Law of conservation of momentum states that : For two or more bodies in an isolated system acting upon each other, their total momentum remains constant unless an external force is applied. Therefore, momentum can neither be created nor destroyed.

Newton’s third law states that for a force applied by an object A on object B, object B exerts back an equal force in magnitude, but opposite in direction. This idea was used by Newton to derive the law of conservation of momentum.

Consider two colliding particles A and B whose masses are m₁ and m₂ with initial and final velocities as u₁ and v₁ of A and u₂ and v₂ of B. The time of contact between two particles is given as t.

A=m₁(v₁−u₁) (change in momentum of particle A)

B=m₂(v₂−u₂) (change in momentum of particle B)

F_BA=−F_AB (from third law of motion)

F_BA=m₂∗a₂=m₂(v₂−u₂)/t

F_AB=m₁∗a₁=m₁(v₁−u₁)/t

m₂(v₂−u₂)/t=−m₁(v₁−u₁)/t

In physics, spacetime is any mathematical model which fuses the three dimensions of space and the one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive differently where and when events occur.

The flying of aeroplane is due to application of bernaullis theorem

the wings of the aeroplane are made in such a way that the pressure of the air above the wings decreases and due to which the plane lifts up

9 Science notes Chapter 6 Tissues

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Tissue

A group of cells that are specialized to perform a particular function forms a tissue.

Tissues are mainly classified into two types:
1. Plant Tissues 2. Animal Tissues

1. Plant tissues

• Plants do not move, i.e., they are stationary.
• Most of the tissues they have are supportive, which provides them with structural strength.
• Most of these tissues are dead, as they can provide better mechanical strength than the live ones, and need less maintenance.
• Some of the plant tissues keep on dividing throughout the plant life. These tissues are localised in certain regions.

Types of Plant Tissues:

Based on the dividing capacity of the tissues, various plant tissues can be classified as growing or meristematic tissue and permanent tissue which have further sub-divisions as explained below:

Tissues
Group of cells having a common origin and similar function are termed as tissues.
A. Plant tissues: On the basis of the dividing capacity, plant tissues are of two types:

1. Meristematic tissues
2. Permanent tissues

1. Meristematic tissues: Consist of actively-dividing cells. Meristematic tissues are of three types:

• Apical meristem: Present at the growing tips of stems and roots. Important function: To increase the length of stems and roots.
• Intercalary meristem: Present at the base of leaves or internodes. Important function: For the longitudinal growth of plants.
• Lateral meristem: Present on the lateral sides of the stems and roots. Important function: To increase the thickness of stems and roots.

2. Permanent tissues: Formed from meristematic tissues, the cells in the tissue loose the ability to divider Permanent tissues are divided into two categories:

• Simple permanent tissue: Consist of only one type of cells.
  Types of simple permanent tissues:
   
• • Parenchyma: Composed of unspecialised living cells with relatively thin cell walls, intercellular space, present in soft parts of the plant. Their main function is storage.
  • Collenchyma: Composed of living and elongated cells with cell walls irregularly thickened at the comers. No intercellular space. It provides mechanical support and elasticity to plant. It helps in bending of leaves and stems.
  • Sclerenchyma: Composed of long, narrow, and thick-walled cells. This tissue is made up of dead cells and there are no intercellular spaces. Sclerenchyma cells are dead, present in seeds, nuts, the husk of a coconut, fibres of jute etc.
• Complex permanent tissue: Made up of more than one type of cells (Conducting tissues.)
  Types of complex permanent tissues:

   

  • Xylem: Conducts water and minerals from the roots to the different parts of the plant.
    Composed of four different types of cells—tracheids, vessels, xylem parenchyma and xylem fibres.
  • Phloem: Conducts food material from the leaves to the different parts of the plant.
    Composed of four different types of cells—sieve tubes, companion cells, phloem parenchyma and phloem fibres.
    Protective tissue: It is made of a single layer of cells. E.g., epidermis. The epidermis of the leaf bears stomata.

h=1 m.  h'=9 m.

t=0.1 s. t'=1 s.

Now force exerted in first case be F and in second case be F'.

Let the mass of man be m.

F= ma = m(change in velocity/change in time) = m(v-0)/t = m(sqrt(2gh))/t 

F'=m(sqrt(2gh'))/t'

=> F/F'= sqrt(h/h')*t'/t

=>F/F'= sqrt(1/9) *1/0.1 = 10/3

Hence , F'=(3/10)F.

d

• A German scientist, E.Goldstein modified the discharge tube and passed an electric current through it.
• He found that positively charged rays were emitted from the anode in the discharge tube. These rays were called 'Canal Rays'.

• When an electric field was applied, these rays deflected towards the negatively charged plate. Thus, Goldstein concluded that an atom contains positively charged particles along with the electrons.
• These positively charged particles were named as 'protons' by a British scientist, Ernest Rutherford.
• Canal rays were also called anode rays since they emitted from anode (electrode connected to positive terminal of high voltage source) in the gas discharge experiments using perforated cathode.

When the ball is dropped from height h, speed v of the ball when it reaches ground is calculated using the equation, " v² = 2×g×h "

hence speed v = 

Time taken t to reach the ground is obtained using the equation " h = (1/2)×g×t² "

hence time taken t to reach ground  = 

Hepatitis is an inflammatory condition of the liver. It disturbs various metabolic processes such as bile production, excretion, fat and protein metabolism, activation of enzymes and synthesis of proteins.

A cell is defined as the smallest, basic unit of life that is responsible for all of life’s processes.

Cells are the structural, functional, and biological units of all living beings. A cell can replicate itself independently. Hence, they are known as the building blocks of life. 

F= GMm​/R²

 If one mass say, m is doubled, then force is

F′= 2GMm​/ R² ==2F the force gets doubled.

“Conduction is the transfer of heat from the hotter part of the material to its colder part without the actual movement of the particles. What I want to say here is that in the process of conduction there is no net movement of the particles of the body. Heat passes through solids by conduction only.

1. Molecular compounds are pure substances formed when atoms are linked together by sharing of electrons while ionic compounds are formed due to the transfer of electrons.
2. Molecular compounds are made due to covalent bonding while ionic compounds are made due to ionic bonding.
3. Molecular compounds are formed between two non-metals while ionic compounds are formed between metals and non-metals.
4. Molecular compounds are poor electrical conductors while ionic compounds are good conductors.
5. Molecular compounds can be in any physical state ‘“ solid, liquid, or gas. Ionic compounds are always solid and crystalline in appearance.
6. There are a lot of molecular compounds than ionic compounds.

initial velocity, u = 6 m/s and final velocity, v= -4.4 m/s

time = 0.04s

thus acceleration = (v-u)/t

a =(- 4.4 - 6)/ 0.04  = -10.4/ 0.04  = -260 m/s² 

Note: v is taken as negative because it's in opposite direction as that of initial velocity. 

Photosynthesis is a process plants use to convert the light energy from the sun into chemical energy that they can use

• The chemical energy is a molecule of sugar called glucose

• Plants and animals use this for food.

Lignin is deposited in the cell wall of sclerenchyma.

(a) In the upper layers of the atmosphere, a layer of ozone is formed, which gets depleted due to chloro fluoro carbons and creates a hole called ozone hole.

(b) Ozone hole is found above Antartica, over the North pole.

(c) UV radiation will reach the earth and cause diseases like - cancer, reduce immunity and reduce crop yield.

The ozone layer present in the stratosphere acts as a protective shield. It saves the earth from the harmful ultraviolet rays of the sun. The compounds containing CFCs (chlorofluorocarbons) are mainly responsible for ozone layer depletion as these compounds react with ozone in the presence of ultraviolet rays to form oxygen molecule and thus, destroying ozone.
 

The harmful effects of UV radiations are as mentioned below
1. causes skin cancer
2. cause sun burn
3. damage immune system
4. damage eyes
5. ages skin
6. weakens plastics
 

• Ozone is a molecule of oxygen with three atoms of oxygen, O₃.
• It covers the Earth’s atmosphere and is present in the stratosphere. It does not allow the harmful ultra-violet radiations coming from the sun to reach our Earth surface.
• These ultra-violet radiations cause ionising effect, can cause cancer and genetic disorder in any life-forms.
• The ozone is getting depleted at the south pole near Antartica. The ozone depletion is due to the halogens like CFC (chlorofluorocarbon) released in the air.
• Chlorine and fluorine reacts with the ozone and splits it, thereby leading to formation of a big hole called ozone hole.
• Thus, we need to protect the ozone layer from getting depleted by reducing the consumption of fossil-fuels and other factors which leads to the depletion of ozone layer.

The thinning of ozone layer allows more ultra violet (UV) radiations to pass through it which then strike the earth. These cause following harmful effects on man, animals and plants:
(i) Skin cancer.
(ii) Damage to eyes, also increase incidence of cataract disease in eyes.
(iii) Damage to immune system.
(iv) Increased embryonic mortality in animals and humans.
(v) In plants too, there will be increased death rate of seedlings, increased incidence of harmful mutations and reduction in yields.

Oxygen molecule splits into atomic oxygen (O) at higher levels of an atmosphere because of higher energy of UV radiations.

So, O2​⟶O+O

O2​+O⟶O3​ (Ozone)

Damage to the ozone layer is a cause of concern to us as it forms a layer in the atmosphere which protects us from the harmful UV radiation.

Damage to ozone layer can cause penetration of UV rays in the earth surface which damages human organs, plants, etc.