasma exist in sun.

Q.3 Define and explain “Density”?

Ans. Density:- the mass f 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 the inter molecular force b/w then.

Density is a vector quantity and its unit is kg/m3.

Q.4 Defines pressure?

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

It’s unit is Pascal.

Q.5 Define and explain atmospheric pressure?

Ans. 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 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 presser.

Q. 6 write a note on barometer?

Ans. Barometer :- A devise which is used for measurement of atmospheric pressure is called barometer consists of a glass filled with mercury one end of 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 glass shows the value of atmospheric pressure at sea level the mercury can rise up to 16cm at 00c and it is known as standard of atmospheric pressure.

Q..7 write application of atmospheric pressure in our daily life?

Ans. Some applications of atmospheric pressure are given below.

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

Suring:– when we draw any liquid with the help of syring the pressure inside the syring decreases while the pressure an surface of liquid increases which forces the liquid on going into syring.

while the pressure an surface of liquid increases which forces the liquid on going into syring.

Q.8 explains that how weather changes with atmospheric pressure.

Ans. If we keep barometer at same high above the see level if will show the changes of day by day pressure. These pressure changes are shown a weather map. These lines which loins 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 mbar to as low as 950 mbar. The wind moves from high pressure regions to low pressure regions. The winds of low pressure areas move anti-clock wise while the wind of high pressure areas move clock-wise in northern hemisphere. The strength of wind is determined by the pressure gradient.

Q.9 state and explain Pascal’s law?

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

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 this container with water or any other liquid. Then we apply some force on any one 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 a pressure exerted on any liquid in any container is distributed equally in all direction.

Q.10 write some practical applications of Pascal ‘slaw?

Ans. Hydraulic lift:-     a devise which is use for lifting heavy leads, and works with the help of liquid pressure is called hydraulic lift. If works on Pascal’s principles diameter which are connected with each other by a tube. These cylinders are filled with some liquid and their top ends filled with piston.

When some pressure is exenterated on piston “A” in downward direction. Then this pressure is transmitted to piston “B” in upward direction and by this way it lift. Lead. If “F1” is the force applied on piston “A” and “A1” is its area then pressure on it is given by P1=  F2 /A1……………….(i)

Similarly pressure on pis to B is                                             P2  F2 /A2…………………(ii)

But according to Pascal’s law we have ;

P1 = P2 => f1/A1 = F2 /A2 = => F2 = F1A2/A1

By this equation we can find force exerted on piston “B”

Hydraulic brake system:- such brake system in which oil is used for stopping wheel is called hydraulic brake  system.

Explanation:– it consists of five cylinders. One of then is bigger cylinder called master cylinder. The other four small cylinders are connected with master cylinder by a tube. The other end of smaller cylinders is connected with wheel.

When a pressure is applied on oil transmits this pressure to small cylinders through liquid. Which finally stops the wheel?

Q.11 explains pressure in liquids with its mathematical form?

Pressure in liquids:-liquids have weight and the ability of flowing because of which pressure of liquids can be easily explained. Liquids have pressure which they exerts in all direction equally. The pressure of liquids depends upon their weight, density and hight.

Explanation:- let suppose we have a container filled with a liquid. If “W” is they weight of liquid “A” is area

of bottom of container and “h” is hight of container. Which is filled with water as shown in. then the pressure in given by?

Pressure = force /Area => force

• Pressure = weight /Area           because force = Wight.
• P = w/A =>  p= mg/A ..,…..(i) [w = mg]

Now as we know that    L = m/v            => m = Lv

Putting value of  ineq (i) , we get;

P = lvg/A…………….(ii)

But we also know that   v = area x hight => v = Ah

So, eq (ii) becomes; p = LAhg/ AP= Lhg

this equation shows us the pressure exerted by liquid.

Q.12 Explain the up thrust force in l liquid?

Ans. Up thrust force:- the force exerted by a liquid in opposite direction against the weight of the body is called up thrust force.

Explanation:-when we immerse a cork in water it floats on the surface of water because the up thrust force on cork is greater then its weight.

Similarly when a balloon is filled with helium gas and then released, it will move in upward direction because air is dense than helium gas. And up thrust force on balloon is greater than its weight and as a result it moves in upward direction.

Q.13 state and explain Archimedes principle?

Archimedes principle:- This principle states that when a body is wholly or partially immersed in a fluid, then on up thrust force (Fb) acts on body which is equal to the weight of displaced water. (OR) simply we can say that;

Beyond force or up thrust acting on an object = weight of liquids displaced by it.

Explanation:-when a body is body is immersed in liquids then two forces act on body its weight “w” acting in down ward direction. The up thrust force “Fb” acting in upward direction.

Which is equal to the weight of displaced water now if Fb<“W” then the weight exceeds up thrust force and body will sink down. If Fb= w then weight and up thrust balances each other and body floats in liquid. So, the above discussion can also be stated as;

Law of floatation:- A floating body displaces its own weight of the fluid in which it floats”

Explanation:-the sinking of objects can also be explained in term of their densities. Suppose we have a body of mass “m” it’s volume is “V” and density is “f”  let volume of liquid is “v” and density is “f” in which it is immersed then according to law of flotation we have;

Weight of the object = weight of the fluid displaced.

Mg =  mg (w = mg )

• Fvg = fvg (m = fv)
• Fv = fv => f/f = v/v
• Now I density of the object is less than the density of fluid ( f < f ) then the object well float in fluid and will be immured totally

Q.14 what is effect of buoyant force on floating bodies?

Ans. Effect of buoyant force on bodies ­:- when a body is immured in liquid, two forces act on body its weight “w” in downward direction and up thrust force (Fb)m in upward direction; now

1. If weight is greater than up thrust forces W>Fb then body will sink.
2. If weight of body is less than up thrust force ie W <fb  then body will float on the surface of water.
3. If weight and up thrust force are equal ie W = fb then the body will either sink or float buy it will remain floating water surface.

Q. 15 define and explain elasticity? Also define be elastic limit?

Ans. Elasticity:-the property of a substance due to which it can regain its original shape after the removal of applied force is called elasticity.

Explanation:-when we compress a spring it changes its shape because of force but when we remove the applied force from body. It comes back to its original shape this property of bodies is known as elastic and the body having this characteristic is called elastic body.

Not only metals and other bodies are elastic but our body muscles are also elastic most of the actions of our body are possible due to expansion and contraction of muscles.

Elastic limit :-with in which a body can regain its original shape is called elastic limit

If the deforming force crosses the elastic limit then under such conditions permanent changes occurs in shapes of body and the body is unable to regain its original shape.

Q. 16 define and explain hook’s law?

Ans. Hook’s law:-this law states that with in elastic limit the compression or extension is directly proportional to the applied force.

Explanation:-let “F” is the force applied on a body which produces extension or compression in a body then according to Hook’s law;

F = x

• F = k x ………………….(i)

Equation (1) shows mathematical form of Hook’s law where “k” is constant of proportionality

Now if F = and x = E where “ ” is stress and “E” is strain then eq (1) becomes;

• = k E ………..(2)

So, we can also define Hooks law that with in elastic limit stress is directly proportional to produced strain.

Q.17defines (i) stress (ii) linear stress (ii) strain (iv) linear strain?

i. stress :- the force applied on unit area of on object which changes its shape is called stress. It is denoted by “ ” mathematically is given as;

Stress = force/ Area        =>  = F A

it’s unit is N/m2

ii.  linear stress:-the force applied on a body along it length is called linear stress”

1. strain:-the extension or changes per unit length or area is called strain it is denote by “E”.
2. linear strain:-  the changes occurred in length of a body due to linear stress is called linear strain

E  =

Where “  is change in original long “L”

Q.18 Define young’s modulus? Also give its unit?

Ans. young’s Modulus:- The ratio of linear stress and linear strain is called young’s modules it is represented by “Y” and given by;

Young Modulus =

• Y =  = F/A

And also

So, putting these in equation (1) we get.

Y =                                  => y =

It’s unit is N/m2

## Coneptual Question

Q.1 why is the cutting edge of the knife made very Sharpe?

Ans. we know that pressure is inversely proportional to area that’s why cutting edge of the knife is made very sharp by doing so, the area becomes smaller and the pressure becomes greater. This we can cut things easily by knife.

Q.3 why we cannot use water instead of mercury in barometer?

Ans. we cannot use way we instead of mercury because;
Water density is less than mercury.
Water is not sensitive as mercury to change by pressure.
Expansion of mercury is uniform.
Water is not easily visible to record data.
Freezing point of water is higher than that of mercury

Q.5 why miners in mines face breathing problems/

Ans. the miners in mines face breathing problems due to lack of ventilation. Deficiency of oxygen and excess of carbon dioxide gas.

Q.6 what is the basic principle hydraulic press?

Ans. The basic principle of hydraulic press is Pascal’s principle that is liquid exerts presser in all direction equally.

Q.7 why water tanks are constructed at high level our increases?

Ans. We know that water pressure increases with height therefore easy flow of water and high pressure in a pipe system water tanks are constructed at the highest levels in our houses.

Q.8 why a small needle sinks in water but huge ships travels easily in water without sinking?

Ans. A small needle sinks in water because the weight of needle is greater that weight of water displaced by it. While a huge ship does not sink but flow on water surface because the weight of ship is less than the weight of water displaced by it.

Q.9 which material is more elastic steel or rubber, why?

Ans. Steel is more elastic than rubber because for a given stress the strain produced in a steel is much smaller than rubber.

Q.10 walnuts can be broken in the hands by squeezing two together but not one why?

Ans. Walnuts can be broken in the hands by squeezing two together but not one, because the contact area decreases significantly due to which the stress or pressure increases and as a result the walnuts can be broken easily.

Q.11 explains how how and why camels have adapted to allow them to walk more easily in desert condition?

Ans. As we know that camels have feet with comparatively large surface area, therefore they exerts little pressure and can walk easily in desert.