• The moon changes its shape everyday over a period one month and this repeats over and over again. These different shapes of the moon are called 'Phases of the Moon'. In reality, the moon does not change its shape at all. Moon is always round in shape. As we know the moon is always visible because it reflects the light from the sun.
• It goes from a perfect round circle and gradually reduces in size and further becomes a  no moon (as shown here). This takes about 15 days.  This is called waxing.
• Then the moon again begins to grow in size until it becomes a full moon. This takes another 15 days. This is called waning.
• The total span between 2 full moons is approximately 30 days nearly a month.
• At any point of time, the sun is able to illuminate only half part of the moon. The other half of the moon does not receive any portion of sunlight because of its spherical shape.
• Depending on the these positions of sun, moon, and the earth, different proportions of the illuminated moon faces the earth, causing the shape of the moon appearing to change as seen from earth.
• On a full moon day, when the moon appears as a bright complete circle, the earth is directly between the moon and the sun. The illuminated surface of the moon fully faces the earth, making the moon appear round.
• On a new moon phase, the moon is between the Sun and Earth. This means its light is not reflected to Earth. Instead, the light from the sun bounces back from the earth and causes a slight illumination on the moon.
• All shapes or the phases of the moon indicate  its position from the Sun and earth and how light behaves in relation to each.

  Mars (Mangal): It is the first outside the orbit of the earth. It is also known as red planet. It has two satellites.

 Jupiter (Brihaspati): It is the largest planet of the solar system. It has a large number of satellites (moons).

 Saturn (Shani): It appears yellowish in colour. It has beautiful rings. Saturn has a large number of satellites. It is least dense among all the planets.

 Uranus (Indra): Like Venus, Uranus also rotates from east to west. It has highly tilted rotational axis. So in its orbital motion Uranus appears to roll on its side.

 Neptune (Varun): It is the outermost planet of the solar system. It has two moons.

 Mercury (Budh): It is the smallest planet and nearest to the sun. Mercury has no satellite of its own.

        Venus (Shukra): It is nearest to the earth and is the brightest planet in the night sky. Venus has no moon or satellite of its own. It rotates from east to west while the earth rotates from west to east.

The characteristics of eight planets are:
1)Venus : Its surface is a brownish yellow colour because of its atmosphere which is composed of largely of sulphuric acid and CO2.
2)Mars: It takes 687 days to revolve around the sun.This planet is very hottest planet then other planets.
3)Uranus: It rotates the sun in 84 years, its size is 51,118 kilometers in diameter.
4)Neptune: It's size is 49,500 kilometres in diameter. It orbit the sun every 165 years.
5)Mercury:It is the closest planet to the sun,so its orbits the sun very quickly just in 88 days.It surface is grey to orange in colour and it is covered with craters.
6)Earth: Earth rotates the sun every 365 days(years) and rotates in its every axis in 24 hours(day). It size is a little more than 12000 km. In diameter. This planet is the different from the other planets as it maintains life on it.
7)Jupiter:It is the largest of the solar system as a diameter of 142,980.
8)Saturn:It is a large planet as 120,536.It's orbit the sun in 12 years.

Orbital period

The orbital period is the time a given astronomical object takes to complete one orbit around another object, and applies in astronomy usually to planets or asteroids orbiting the Sun, moons orbiting planets

rotation period 

The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) is the time that the object takes to complete a single revolution around its axis of rotation relative to the background stars. 

Since the planets are much nearer to us than the stars, they appear to be big and do not twinkle at night. The stars appear to twinkle at night but the planets do not twinkle at all. The planets move around the Sun from west to east, so the relative positions of the planets in the night sky keep changing day by day.

Wildlife sanctuary is the place where wild animals are protected in their natural habitat. Here poaching or capturing the animals is prohibited.

 Biosphere reserves are the area used to conserve biodiversity like plants, animals and microorganisms. It contains many wildlife sanctuaries and national parks.

ANSWER

Vocal cords and Layrnx vibrate whenever we speak.

When we speak muscles in the larynx bring the vocal cords together. As the air rushes from our lungs out through the larynx, the from portion of the vocal cords vibrate, producing a sound. The upper portion of our throat then modifies this sound to produce speech.

Artificial satellites are man-made objects that orbit the Earth and other planets in the Solar System. Soviet Sputnik 1 mission was the first artificial satellite that was launched in 1957.

Uses of artificial satellites

Some of the common uses of artificial satellites are as follows:

• They are used in communication
• They are used in weather forecasting system
• They are used in GPS (Global Positioning System)
• They are used to transport instruments and passengers to the space to perform experiments.

Life exists only on earth because of the following reasons:

• Earth has all the basic necessities that are required for an organism to survive
• The temperature and atmosphere of the earth makes life comfortable for the organism
• Earth is at an adequate distance from the sun which gives us heat that is neither too hot nor too cold
• Earth has enough amount of water, food and air for survival of living organisms
• Earth has a protective ozone layer which protect us from the harmful rays

Rayon, nylon, polyester, acrylic, and spandex are examples of synthetic fibres.

Fibres that are made by human beings are called synthetic fibres. Most synthetic fibres are obtained from coal, petroleum, and natural gas. A synthetic fibre consists of multiple units (each of which is a chemical substance), which are joined together to form a single unit called a polymer (poly: many; mer: unit). The structure of a polymer can be described as resembling numerous beads on a string, with the beads representing the individual units that are joined together.

The modern textile industry is unthinkable today without synthetic fibres. Man-made fibres like silk have always been greatly valued for its gloss and fineness. Man-made fibres are smooth. They can be distinguished by looking at a cross-section. Some synthetic fibres are listed below.

1. rayon
2. nylon
3. polyester

The cell membrane is also called the plasma membrane. It provides protection for the cell and its cellular components from the external environment. It is selectively permeable and regulates the movement of molecules in and out of the cell.

Gravitational force is a weak force unless large masses are involved. The masses of humans are quite small and thus the magnitude of gravitational force is also very small and negligible as compared to that shown by Earth. Thus, gravitational force exists between two people sitting close by but it is negligible and cannot be felt.

The Richter magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes.

A device called Seismograph is used to record seismic waves produced during earthquakes on the surface of the earth. The purpose is to measure the motion or movement of ground during an earthquake
The power of an earthquake is expressed in terms of a magnitude on a scale called Richter scale.
Destructive earthquakes generally have a magnitude of greater than 7 or 7.5. Earthquakes of magnitude 5-7 are moderate and below 5 are small or negligible.

Sometimes atoms gain or lose electrons. The atom then loses or gains a "negative" charge. These atoms are then called ions. Positive Ion - Occurs when an atom loses an electron (negative charge) it has more protons than electrons.

When the positive and negative charges grow large enough, a giant spark - lightning - occurs between thetwo charges within the cloud. This is like a static electricity sparks you see, but much bigger. Most lightninghappens inside a cloud, but sometimes it happens between thecloud and the ground.

When the positive and negative charges grow large enough, a giant spark - lightning - occurs between thetwo charges within the cloud. This is like a static electricity sparks you see, but much bigger. Most lightninghappens inside a cloud, but sometimes it happens between thecloud and the ground.

A N S W E R
To test if a body is charged or not, another uncharged body is brought in contact and seen whether the uncharged body is charged or not.

If a charged body (for example, ebonite rod) is touched to the metal disc of the gold-leaf electroscope, the metal strips of the electroscope gets charged by conduction. They repel each other and open up. In this way, we can detect whether an object is charged or not.

The process of charging a body by bringing a charged body near it without touching it is called charging by induction. In this process, the body being charged acquires the opposite kind of charge to that of the body charging it.

The sky above Earth appears to rotate because of the rotation of the Earth. The apparent fixed stars go East to West as the Earth rotates West to East. But since the axis of rotation of Earth passes through pole star, it is that point about which the sky rotates and hence the pole star appears fixed.

Sun is nearer to earth as composed to distance of other stars from the earth, the sun appears to be bigger and brighter.

Plastic use is increasing day by day and it is not only our country's problem it is worldwide problem because it is spoiling our environment rapidly . to overcome this situation we should put our hands together to stop usage of plastic in our daily life. As responsible citizens of our country help to protect our environment from plastic related pollution by following ways:

1 We should use jute bags and jute material instead of plastics.
2 We should not throw the plastics in the drain,river,ponds,lakes.
3  We should not burn plastics as this burning emits harmful gases and pollute the environment.

The reason behind the rapid rise in obesity in adults and children is the cheaply available foods and drinks high in fat, sugar, and salt. Overweight problem is prevalent in poor as well as rich countries.

The maximum displacement of a vibrating object from its Central position is called the amplitude of vibration. The amplitude actually tell us how far the vibrating object is displaced from its central position.

One of the major functions of cytoplasm is to enable cells to maintain their turgidity, which enables the cells to hold their shape. Other functions of cytoplasm are as follows:

• The jelly-like fluid of the cytoplasm is composed of salt and water and is present within the membrane of the cells and embeds all of the parts of the cells and organelles.
• The cytoplasm is home to many activities of the cell as it contains molecules, enzymes that are crucial in the break down of the waste.
• The cytoplasm also assists in metabolic activities.
• Cytoplasm provides shape to the cell. It fills up the cells thus enabling the organelles to remain in their position. The cells, without cytoplasm, would deflate and substances will not permeate easily from one to the other organelle.