Welcome to the Welcome to the NeighborhoodNeighborhood

Our Solar SystemOur Solar System

What’s the difference between What’s the difference between rotation and revolution?rotation and revolution?

Each planet spins on its axis. Each planet spins on its axis. This spinning is called This spinning is called rotationrotation..

Q: How long does it take the Earth to Q: How long does it take the Earth to rotate on its axis once?rotate on its axis once?

A: Approximately every 24 hours. A: Approximately every 24 hours. This is equal to one day.This is equal to one day.

What’s the difference between What’s the difference between rotation and revolution?rotation and revolution?

Q: How much of the Q: How much of the Earth is facing the sun Earth is facing the sun at any time?at any time?

A: Half of the Earth A: Half of the Earth faces the sunfaces the sun

Half of the Earth has Half of the Earth has day and the other has day and the other has night.night.

What’s the difference between What’s the difference between rotation and revolution?rotation and revolution?

Q: What is the path that one body Q: What is the path that one body follows as it travels around another follows as it travels around another body is space is called?body is space is called?

A: OrbitA: Orbit

One complete trip along an orbit is One complete trip along an orbit is called a revolution.called a revolution.

What’s the difference between What’s the difference between rotation and revolution?rotation and revolution?

Q: Do all planets in our solar system Q: Do all planets in our solar system have the same period of revolution?have the same period of revolution?

A: No!A: No! Q: Which planet do you think has the Q: Which planet do you think has the

shortest period of revolution? shortest period of revolution? Longest?Longest?

What’s the difference between What’s the difference between rotation and revolution?rotation and revolution?

Q: How long is Q: How long is Earth’s period of Earth’s period of revolution (or the revolution (or the time it takes Earth time it takes Earth to orbit or revolve to orbit or revolve around the sun around the sun once)?once)?

A: One year = A: One year = 365.25 days365.25 days

How many revolutions have you made around the sun?

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RotationRotation = the spin of a body on its axis = the spin of a body on its axis

OrbitOrbit = the path that a body follows as it = the path that a body follows as it travels around another body in spacetravels around another body in space

RevolutionRevolution = the motion of a body that = the motion of a body that travels around another body in space; one travels around another body in space; one complete trip along an orbitcomplete trip along an orbit

Johannes Kepler (1571 – 1630)Johannes Kepler (1571 – 1630)

German astronomerGerman astronomer Influenced by the Influenced by the

CopernicusCopernicus Professor of mathematicsProfessor of mathematics Contemporary of GalileoContemporary of Galileo Described the orbit of MarsDescribed the orbit of Mars He wrote three laws that He wrote three laws that

are important to are important to astronomy and are known astronomy and are known as Kepler’s Lawsas Kepler’s Laws

Kepler’s LawsKepler’s Laws

1.1. Planets orbit the sun in an Planets orbit the sun in an elongated circle called an ellipseelongated circle called an ellipse

2.2. Planets move faster when they are Planets move faster when they are closer to the sun, and slower when closer to the sun, and slower when they are further awaythey are further away

3.3. Planets that are closer to the sun Planets that are closer to the sun orbit faster than planets farther orbit faster than planets farther awayaway

Sir Isaac Newton (1642 – 1727)Sir Isaac Newton (1642 – 1727) Newton was born in England Newton was born in England

the same year Galileo died.the same year Galileo died. He is the most influential He is the most influential

scientist who ever livedscientist who ever lived He defined the He defined the laws of motionlaws of motion

and and universal gravitationuniversal gravitation which he used to predict which he used to predict precisely the motions of stars, precisely the motions of stars, and the planets around the and the planets around the sun. sun.

Newton constructed the first Newton constructed the first reflecting telescope.reflecting telescope.

Universal GravitationUniversal Gravitation

An objects are attracted to each An objects are attracted to each other because of gravityother because of gravity

This attraction depends on the This attraction depends on the massmass of the two objects and the of the two objects and the distancedistance between thembetween them

The larger the masses of the two The larger the masses of the two objects and the closer they are to objects and the closer they are to each other, the greater the force of each other, the greater the force of gravity between themgravity between them

Gravitational force is the Gravitational force is the dominant force the determining dominant force the determining motions in the Solar System.motions in the Solar System.

Gravity keeps the planets in Gravity keeps the planets in orbit around the sun.orbit around the sun.

If gravity pulls If gravity pulls objects objects together, why together, why doesn’t the doesn’t the moon come moon come crashing into crashing into the Earth?the Earth?

Orbits Falling Down and AroundOrbits Falling Down and Around The moon has The moon has inertiainertia.. Newton's first law of motion states that Newton's first law of motion states that

"An object at rest tends to stay at rest and "An object at rest tends to stay at rest and an object in motion tends to stay in motion an object in motion tends to stay in motion with the same speed and in the same with the same speed and in the same direction unless acted upon by an direction unless acted upon by an unbalanced force." unbalanced force."

In other words, objects tend to "keep on In other words, objects tend to "keep on doing what they're doing." doing what they're doing."

This tendency to resist changes in their This tendency to resist changes in their state of motion is described as state of motion is described as inertiainertia..

Orbits Falling Down and AroundOrbits Falling Down and Around

Q: There is no air in space. What Q: There is no air in space. What effect do you think this has on the effect do you think this has on the moon’s inertia?moon’s inertia?

A: No air = no resistance. The moon A: No air = no resistance. The moon continues to move.continues to move.

Orbits Falling Down and AroundOrbits Falling Down and Around

Q: But what about gravity?Q: But what about gravity?

A: The combination of the moon’s A: The combination of the moon’s inertiainertia AND AND gravitygravity is what causes the moon to is what causes the moon to move in a circular path around the Earth.move in a circular path around the Earth.

Q: Is this why we revolve around the Sun Q: Is this why we revolve around the Sun in an elliptical orbit?in an elliptical orbit?

A: Yes!A: Yes!

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Kepler discovered that planets Kepler discovered that planets move faster when they . . . move faster when they . . .

A) are farther from the sun.A) are farther from the sun.B) are closer to the sun.B) are closer to the sun.C) have more mass.C) have more mass.D) rotate faster.D) rotate faster.

Answer:Answer:B) Planets move faster when they are B) Planets move faster when they are

closer to the sun.closer to the sun.

What is the difference between What is the difference between rotation and revolution?rotation and revolution?

RotationRotation = the spin of a body on its = the spin of a body on its axisaxis

RevolutionRevolution = the motion of a body = the motion of a body that travels around another body in that travels around another body in space; one complete trip along an space; one complete trip along an orbitorbit

What causes a day?What causes a day?

The rotation of the The rotation of the Earth once on its Earth once on its axis.axis.

It is approximately It is approximately 24 hours.24 hours.

What causes a year?What causes a year?

The revolution of The revolution of the Earth once the Earth once around the sun.around the sun.

It is approximately It is approximately 365.25 days.365.25 days.

On what two properties does On what two properties does the force of gravity between two the force of gravity between two

objects depend?objects depend? MassMass (the amount of matter in an (the amount of matter in an

object)object)

DistanceDistance (how far apart they are) (how far apart they are)

What two properties cause an What two properties cause an object to have an elliptical orbit?object to have an elliptical orbit?

InertiaInertia (an object in motion continues at (an object in motion continues at the same speed and direction, unless the same speed and direction, unless acted upon by a force)acted upon by a force)

GravityGravity (the force that causes to objects (the force that causes to objects to be pulled toward each other)to be pulled toward each other)

HomeworkHomework

Use pages 630 – Use pages 630 – 633 in your text 633 in your text book to complete book to complete the Guided the Guided Reading for this Reading for this section.section.

It is due tomorrow.It is due tomorrow.