When an object moves along a straight line with uniform acceleration, acceleration during motion and the distance covered by it in a certain time interval by a set of equations known as the equations of motion. Three equations of motion:

i. v  = u + at

ii. s  = ut + ½ at²

iii. 2as  = v² – u²

where u is the initial velocity of the object which moves with uniform acceleration a for time t, v is the final velocity, and s is the distance travelled by the object in time t.

Chordates are animals characterized by the presence of notochord at some stage during their development. Members possess a hollow nerve cord and pharyngeal gill slits. The other general characteristic features of Chordates are as follows:

• They are bilaterally symmetrical, triploblastic, and coelomate with the organ-system level of organization.
• They hold a post-**** tail
• The body includes a closed circulatory system.
• In some members of Phylum Chordata, the notochord is present only in the larval tail, and in some, it is present throughout their life from head to tail region.
• Chordates have many sub-divisions and Protochordates are one of the earliest to evolve.

Examples of this phylum include Ascidia, Salpa, Doliolum, Amphioxus or Lancelet.

Characteristics of Annelida:

(i) Body triploblastic, bilaterally symmetrical, soft, elongated, vermiform and cylindrical or dorsoventrally flattened.

(ii) Exoskeleton absent; body is covered by a thin cuticle.

(iii) Alimentary canal is tube-like, complete and extends straight from mouth to ****.

(iv) Reproduction is by sexual means. Sexes may be united (hermaphroditic) or separate.

(v) True coelomate animals with closed blood vascular system. Coelom allows true organs to be packaged in the body structure.

(vi) They live in a variety of habitats. Mostly aquatic, marine or fresh water. Some are terrestrial, burrowing in tubes, some free-living forms.

Example: Nereis (sand worm) and Hirudinaria (leech).

The atmosphere is divided into five layers beginning from the surface of the Earth. These are:

Troposphere

• It is the most important layer of the atmosphere and it extends up to 13km from the surface of the Earth.
• Oxygen, that we breathe exists in this layer of the Earth.
• The temperature decreases in this layer with the increase in height.
• All weather phenomena like rainfall, hail and fog occur in this layer as the clouds are formed in this layer.
• The upper limit of the troposphere is known as the tropopause. Temperature may be as low as -580C
  at this level.

Stratosphere

• This layer of atmosphere lies above the troposphere and it extends up to a height of 50km.
• Airplanes fly in this layer, as this layer is free from clouds and other weather phenomena. This layer is also free from water vapour and dust particles.
• Stratosphere contains a layer of ozone gas which protects us from the harmful ultra violet rays of the Sun.
• In the higher levels of the stratosphere, the temperature increases with height due to the absorption of UV rays by the ozone in the layer.
• The upper part of the stratosphere is known as stratopause.

 Mesosphere

• This is the third layer of the atmosphere and it lies above the stratosphere up to a height of 80kms.
• It is in this layer that meteorites burn when they enter into the atmosphere from space.
• The upper layer of the mesosphere is known as the mesopause.

Thermosphere or Ionosphere

• This layer extends from 80-400km.
• Temperature increases drastically in this layer and can go up to 1,4800C.This is because the molecules in this layer absorb the Sun’s UV rays.
• Thermosphere helps in the transmission of radio waves as the latter is reflected back to the Earth by this layer.

 Exosphere

•  It is the uppermost layer of the Earth.
• It has very thin layer of air.
• Light gases like helium and hydrogen float into space from this layer due to the lack of gravity.
• This layer extends from 480 km to 960 km above the Earth.
• Temperature increases with height in this layer. The temperature may well go beyond 55000C

We know that kWh is a commercial unit
1kWh = 1kW × 1h
1000 W × 3600 seconds
1 watt × second = 1 joule
1kWh = 3600000 J

Floatation is the act, process, or state of floating.

1. If the buoyant force exerted by the liquid is less than the weight of the object, the object will sink in the liquid.
2. If the buoyant force exerted by the liquid is equal to the weight of the object, the object will float in the liquid.
3. If the buoyant force exerted by the liquid is more than the weight of the object, the object will rise in the liquid and then float.

So, we can conclude that an object will float in a liquid if the upward buoyant force it receives from the liquid is great enough to overcome the downward force of its weight.

The law states that mass can neither be created nor destroyed in a chemical reaction i.e. Total masses of reactants is equal to the sum of masses of products and the masses of unreacted reactants. For instance, the reaction of carbon with oxygen to produce carbon-dioxide involves conservation of mass in the following way.

C (12g) + O₂ (32g) = CO₂ (44g)

Here we used 12 g of carbon and 32 g of oxygen. After reaction the amount of carbon –dioxide produced will be 44g i.e. the sum total of the amount of  carbon and oxygen used.

Propagation of Sound

• Sound waves move from the point of generation to the listener through the medium.
• When an object vibrates and produces sound, the particles of the medium at the point of generation begin to vibrate.
• This particle passes on the vibration to its adjacent/neighboring particle. The first particle comes back to its equilibrium position of rest. Then the second particles passes its vibration to the neighboring third particle and then again comes back to its position of rest. This process continues until the vibration reaches the listener and he is able to hear the sound.
• As we see, the actual particles of the medium don't travel from the point of generation to listener. It is only the vibration that travels through the medium. This is called Wave motion.
• A wave is a disturbance that moves through a medium when the particles of the medium set neighboring particles into motion. Since sound waves are characterized by the motion of particles in the medium, they are Mechanical Waves.

The movement of water molecules through a selectively permeable membrane is called osmosis. It is affected by the amount of substance dissolved in water. Thus, osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. If we put an animal cell or a plant cell into a solution of sugar or salt in water then three things could happen:

(i) When eukaryotic cells are placed in hypotonic solutions, the water molecules will enter into the cell and the cell will swell up.

(ii) If eukaryotic cells are placed in hypertonic solutions, the water molecules will come out of the cell and the cell with shrink.

(iii) If the eukaryotic cell is placed in isotonic solution, the amount of water molecule will remain the same; it will neither move out or will go inside. The cell will remain same sized.

The buoyant force depends directly upon:

• Volume of the fluid displaced.
• Density of the fluid in which the body is immersed.
• Acceleration due to gravity at the place.

Mass is the physical quantity on which the inertia of a body depends.

Mass is the amount of matter contained in the body whereas inertia is the state of body at complete rest or in motion.

Thus, the matter composition of the object determines the inertia of the object.

Ammonia, NH₃: 4
Atomicity is the total number of atoms present in one molecule of an element or a compound. In case of ammonia i.e. NH₃ , 4 atoms are present, therefore its atomicity is 4.

Mole Concept:

We know that a dozen is a collect ion of 12 substances, a century is a collection of 100 substances and a gross is a collection of 144 substances. We use the terms dozen, century, gross etc. to express a certain quantity of a substance. Similarly, a mole is a word used to describe a collection of particles i.e. atoms, molecules or ions.

1 mole of a substance is equal to its atomic mass or molecular mass expressed in grams. The atomic mass expressed in grams is the gram atomic mass. The molecular mass expressed in grams is the gram molecular mass.

For example, The atomic mass of sodium is 23 grams.

Therefore, 23 grams of sodium is equal to one mole of sodium atoms.

Similarly, the molecular mass of oxygen (O₂) =  2 × Atomic mass of oxygen

= 2 × 16

= 32 g

Avogadro experimentally found that one mole of any substance always contained 6.022 × 10²³ particles.

This number is called the Avogadro’s number, denoted by N₀.

Alpha particles are positively charged particles, having two protons and two neutrons and are identical to the nucleus of helium atom. They are spontaneously emitted by radioactive element.