Which of the following are characteristics of the Geocentric model of our solar system?

• Has 5 planets

• Has 8 planets

• Earth is at the center of the solar system

• The Sun is at the center of the solar system

• The planets travel in a circular orbit

Answer explanation

Aristotle and Ptolemy designed models of our solar system that included 5 planets: Mars, Jupiter, Saturn, Venus and Mercury (notice these are the ones we can see with our naked eyes). The Earth is placed at the center and the planets and Sun orbit it in a circular pattern.

Which characteristics are true of a heliocentric model of our solar system?

• Has 5 planets

• Has 8 planets

• The Sun is at the center of the solar system

• The planets travel in circular orbits

• The planets travel in elliptical orbits

Answer explanation

Advances in science and math helped Copernicus understand that the Sun is at the center of our solar system. He also determined that planets closer to the Sun orbit it faster than those farther away. The invention of the telescope helped us find new planets, and Kepler used math to better understand the orbits, and to show that they are elliptical, and off-center.

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Choose the correct statement about how Newton developed his ideas about universal gravitation.

• He built upon the science that others before him had developed

• He knew Copernicus and Hooke were wrong, so he looked for opposite ideas

• He and Kepler worked together on math equations.

• Newton was the first one to come up with the idea that the force of gravity increases as objects get closer together (the distance between them decreases).

Answer explanation

Newton built upon the work of many scientists that came before him. He did not live at the same time as Kepler- Kepler died before Newton was born. He did however sorrespond with Hooke, and used the work of Robert Hooke in his formulation of the law of Universal Gravitation- Hooke had developed an understanding of the inverse (opposite) relationship between gravity and distance, that gravity increases as distance decreases.

How did Johannes Kepler contribute to the Law of Universal Gravitation?

• He found that the path of planets as they orbit the Sun is elliptical

• He proposed the idea that there was an attractive force that kept planets in orbit, and applied to all objects in space.

• He used mathematical equations to prove that the force of gravity increases as the distance between 2 objects decreases

• He used math to prove that the Earth is at the center of the solar system

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How did Robert Hooke contribute to the Law of Universal Gravitation?

• He found that the path of planets as they orbit the Sun is elliptical

• He proposed the idea that there was an attractive force that kept planets in orbit, and applied to all objects in space.

• He used mathematical equations to prove that the force of gravity increases as the distance between 2 objects decreases

• He used math to prove that the Earth is at the center of the solar system

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How did Isaac Newton contribute to the Law of Universal Gravitation?

• He found that the path of planets as they orbit the Sun is elliptical

• He proposed the idea that there was an attractive force that kept planets in orbit, and applied to all objects in space.

• He used mathematical equations to prove that the force of gravity increases as the distance between 2 objects decreases

• He used math to prove that the Earth is at the center of the solar system

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Which planet has the most elliptical orbit?

• Earth

• Mars

• Venus

• Mercury

• Saturn

Why does a planet's speed decrease as it moves farther from the Sun along it's orbit?

• The direction of the Sun's pull on the planet changes as the planet orbits

• The Sun's gravitational force on the Sun decreases

• The planet's inertia changes

• The planet moves faster when it is farther from the Sun not slower.

Answer explanation

The diagram shows the real reason a planet’s speed changes along its orbit. Because of inertia, the planet always has a tendency to move along a straight line at a constant speed. As a planet moves toward the sun, the gravitational pull is generally forward, causing the planet to speed up. As a planet moves away from the sun, the gravitational pull is generally backward, causing the planet to slow down.

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Gravitational force is considered to be universal because...

• It is true for all objects

• It applies only to planets and moons

• It is true only for objects in our own solar system

• It acts only in one direction

Answer explanation

Universal means it is true for ALL objects, actually for all matter in the universe. Even atoms experience the force of gravity!

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Why were Copernicus' ideas considered controversial? Choose 3 correct answers.

• They contradicted the religious doctrine of the time

• They reduced Earth to just another planet, not the center of the universe

• His ideas were mostly incorrect, and his model was too complex.

• It contradicted the scientific understanding at the time

• There were no observations to support them