3. Answer of conceptual level question 4.1 :
Here materials are divided into 3 main groups
according to the properties.
They are solid , liquid and gas
Solid : Aluminium , Gold ,Coir ,Twine, Rubber
Liquid : Water , Kerosene, Coconut oil
Gas : Oxygen, Air , Carbon dioxide
4. 1 .What is meant by elasticity?
Ans : The property of solids to retain its original size or shape
after the removal of deforming force is called elasticity.
Or
The ability of some solid material to generate internal force
against the deformation force applied externally.
2. What is meant by elastic materials ? Give examples
Ans : The materials with the elastic property are called elastic
materials.
Examples : Quartz, Phosphor bronze (an alloy of phosphor and
bronze), steel, glass, ivory, are perfectly elastic bodies
5. 3 .What is meant by plasticity?
Ans: Some materials remain in the deformed state
without showing any tendency to regain its original size
or shape when the applied force is removed. The
property of a material to undergo permanent
deformation under applied force is called plasticity.
4) What is meant by plastic materials ? Give exapmles
Ans: Materials showing plastic behaviour are called
plastic materials. Examples : Clay, mud, plaster of Paris,
etc. are examples of plastic materials
6. 5) What is meant by deforming force?
Ans:The force when applied on a body if that forcce is able to
changes its shape,then that force is called deforming force.
6) What happens When We strech a rubberband?
Ans: If we keep the rubber band in a stretched state for some
time, we feel some pain in our hands. That is there is a
counterforce against the applied force developed internally in our
rubber material to retain its original dimension.
7) What is meant by restoring force?
Ans:The internal reaction force developed inside an elastic
material to resist any change in its size or shape is called restoring
force.
7. 8)What is meant by Stress? Write its formula and unit of stress
8. 9) What is meant by Strain? Write formula of strain
10) Why Strain has no unit,explain
Ans:
10. 12)Explain Hooke’s law
Ans: Hooke’s Law states that the stress is proportional to the
strain, within the elastic limit.
𝑠𝑡𝑟𝑒𝑠𝑠 ∝ 𝑠𝑡𝑟𝑎𝑖𝑛
The constant of proportionality depends on the material being deformed and on the
nature of the deformation and it is called as modulus of elasticity or elastic modulus.
Since strain is a pure number, the unit of elastic modulus is the same as that of stress is
11. 13) What is meant by modulus of elasticity or elastic modulus
write unit of modulus of elasticity or elastic modulus.
Ans: Hooke’s Law states that the stress is proportional to the strain, within the elastic
limit.
𝑠𝑡𝑟𝑒𝑠𝑠 ∝ 𝑠𝑡𝑟𝑎𝑖𝑛
The constant of proportionality depends on the material being deformed and on the
nature of the deformation and it is called as modulus of elasticity or elastic modulus.
Since strain is a pure number, the unit of elastic modulus is the same as that of stress is
12. 14)What is meant by Young’s Modulus: Elasticity of
Length,explain. Write its formula and unit
Ans:
18. 14)What is meant by,explain Rigidity Modulus: Elasticity of
Shape ,Write its formula and unit
Ans:
Another type of deformation occurs when an object is subjected to a
deforming force parallel to one of its faces while the opposite face is
held fixed by another force.
Consider a book with a considerable thickness (A dictionary or
something), place it on a table and
gently push sidewise with your palm
which is placed over the book.
19. The rectangular or square box type book now looks like a
parallelogram box.
The stress in this case is called shear stress.
If the object is originally a rectangular block, shear stress
results in a shape whose cross-section is a parallelogram.
That is, we are deforming the shape of the object without
changing its volume by applying a parallel deforming force to
one of the faces of the object. This is called shearing
21. 15 )What is meant by shear stress
Ans:
Another type of deformation occurs when an object is subjected to a deforming
force parallel to one of its faces while the opposite face is held fixed by another
force.
Consider a book with a considerable thickness (A dictionary or something), place it
on a table and gently push sidewise with your palm which is placed over the book.
The rectangular or square box type book now looks like a parallelogram box.
The stress in this case is called shear stress.
22. 16) What is meant by shearing?
Ans: Another type of deformation occurs when an object is subjected to a deforming force
parallel to one of its faces while the opposite face is held fixed by another force.
Consider a book with a considerable thickness (A dictionary or something), place it on a
table and gently push sidewise with your palm which is placed over the book.
The rectangular or square box type book now looks like a parallelogram box.
If the object is originally a rectangular block, shear stress results in a shape whose cross-
section is a parallelogram. That is, we are deforming the shape of the object without
changing its volume by applying a parallel deforming force to one of the faces of the
object. This is called shearing
23. 17)What is meant by Bulk Modulus: Volume Elasticity
,explain Write its formula and unit
Ans:
24.
25. 17) What is meant by compressibility,explain Write its formula and unit
Ans: The reciprocal of the bulk modulus is called the compressibility
and is denoted by 𝑘
27. Conceptual Learning 4.3
Answers:
1. Water and mercury are liquids and they have no definite size or shape. we can only
calculate Bulk modulus for water and mercury
Young’s modulus and Rigidity modulus can be calculated for solids only.
2. Water and mercury are liquids
3. water and mercury can have volume change on application of deforming force.So we
can calculate bulk modulus for water and mercury
33. 18)What is meant by PRESSURE. Write its formula and unit
Ans:
Pressure (P) is defined as the perpendicular or normal force acting per
unit area of a substance.
19) Define the pressure one Pascal
Ans: One pascal is the pressure exerted by a force of 1 N on an area of 1
20) What are other units of Pressure
Ans: bar is another unit of pressure
1
1
34. 19) what happens to a man if an elephant steps on his chest. But in the circus, the
same act is performed with the help of a wooden plank.How is this possible?
Ans:
We know what happens to a man if an elephant steps on his chest.
The impact of force ill be more if elephant steps on the chest of man.Man may die,
The smaller the area on which the force acts, the greater is the Impact.There ill be more
pressure
But in the circus, the same act is performed with the help of a wooden plank. Here the area
is more, then the force acting will have less impact.There will be less pressure
Since
As area increases,the value of pressure decreases
35. Ans:
In the question weight is given.Here weight is actually force
Area of cube A = side x side
Cross sectional area of cylinder is
39. Ans:
4)
Given ,
Force =25N
Radius = 1m
Cross sectional Area of cylinder
A = 3.14 x (1x1)=3.14
P = 25/3.14=7.96
Therefore Pressure will be more for cubic box of weight 25 N and 1.5 m sides
40. 21) What is meant by Pressure inside a Fluid or (Hydrostatic pressure)
Ans:The force exerted by a static fluid on an object is always
perpendicular to the surfaces of the object and this perpendicular
force per unit area is called hydrostatic pressure.
Hydrostatic pressure is the pressure that is exerted by a fluid
at equilibrium at a given point within the fluid, due to the force of
gravity or weight of the fluid.
41. 22) Why Pressure is not a vector quantity ?
Ans: Pressure is not a vector quantity.Pressure is scalar quantity. It acts in any
direction with the same magnitude. That is, it has no directional property. It is
true that force acting on the surface is a vector quantity, but the expression for
pressure involves only the magnitude of force. And the value for pressure thus
obtained is independent of the orientation of the surface area
23) Define Pascal’s Law
Ans:Pressure is the force per unit area acting normally to a surface element
within a fluid. Due to the high mobility of the molecules of the fluid, the force
acting at one position propagates immediately and isotropically with the same
magnitude through the entire volume of the fluid.Within a fluid at rest, the
normal force exerted on a small surface has the same magnitude everywhere
and is independent of the orientation of the surface. This is called Pascal's law.
The Pascal’s law is behind hydraulic machines like a crane, break, lift, etc.
42. 24) What is atmospheric pressure?Name the instrument used to measure atmospheric pressure
Ans: The atmospheric pressure at any point is equal to the weight of a column of air of
unit cross-sectional area extending from that point to the top of the atmosphere
Atmospheric pressure can be measured with a mercury barometer in which pressure is
measured in terms of the height of the mercury (Hg) column
At sea level, atmospheric pressure corresponds to 76 cm of Hg which is
equivalent to
25) Define I atmospheric pressure or 1 atm
Ans: One atmosphere (atm) is a standard unit of pressure equal to the mean atmospheric
pressure at sea level.
26) Why do mountaineers get bleed through their nose or ear at high altitudes?
Ans:The atmospheric pressure decreases with an increase in altitude. The higher we climb up a
mountain, the lesser will be the air above us and therefore, the lower will be the atmospheric
pressure become. Mountaineers get bleed through their nose or ear due to this pressure
difference.
43. 27) What happens to atmospheric pressure When go to higher altitudes
and What happens if We go deep within water or ocean?
Ans : Atmospheric pressure decreases with increase in height.As we move
to higher altitudes the atmospheric pressure decreases
The pressure inside the water increases with depth.As we go deep down
within the ocean pressure increases
28) What is Absolute pressure and Gauge pressure ?
Ans:
The P absolute pressure at that point is the sum of atmospheric pressure
and
The excess of pressure ,at depth, h is called a gauge pressure at
that point.
Gauge pressure at a point is the pressure measured relative to the
atmospheric pressure
