Science 3rd prep. 1st term unit 3 lesson 2

The Solar SystemMillions of years ago, planets were originated in orbits around the sun to form what is known as the solar system.

The solar system The system consists of:

- the sun - Eight planets - Comets - Asteroids- Moons

** the planets and the other bodies were originated in solar system since 4600 million years ago.

** solar system extends over 12000 million km. in the space. ** sun is the center of solar system and it is the dominant body (total mass 99% of solar system)

Gravity in the solar systemNewton was the first one who discovered the earth's

gravitational force.

The law of gravitation explain two points:

** the movement of planets around the sun. ** the movement of the moon around the earth.

Newton’s law of universal gravitation.The force of attraction between two bodies is directly proportional to the product of their

masses and is inversely proportional to the square of the distance between them.

Then he proved that the gravitational force makes: Ms.Marim 1

The Solar system

Science 3rd prep. 1st term unit 3 lesson 21 – planets revolve around the sun in fixed orbits. 2 – the matter of each celestial body remains firm.

** if the gravitational force of celestial body was strong enough, it will attract gases towards itself forming atmospheric envelope around it.

** law of universal gravitation is one of the basic laws of the universe.

Question What happens if there is no attraction force between the sun and earth? The earth will leave its orbit and float in random fashion in space and this

will lead to destruction of the earth.

Exercise

1 – the metal sphere represents the planet. 2 – the hand represents the sun 3 – the thread represents the gravitational force. 4 – the path of the metal sphere represent the orbit.

Enriching information ** Gravity keeps planets in their orbits around the sun and moons in their orbits around the planets.

** the effect of gravity decreases by increasing the distance between the sun and the planet.

Science , technology and societyWeightlessness

The continuous force of the Earth’s gravity on our bodies gives us weight.

But, when you are inside a lift going downward fast, you feel that you are lighter in weight.

weightlessness occurs in the spacecraft as astronauts fall down inside it with the same speed so that they get weightless.

Note If the lift falls ( when the wire are cut) , you feel weightlessness.

Experiments are performed on both animals and plants in space to study the effects of weightlessness on them. Also,

specific scientific experiments are done as they cannot be done on surface of the Earth.

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Science 3rd prep. 1st term unit 3 lesson 2

Theories about the evolution of the solar system

There are many scientific and philosophical theories about the evolution of the solar system. They are about twenty theories

These theories (as we shall see) are still unproved and subject to change.

Astronomers think that the most widely accepted model for explaining the formation and evolution of our solar system is " the Solar Nebular Model" which states that :

** planets and other bodies were originated in the solar system from the matter that remained from the evolution of the sun as follow:

1 – the sun was surrounded by solar nebula which is a sphere of gases and dust.

2 – the solar nebula stated to rotate.

3 – during rotation , it turned into a flat rotating disk.

4 – most of the dust compressed forming four masses. (( mercury, Venus, earth and mars ))** some dust and ice combined with gases forming (( Jupiter, Saturn, Uranus and Neptune))

Solar nebulaIt is a sphere f gases and dust from which the planets of the solar system were originated.

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1-Nebular theory (Laplace 1796)

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Most important theories

1 – Nebular theory 2 – Crossing star theory The modern theory

Science 3rd prep. 1st term unit 3 lesson 2The French scientist Pierre Simon Laplace published a research entitled ((world order)) and that was in 1796. This research included a vision of Laplace about the evolution of the solar system.

This perception (which won great reputation for a century) has been affected by two observations.

1 -There is something that looks like clouds or nebula in the space. 2 -The space contains many cloudy rings surrounding some planets such as rings of Saturn.

Assumptions of nebular theory: The solar system was a glowing gaseous sphere revolving around itself. This sphere is

called nebula.

1 – the Nebula (glowing gaseous sphere) -Over the time, the nebula gradually lost its heat so its size contracted and its revolving speed around itself increased.

2- The gaseous rings

a. Under the effect of centrifugal force, the nebula lost its sphere form and became in a form of a flat rotating disk.

b. Parts got separated from the flat rotating disk to form gaseous rings that also rotate in the same direction in which the nebula rotates.

3-the formation of the solar system - These gaseous circles were formed after the planets of the solar system got cooled and frozen.

- The flaming mass that remained in the centre formed the sun.-

Nebula: It is a glowing gaseous sphere revolving around itself, from which the solar system was originated.

2-The crossing star theory (Chamberlain and Molten 1905)

The crossing star theory is based on some assumptions:The solar system was originally a big star which is the sun.

1- huge star approached the sun. 2-This star attracted the sun to it; an act which led to a great expansion in the part of the sun facing it.

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Science 3rd prep. 1st term unit 3 lesson 2 3-This expanded part was exploded which led to: ** a gaseous line was formed of a great length from the sun ** The sun escaped from the gravity of that star due to the explosion.

4-The gaseous line started to condense due to the attraction forces and then it cooled forming the planets.

The sun escaped from the gravity of the crossing star? Due to the explosion of the expanded part of the sun.

3-The modern theory of the world (Alfred Hale,1944)This theory is based on

- what is sometimes seen when a star glows for a short time to be one of the most shining stars in the sky.

- After a day or two, its glow disappears gradually to return as it was.

- The reason for that glow is not precisely known.

- It may be due to the explosion of the star as a result of nuclear reactions that occur so suddenly and violently that the star bombs huge amounts of gaseous materials. - Then, its size increases and accordingly its shining increases as well.

- When the bombed gases are cooled, its shining returns as it was.

Assumptions of Alfred Hale (modern theory)

The solar system was originally a star rather than the sun:

1-The existence of a star rotating near the sun

2-The star was exposed to explosion due to huge nuclear reactions. 3-The force of the explosion led to- the bombing of the star’s nucleus away from the gravity of the sun.-A cloud of gas remained

4 –the gaseous cloud subjected to cooling and contraction processes forming the mater of planets

5 – the attraction force of the sun controlled the orbits of planets around it.

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Science 3rd prep. 1st term unit 3 lesson 2

The difference in the length of the day and year from a planet to another The earth revolves around its axis in a period of time estimated at one earth day, and it revolves around the sun in a period of time estimated at one earth year.

Earth's day It is the time taken by earth planet to complete one rotation around its axis.

Earth's year It is the time taken by earth planet to complete one rotation around the sun.

Note - earth's years = 365.25 earth's day. - The earth's day = 24 earth's hour.

1 – Factored led to the difference in the length of the day: 1 -Radius of the planet earth.2 - Speed of the planet rotation around its axis.

Day ; it is the period taken by the planet to make one complete rotation around its axis.

2 – Factors led to the difference in the length of the year; 1 -Distance between the planet and the sun.

2- Speed of the planet rotation around the sun

Year : it is the period taken by the planet to make one complete rotation around the sun.

Activity:>>> Explaining the difference in the length of the year from a planet to another.

Tools Chalk to draw circles in the school playground.

Steps 1 -Go out the school playground with your classmates.

2-Choose five of your classmates different in weight and size.

3-One of your classmates stands in the middle of the playground (a).

4-Draw four circles with a united centre around that student.

5-Each student stands on one of the circles in a way that are on one straight line.

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Science 3rd prep. 1st term unit 3 lesson 2

6- Give a signal to students to start moving in a circle around the centre.

7-Assign the time that each student takes to make a complete rotation

8-What is the reason for the difference in the time each student takes to make a complete rotation

Observation At equal speed, the time that each student takes to make a complete rotation increases as the distance between the student and centre increase

ConclusionThe difference length of a year is due to:

1-Distance between the planet and the sun.2- Speed of the planet rotation around the sun.

Compared to the rest of planets of the solar system, astronomers managed to determine the day and year for each planet in terms of the earth day and year as shown in the following table

Rotation around the sun (earth year)

)Rotation around the axis (earth day)

Planet

0.2459Mercury0.62243Venus11The Earth1.91.03 Mars 12 0.41 Jupiter 29 0.43 Saturn 84 0.72 Uranus 165 0.67 Neptune

We can conclude that:The longest day is on Venus The shortest day is on JupiterThe longest year is on Neptune The shortest year is on Mercury

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Science 3rd prep. 1st term unit 3 lesson 2

Science , technology and society

Space suit:- The first astronauts wore one space suit for the trip.

- Today, they wear clothes that differ due to missions they perform.

- There is a space suit to travel back and forth.

- There is also a normal type of special clothes to be worn inside the spacecraft in its rotation.

The important instruments to study the outer spaceSpecial Equipments centered on earth and space in order to study the Sun.

1 – The solar telescopePlace : centered on the earth. Use : forms a picture of the sun.

This type of telescope works on reflecting the sun rays downward to a mirror in a tunnel under the Earth’s surface.

- the sunlight is gathered , then separated into a solar spectrum by the spectrometer(( device that shows the different light waves of the sun.))

- Astronomers got most of their information about the sun from the study of its spectra.

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Science 3rd prep. 1st term unit 3 lesson 2- a picture of sun is formed in a monitoring room where astronomers can study its light.

Modern equipmentsAstronomers use modern equipments on the surface of the Earth.

They also send them to space to get photos and information better than what surrounds us.

2- Telescopes

Telescopes rotating in orbits around the Earth are better than that are been on surface of the earth because :

- they can see celestial bodies more clearly. - They catch rays that can't be able to penetrate the earth's atmosphere.

Examples:

The Hubble telescope- The Hubble telescope was launched in April in 1990 . - It rotates around the earth at a height of 500 km. From its location, - it collects photos since millions of years .These photos allow astronomers an opportunity to study the evolution of the universe after the Big Bang.

- Astronauts on a space shuttle regularly maintain this telescope in space.

3 – spacecrafts: They revolve around other planets or land on them, sending discoveries to the earth.

Most telescopes and spacecrafts are controlled by computers from he surface of the earth.

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Science 3rd prep. 1st term unit 3 lesson 2

Questions on lesson:

Complete the following statements; 1 – the sun is the center of ……………………………. And it represents …………….. % of the total mass of the solar system. 2 – the solar system consists of ……………., eight planets, …………………… , comets and …………………..3 – the force of attraction between two objects is …………………………. Proportional to the product of their masses and is ……………………………. Proportional to the square of the distance between them. 4 – as the distance between the planet and the sun increases, the sun's gravitational force ………………………………. And its motion becomes ………………………………. 5 – planets and other bodies were originated in the solar system from the matter tht remained from the evolution of the …………………………. 6 – the solar nebula is considered a gaseous cloud of …………………. And ………………… gases and dust of iron rocks and …………………….. 7 – scientist Laplace has been affected by two observations which are presence of …………………. In the space and presence of rings of planet. 8 – the scientist who found Nebular theory about the evolution of the solar system is called……………………. 9 – according to nebular theory, the gaseous rings cooled down and frozen forming the …………………………………. , while the flaming mass remained is the ………………………… 10 – the scientist who established ………………………………… theory is Laplace. But the scientist who established the modern theory of the world is ……………………………… 11 – the earth revolves around ……………………. In a period of time estimated at one earth's day and it revolves around ………………………. In a period of time estimated at one earth's year. 12 –the difference of the length of a day from a plane to another is due to ……………….. and …………………………………. 13 – the difference of the length of a year from a planet to another is due to ……………………. And ………………………….. 14 – the shortest year is the year of ………………………. Planet. 15 – on Neptune , the year is ………………….. earth's year, while on ………………………. Is 84 earth's year. 16 - ………………………….. telescope is used in studying the sun from the earth's surface.

Choose the correct answer 1 – solar system extends over …………………………………. Kilometer in the space a. 15000 million b. 1500 million c. 12000 million d. 4600 million.

2 – planets rotate around the sun by the effect of the gravity of ……………………… a. the sun b.the Jupiter c.the earth d. the moon

3 - ……………………. Is the scientist who proved the presence of attraction force between any two objects in the space. a. Galileo b.Isaac Newton c. Max plank d. Einstein

4 – the gravitational force between tow objects in the space is inversely proportional to ………

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Science 3rd prep. 1st term unit 3 lesson 2a. the product of their volumes b. square of the distance between them. c. square of the mass of each object. d. no correct answer

5 – the weightlessness case takes place when the lift ……………………………. a. ascends with uniform speed. b. descends with uniform speed. c. descends with uniform acceleration. d. falls when the carrying wires are cut.

6 - …………………… is from the gases of solar nebula a. hydrogen b. oxygen c. Nitrogen d. carbon dioxide.

7 - ……………….. is from the components of the dust of solar nebula. a. iron b.rocks c. ice d. all of the choices.

8 – in crossing star theory, planets formed due to…………………….. a. expansion of the crossing star . b. explosion of a nebula. c. expansion of a gaseous line from the sun towards the crossing star. d. expansion of a gaseous line from the crossing star towards the sun.

9 – the scientist who found the modern theory about the evolution of the solar system is ……..a. chamberlain b. Moulten c. Alfred Hale d. Laplace.

10 – in modern theory , bombing he star nucleus away was due to ……………….. a. the force of gravity b. collision by asteroids. c. drop in temperature d. huge nuclear reactions.

11 – the time taken by Saturn planet to rotate around the sun is ………………….. a. 12 years. b. 29 years c. 84 years. d. 165 years.

12 – the day on …………………… planet is longer than its yeara. Neptune b. Venus c. Mars d. Uranus.

Give reasons for:

1 – sun is the dominant body in the solar system ? …………………………………………………………………………………………………………………………………..

2 – the constancy of the planets in their orbits around the sun. ……………………………………………………………………………………………………………………………………

3 – the nebula lost its sphere form and became in a form of a flat rotating disk?…………………………………………………………………………………………………………………………………..

4 – the difference in the length of the year from a planet to another? …………………………………………………………………………………………………………………………………..

5 –the longest year is on Neptune? …………………………………………………………………………………………………………………………………..

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Science 3rd prep. 1st term unit 3 lesson 26 – the year in Venus is shorter than its day? …………………………………………………………………………………………………………………………………….

7 – telescopes rotating around the earth are preferred than that on the earth's surface? …………………………………………………………………………………………………………………………………..

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