Question 1

Why do many people consider Isaac Newton one of the greatest scientists who ever lived?
A) He formulated the laws that govern all motion in the universe
B) He combined the work of Galileo, Brahe, and Kepler into one framework
C) He figured out the mathematical form of a law of universal gravity
D) all of the above
E) none of the above (not a, not b, not c)

Accepted Answer

Isaac Newton is considered one of the greatest scientists who ever lived because he formulated the laws that govern all motion in the universe, combined the work of Galileo, Brahe, and Kepler into one framework, and figured out the mathematical form of a law of universal gravity.

Question 2

In an ellipse, the ratio of the distance between the foci and the length of the major axis is called:
A) the eccentricity
B) the semi-major axis
C) perihelion
D) the astronomical unit
E) Newton's ratio

Accepted Answer

The ratio of the distance between the foci and the length of the major axis is called the eccentricity of the ellipse.

Question 3

When NASA and a group of astronomers sent up a spacecraft designed to find planets orbiting other stars, they named it after Kepler. Why was this an appropriate name?
A) Kepler used his telescope to find the first planet orbiting another star
B) Kepler was the first person to express the law of universal gravity in mathematical terms
C) Kepler figured out the rules of planetary motion, which planets in our solar system and planets elsewhere must obey
D) Kepler was the first person to suggest how to launch rockets into space
E) Kepler designed the first telescope ever built
3)2 Newton's Great Synthesis

Accepted Answer

Kepler's laws of planetary motion are fundamental in understanding how planets orbit stars, making the naming of a planet-hunting spacecraft after him very appropriate.

Question 4

When a planet, in its orbit, is closer to the Sun, it:
A) moves slower than average
B) reflects less sunlight than average
C) feels less gravitational pull than average
D) moves faster than average
E) spins faster on its axis

Accepted Answer

According to Kepler's Second Law, a planet in its orbit moves faster when it is closest to the Sun (referred to as perihelion) and slower when it is farthest from the Sun (referred to as aphelion). Therefore, when a planet is closer to the Sun, it moves faster than average.

Question 5

The idea that objects (in the absence of an outside force) tend to continue doing what they are already doing is called the law of
A) eccentricity
B) inertia
C) action-reaction
D) angular momentum
E) Congressional action

Accepted Answer

The law of inertia states that objects in motion tend to continue moving in a straight line at a constant speed, and objects at rest tend to remain at rest unless acted upon by an outside force. This is also known as Newton's First Law of Motion.

Question 6

To come up with the precise mathematical form of his law of gravity, Newton first had to invent the mathematical techniques that we now call:
A) algebra
B) ratio and proportions
C) angular momentum
D) calculus
E) scientific notation

Accepted Answer

Newton had to invent calculus to derive the precise mathematical form of his law of gravity.

Question 7

According to Kepler's third law, there is a relationship between the time a planet takes to revolve around the Sun and its
A) size
B) period of rotation
C) distance from the Sun
D) eccentricity
E) astrological sign

Accepted Answer

Kepler's third law states that the square of the period of revolution of a planet around the Sun is proportional to the cube of its average distance from the Sun. This means that there is a direct relationship between the time a planet takes to revolve around the Sun (its period) and its distance from the Sun. Therefore, choice C is the correct answer.

Question 8

Which of the following has the greatest density?
A) a cubic meter of snow
B) a cubic meter of air
C) a cubic meter of astronomy textbooks (the printed versions, not the on-line ones)
D) a cubic meter of feathers
E) a cubic meter of lead

Accepted Answer

Density is defined as mass per unit volume. Lead has a very high density, with a density of 11.34 grams per cubic centimeter. In comparison, snow has a density of approximately 0.1-0.5 grams per cubic centimeter, air has a density of approximately 0.0012 grams per cubic centimeter, textbooks have a density of approximately 0.6-1.5 grams per cubic centimeter, and feathers have a density of approximately 0.02-0.5 grams per cubic centimeter. Thus, the cubic meter of lead has the greatest density.

Question 9

After a long night of cramming for a test, your college room-mate hits his head forcefully against the wall of your room in despair. According to Newton's 3^rd Law, as he exerts a force against the wall, there must be an equal and opposite force. How does that opposite force show itself in this case? A) Your room-mate is pulled downward by gravity B) The wall exerts a force on your room-mate's head and he has a headache C) The wall has a huge dent in it D) There is an exception to the Law for solid objects like walls, so there is no opposite force E) The resident assistant assigned to your floor makes a complaint against the two of you 3)3 Newton's Universal Law of Gravitation

Accepted Answer

The wall exerts an equal and opposite force on your room-mate's head, which can result in a headache due to the impact. This is a direct application of Newton's Third Law of Motion, which states that for every action, there is an equal and opposite reaction.

Question 10

Why do astronauts (and cans of soft drink) float around in the Shuttle instead of falling?
A) the Shuttle is so far from the Earth, gravity is negligible
B) the Shuttle's gravity balances the Earth's, so that the net gravity is zero
C) the Shuttle is falling around the Earth (and everything aboard is in free fall)
D) the Shuttle has an antigravity device on board, developed by NASA
E) the rules Newton developed for gravity only hold on Earth, not once you get into space

Accepted Answer

The reason astronauts (and cans of soft drink) float around in the Shuttle is because the Shuttle is falling around the Earth, which causes everything on board to be in free fall. This creates the sensation of weightlessness, as there is no force preventing everything from the falling with the Shuttle. The gravitational pull of the Earth is still present, but is balanced by the Shuttle's velocity, which keeps it in a constant state of free fall.

Question 11

What specific event really made it possible for the three laws of planetary motion to be discovered?
A) a brilliant comet in 1601 blazed across the sky and was seen to cross in front of Venus
B) Tycho Brahe died and his assistant was able to get full access to his data
C) Galileo's books were published in Danish and became widely available to the public
D) an alignment of all the known planets in one part of the sky called everyone's attention to them
E) the plague broke out in England and forced Isaac Newton to return home from college

Accepted Answer

Tycho Brahe's death allowed his assistant, Johannes Kepler, to inherit all of his data and begin analyzing it. This data ultimately led Kepler to discover the three laws of planetary motion.

Question 12

Newton showed that to change the direction in which an object is moving, one needs to apply:
A) a force
B) an orbit
C) an inertia
D) a perigee
E) a bribe

Accepted Answer

According to Newton's first law of motion, an object at rest will stay at rest and an object in motion will continue to move in a straight line with constant velocity unless acted upon by an external force. Therefore, to change the direction in which an object is moving, one needs to apply a force.

Question 13

Astronomers discover a new comet that orbits the Sun, but has its aphelion (the furthest point in its orbit) beyond Neptune. Astronomers studying this comet have the right to expect that it:
A) will follow Newton's laws of motion
B) will move ahead in a straight line at a steady speed because of the law of inertia
C) will not obey Newton's universal law of gravitation
D) will not have an equal and opposite force in empty space when the force of the Sun's gravity pulls on it
E) astronomer have no right to expect ANY of the above.

Accepted Answer

The discovery of a new comet that orbits the Sun, but has its aphelion beyond Neptune, does not change the fact that all objects in space follow Newton's laws of motion. The comet will still obey these laws, including the universal law of gravitation, and experience an equal and opposite force when the force of the Sun's gravity pulls on it. Therefore, option A is the best choice. Option B is incorrect as the comet will not move in a straight line at a steady speed, as it will be influenced by the gravity of other planets in the Solar System. Option C is incorrect as the comet will still obey Newton’s universal law of gravitation. Option D is incorrect as the comet will still experience an equal and opposite force in empty space when the force of the Sun’s gravity pulls on it. Option E is incorrect as astronomers have the right to expect that the comet will follow basic laws of physics.

Question 14

An astronomy textbook, when printed out, weighs four pounds on the surface of the Earth. After finishing your course, you are so tired of the book, you arrange for NASA to shoot it into space. When it is twice as far from the center of the Earth than when you were reading it, what would it weigh? (Note, assume that the book has been moving away from the Earth, not falling freely around it.)
A) 4 lbs
B) 8 lbs
C) 2 lbs
D) 1 lb
E) 16 lbs

Accepted Answer

The weight of an object in space is determined by the force of gravity acting upon it, which is a function of the mass and distance between two objects. As the book moves away from Earth, the distance between it and Earth increases, causing the force of gravity to decrease. When the book is twice as far from the center of the Earth, the distance between it and Earth has doubled, causing the force of gravity to decrease to one-fourth of what it was before. Therefore, the book would weigh one-fourth of its original weight, or 1 pound.

Question 15

Which of the following statements about the force of gravity is FALSE?
A) it is a universal force, which acts everywhere in space
B) its strength decreases as the square of the distance
C) its strength is inversely proportional to the mass: the more mass, the less gravity
D) the force never becomes zero
E) it causes the paths of the planets to be ellipses and not straight lines

Accepted Answer

This statement is false. The force of gravity is directly proportional to mass; the more mass an object has, the stronger its gravitational force.

Question 16

Which of the following statements about forces is FALSE?
A) forces change the momentum of a body
B) forces cause an acceleration to take place
C) forces always occur in equal and opposite pairs
D) where there is no force, objects continue to move the way they were moving
E) there are places on Earth where all forces are absent

Accepted Answer

Option E is false as there are no places on Earth where all forces are absent. There is always at least the force of gravity acting on objects.

Question 17

In Newton's Law of Gravity, the force of gravity goes up as the:
A) mass goes down
B) distance goes up
C) mass goes up
D) distance goes down
E) more than one of the above

Accepted Answer

Newton's Law of Gravity states that the gravitational force between two objects is directly proportional to the product of their masses (C) and inversely proportional to the square of the distance between their centers (D). Therefore, as mass increases or distance decreases, the gravitational force increases.

Question 18

The 17th century astronomer who kept a roughly 20 year continuous record of the positions of the Sun, Moon, and planets was:
A) Tycho Brahe
B) Galileo Galilei
C) Isaac Newton
D) Nicolaus Copernicus
E) Jean Luc Picard

Accepted Answer

The astronomer who kept a roughly 20 year continuous record of the positions of the Sun, Moon, and planets was Tycho Brahe, who was active in the 17th century. Galileo Galilei was also active during this time, but his work primarily focused on the study of the heavens through the use of the telescope. Isaac Newton lived a bit later, in the 18th century, and his work was primarily theoretical in nature. Nicolaus Copernicus was active in the 16th century, prior to the time period in question. Jean Luc Picard, on the other hand, is a fictional character from the television show Star Trek and has no relation to astronomy.

Question 19

A single star in the process of forming starts by spinning slowly (while it is quite large and relatively cool.) As the star collapses under the pull of its own gravity, its size decreases. As a result, its rate of spinning:
A) will increase
B) will decrease
C) will stay the same
D) will either increase or decrease depending on the star's temperature
E) this question cannot be answered from the information we are given

Accepted Answer

According to the conservation of angular momentum, the rate of spinning (angular velocity) of a spinning object increases as its size decreases. This is due to the conservation of angular momentum which states that the product of the moment of inertia and the angular velocity must be conserved. Therefore, as the star collapses and its size decreases, its moment of inertia decreases, causing its rate of spinning to increase.

Question 20

We now know that the orbit of a stable planet around a star like the Sun is always in the shape of:
A) a circle
B) a parabola
C) a straight line
D) an ellipse
E) none of the above

Accepted Answer

Kepler's laws of planetary motion tell us that the orbit of a planet around a star is always an ellipse, with the star located at one of the two foci of the ellipse. This is one of the most important discoveries in astronomy, and has allowed scientists to accurately predict the positions of planets in our solar system and in others.

Quiz 3: Orbits and Gravity

Why do many people consider Isaac Newton one of the greatest scientists who ever lived?

In an ellipse, the ratio of the distance between the foci and the length of the major axis is called:

When NASA and a group of astronomers sent up a spacecraft designed to find planets orbiting other stars, they named it after Kepler. Why was this an appropriate name?

When a planet, in its orbit, is closer to the Sun, it:

The idea that objects (in the absence of an outside force) tend to continue doing what they are already doing is called the law of

To come up with the precise mathematical form of his law of gravity, Newton first had to invent the mathematical techniques that we now call:

According to Kepler's third law, there is a relationship between the time a planet takes to revolve around the Sun and its

Which of the following has the greatest density?

Why do astronauts (and cans of soft drink) float around in the Shuttle instead of falling?

What specific event really made it possible for the three laws of planetary motion to be discovered?

Newton showed that to change the direction in which an object is moving, one needs to apply:

Astronomers discover a new comet that orbits the Sun, but has its aphelion (the furthest point in its orbit) beyond Neptune. Astronomers studying this comet have the right to expect that it:

Which of the following statements about the force of gravity is FALSE?

Which of the following statements about forces is FALSE?

In Newton's Law of Gravity, the force of gravity goes up as the:

The 17th century astronomer who kept a roughly 20 year continuous record of the positions of the Sun, Moon, and planets was:

A single star in the process of forming starts by spinning slowly (while it is quite large and relatively cool.) As the star collapses under the pull of its own gravity, its size decreases. As a result, its rate of spinning:

We now know that the orbit of a stable planet around a star like the Sun is always in the shape of: