# Chapters 3 & 4

Flashcard maker : Julie Noel
Kepler’s First Law states…
that the orbit of each planet is an ellipse with the Sun at one focus
Kepler’s Second Law states…
that as a planet orbits the Sun, it sweeps out equal areas in equal times
Kepler’s Third Law states…
that a planet’s orbital period, p, is related to its average (semimajor axis) orbital distance, a, according to the mathematical relationship p^2 = a^3
as Galileo first recognized, Venus is…
full whenever it is on the opposite side of the Sun from Earth, although we cannot see the full Venus because it is close to the Sun in the sky
Imagine that Venus is in its full phase today. If we could see it, at what time would the full Venus be highest in the sky…
at noon
When would a new Venus be highest in the sky?
at noon
When would you expect to see Venus high in the sky at midnight?
never
Earth is located at one _____ of the Moon’s orbit.
focus
According to Kepler’s Second Law, Jupiter will be travelling most slowly around the Sun when at ________, and fastest when at ______.
aphelion; perihelion
Earth orbits in the shape of a(n) _______.
ellipse
The extent to which a planet’s orbit differs from a perfect circle is called its ________.
eccentricity
Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be _____.
greater than your normal weight at rest
If you are standing on a scale in an elevator, what exactly does the scale measure?
the force you exert on the scale
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
The light from Polaris travels through space in the form of ______ energy
Rapidly moving comets have more ______ energy than slowly moving ones
kinetic
An apple contains _______ ___________ energy that your body can convert into other forms of energy
chemical potential
Nuclear fusion in starts converts some of the ____-energy of hydrogen nuclei into light and heat
mass
Due to its much higher density, water heated to 80 degrees Celcius contains more _______ energy than air at the same temperature
thermal
An asteroid that is moving farther from the Sun is gaining _______ ___________ energy
gravitational potential
How did the Ptolemaic model explain the apparent retrograde motion of the planets?
The planets moved along small circles that moved on larger circles around the Earth.
True/False: Copernicus was the first person to suggest a Sun-centered solar system.
False
Suppose a comet orbits the Sun on a highly eccentric orbit with an average (semimajor axis) distance of 1 AU. How long does it take to complete each orbit, and how do we know?
Each orbit takes about 1 year, which we know from Kepler’s third law.
Galileo observed all of the following. Which observation offered direct proof of a planet orbiting the Sun?
Phases of Venus.
Earth is closer to the Sun in January than in July. Therefore, in accord with Kepler’s second law:
Earth travels faster in its orbit around the Sun in January than in July.
According to Kepler’s third law:
Jupiter orbits the Sun at a faster speed than Saturn.
Tycho Brahe’s contribution to astronomy included:
collecting data that enabled Kepler to discover the laws of planetary motion.
Galileo’s contribution to astronomy included:
making observations and conducting experiments that dispelled scientific objections to the Sun-centered model.
A scientific theory ________
must explain a wide range of observations or experiments, and must not be able to be proved true beyond doubt
As long as an object is not gaining or losing mass, a net force on the object will cause a change in _______
velocity
Why are astronauts weightless in the Space Station?
Because the Space Station is constantly in free-fall around the Earth
Momentum is defined as ________
mass times velocity
A net force acting on an object will always cause a change in the object’s _______
momentum
The planets never travel in a straight line as they orbit the Sun. According to Newton’s second law of motion, this must mean that _____
a force is acting on the planets
Consider the elliptical orbit of a comet around the Sun. Where in its orbit does it have the largest amount of total orbital energy?
It always has the same total orbital energy.
When a spinning ice skater pulls in his arms, he spins faster because _______
his angular momentum must be conserved, so reducing his radius must increase his speed of rotation
The energy attributed to an object by virtue of its motion is known as ________
kinetic energy
According to the universal law of gravitation, if you triple the distance between two objects, then the gravitational force between them _________
decreases by a factor of 9
Which of the following statements correctly describes the law of conservation of energy?
The total quantity of energy in the universe never changes.
Consider the statement “There’s no gravity in space.” This statement is:
Completely false.
If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be:
one-quarter as strong.

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