Chapter 1 HW and Quiz

A circular orbit would have an eccentricity of

0

TF: During retrograde motion, planets actually stop and move backwards in space.

False

TF: Galileo's observations of the sky were made with the naked eye.

False

TF: Kepler's laws hold only for the six planets known in his time.

False

TF: The heliocentric model of the universe holds that Earth is at the center and everything else moves around it.

False

TF: The speed of a planet orbiting the Sun is independent of the planet's position in its orbit. The speed of a planet orbiting the Sun is independent of the planet's position in its orbit. true false

False

What was the greatest contribution of Tycho Brahe to astronomy?

He amassed a large number of precise measurements of stellar and planetary positions in the sky.

The force of gravity between two objects obeys which of the following relationships?

It is attractive and increases if their masses increase.

The three laws of planetary motion by _____ allowed us to predict planetary motion.

Kepler

_____'s theories were based on the very accurate observations made by _____.

Kepler, Tycho Brahe

How does orbital speed at aphelion compare to the speed at perihelion?

Lower

How did Copernicus' model explain the retrograde motions of the planets?

Planets orbit the Sun at different speeds. When an inner, faster-moving planet "passes" a slower outer one, the slower planet appears to move backwards.

What is the name given to the phenomenon in which the apparent motion of the superior planets sometimes reverses?

Retrograde motion

Kepler's second law of planetary motion states that a planet in orbit around the Sun will do which of the following?

Sweep out equal areas in equal times

If the distance beween the centers of two objects doubles, what happens to the gravitational pull between them if the masses do not change?

The force will decrease to one-fourth its previous size.

Which of the following was NOT one of the discoveries made by Galileo?

The shape of a planet's orbit is an ellipse.

TF: You throw a baseball to someone; before the ball is caught, it is temporarily in orbit around Earth's center.

True

Galileo found the rotation period of the Sun was approximately

a month

According to Kepler's second law, Jupiter will be traveling most slowly around the Sun when at

aphelion

If the distance between two asteroids is doubled, the gravitational force they exert on each other will

be one fourth as great

Figure 1.17 in the textbook (Gravity), showing the motion of a ball near Earth's surface, depicts how gravity

causes the ball to accelerate downward.

It often takes several itterations (modifications) to get a good theory. And while Copernicus's model (theory) was a big improvement over geocentric models (theories), it had one major flaw (the was later corrected by Kepler):

circular orbits.

The extent to which Mars' orbit differs from a perfect circle is called its

eccentricity

Earth orbits in the shape of a/an ____ around the Sun.

ellipse

Kepler's first law worked, where Copernicus' original heliocentric model failed, because Kepler described the orbits as

elliptical, not circular.

Earth is located at one _____ of the Moon's orbit.

focus

According to Newton's laws, the planets orbit the Sun due to _____.

gravity

Tycho Brahe's contribution to Kepler's Laws of Planetary Motion were

his detailed and accurate observations of the planets' positions.

Copernicus proposed a heliocentric model for the solar system primarily because ________.

it was much simpler than the Ptolemaic model

(In Kepler's third law the square of the period equals the cube of the semimajor axis ... see page 35. So IF the semimajor axis doubles the right hand side of the equation increases by a factor of 8. Now try this question!)) If Earth's orbit around the Sun were to double in size, the new "year" would be

more than 2 current Earth years.

According to Kepler's second law, Pluto will be traveling fastest around the Sun when at

perihelion

When a planet's orbit takes it closest to the Sun, it's called

perihelion.

The force of gravity varies with the

product of the two masses & inverse square of the distance separating the two bodies.

The mathematical form of Kepler's third law measures the period in years and the ______ in astronomical units (AU).

semimajor axis

According to Newton, the gravity of the _____ is needed to explain planetary orbits.

sun

Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________.

the Moon has a larger acceleration than Earth, because it has a smaller mass

An Astronomical Unit (AU) is _________.

the average distance between the Sun and Earth

A planet whose distance from the Sun is 3 AU would have an orbital period of how many Earth-years?

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