7.9B The Solar System's Governing Authority

Gravity in Our Solar System 1:

Gravity Variables

Objective: I will be able to explain how mass and distance affect the force of gravity between two solar system bodies.

Open Ended

This model shows the earth-moon-sun system. Make at least one observation about the motion of these objects.

(Click the image to make it bigger)

Observations:

• The Earth orbits (revolves) around the Sun.

• The Moon orbits (revolves) around the Earth.

• The Earth takes about 365 "days" to orbit the Sun.

• The Moon orbits the Earth 12 times every 365 days (1 orbit = 365/12 = 30 days)

Motivating Questions:

Why is the Earth's orbit mainly influenced by the Sun?

Why is the Moon's orbit mainly influenced by the Earth?

Newton and Gravity

• By the time Newton shows up, much data on the motion of planets and moons had been collected.

• Kepler, a German astronomer, had developed mathematical laws that described planet motions.

• In 1687, Newton explains the motion of planets using his law of universal gravitation.

Variable 1: Mass

• If the less mass the objects have, the weaker the gravity will be between them.

• The more mass the objects have, the greater the gravity between them.

Multiple Choice

The ________ mass two objects have, the greater the gravity between them.

• more

• less

Multiple Choice

Which two objects would have a stronger gravitational attraction?

Multiple Choice

When a person drops a ball, it is attracted to the ground. Which statement best explains why the ball falls to the ground?

• The Earth has more mass than the person. The strength of gravity is stronger between the ball and the Earth.

• The Earth has more mass than the person. The strength of gravity is stronger between the person and the ball.

Variable 2: Distance

• The closer objects are, the stronger the gravity is between them.

• The farther apart objects are, the weaker the gravity is between them.

Multiple Choice

Gravity is weaker if objects are _____________.

• closer together

• farther apart

Multiple Choice

Which two objects would have a stronger gravitational attraction?

Multiple Choice

Which object will experience the weakest gravitational pull towards Object X?

• Object A

• Object B

• Object C

Motivating Questions

• Why is the Earth's orbit mainly influenced by the Sun?

• Why is the Moon's orbit mainly influenced by the Earth?

Open Ended

Base your answer to the following question on what you know about distance and gravity and the information in provided in the table.

Why does the Moon orbit the Earth and not the Sun?