Gravity and the solar system

Gravity and the solar system

Kepler's First Law of Motion

• Orbit - The path that an object follows as it travels around another object in space

• Scientists thought those paths were circular

• Kepler realized that these paths were ellipses, not circular

• He also discovered that the sun was not at the center.

• The sun is at one "focus"

• The near point is called the perihelion

• The far point is called the aphelion

• Sun is at one FOCUS - not the center

• PERIHELION is the near side

• APHELION is the far side

• Orbit is an ELLIPSE

• Kepler's 1st law of planetary motion

Kepler's Second Law

• If a line connects the planet to the sun

• The area is equal - a planet sweeps out equal areas in equal times. In order for this to work it must move more rapidly in some areas and more slowly in others.

• See video clips, page 4

• Planet moves rapidly at perihelion

• It moves most slowly at aphelion

Kepler's 3rd Law

• Square of period of a planet's orbit (p) - the time needed for a planet to orbit the sun p²

• Directly proportional to the cube of the planet's average distance from the sun. (a³⁾

• This ratio is the same for all planets

• Planets that are closer to the sun orbit around it faster.

• 
  

GRAVITY

pulls from all directions to the center of a mass.

NEWTON's law of Universal Gravitation

Increase in mass of either or both objects will increase the force

NEWTON's Law Continued.

• If you increase the distance between the objects the force will...

• DECREASE

Multiple Select

Newton's law of universal gravitation depends on which of these?

• mass of the object

• size of the object

• composition of the object

• distance between the object

Multiple Choice

Planets move in what type of orbit?

• Circular

• Spiral

• Elliptical

• Random

Multiple Choice

In a planet's elliptical orbit, the point when it is nearest to the sun is the

• aphelion

• perihelion

• focus

• ellipse

Multiple Choice

According to Newton's second law of motion a planet is moving fastest when it is at the

• aphelion

• perihelion

• focus

• ellipse

Multiple Choice

Kepler's third law of planetary motion tells us that

• a planet in closer proximity to the sun will orbit the sun faster than a planet that is further

• a planet that is further from the sun will orbit the sun faster that a planet that is closer to the sun

• a planet that is closer to the sun will orbit the sun more slowly than a planet that is further from the sun.

• a planet that is further from the sun will rotate in a circular pattern.

Multiple Choice

has an atmosphere that protects life

• Mercury

• Venus

• Earth

• Mars

Multiple Choice

As the distance between objects decreases, gravity

• increases

• decreases

• stays the same

Multiple Choice

As the mass of objects increases, gravity

• increases

• decreases

• stays the same

Multiple Choice

The force of gravitational attraction between the Sun and Venus could be increased by reducing which of the following?

• The distance between the Sun and Venus

• the period of rotation of the Sun

• The mass of the Sun and Venus

• The speed of the orbit of Venus

Multiple Choice

What keeps planets in orbit around the Sun?

• the Sun's mass

• the Sun's period of rotation

• the Sun's gravitational force

• the Sun's color