Planets and OrbitsDo you know what is the meaning of the word

“Planet”?It means “wanderer”

Solar System It consists of a star as well as all the planets ,moons

and other bodies travelling around it

what keeps the planets revolve around the sun without wandering in

the outer space?

1)Gravity• It is the force of attraction among all objects .

• Gravity causes something you drop to fall to the floor ,and this same type of force keeps planets in orbits .

• The amount of gravitational force such as that between the sun and a planet depends on mass.

• The greater the mass of each object is ,the greater the attraction between them is

• Distance also is a gravitational factor ,the greater the distance is between the planet and the Sun ,the smaller

the pull of gravity .

2)Inertia• It is the second property that keeps planet in its orbit .• It is the tendency of a moving object to stay in motion .

•Gravity alone would pull the planets into the Sun ,because the sun has so much mass.• This doesn’t happen because the planets have “inertia”• Inertia alone ,however would cause the planets to move in straight line .

• The balance between inertia and force of gravity keeps the planet in their orbits around the sun .

• The planet would move in straight line because of its inertia ,but gravity pulls on the planets and curves their paths into orbits around the Sun

Ancient Explanation 1) Earth is considered to be the center

of universe .• According to this model ,the Sun ,the moon and the stars revolve around the

Earth

2)The other explanation stated that earth the moon,the stars and other planets revolve

around the Sun

•This idea better explained the motions of the planets

Comets • It is a ball of ice and rocks that orbits the Sun.• As a comet approaches the sun ,the sunlight warms the comet

ice causing the ice to turn to gas forming a cloud of gases.• Near the sun the radiations pushes the cloud away forming

comet tail which is always pointing away from the Sun .

Meteoroids• They are small rocky or metallic objects that orbits the Sun.

• The craters on the moon where formed by meteoroids collisions

Meteor • It is a meteoroid that enters Earth’s atmosphere, it appears as a bright streak in the sky .

Meteorite • If a meteor fails to break apart and burn up in the atmosphere it can hit Earth’s surface .•A meteoroids that strikes Earth’s surface is a meteorites