ASTR 263 - Chapter 4.4 - 4.5

As you watch the video, notice that the size of the tidal bulges varies with the Moon's phase, which depends on its orbital position relative to the Sun. Which of the following statement(s) accurately describe(s) this variation?

- High tides are highest at both full moon and new moon. - Low tides are lowest at both full moon and new moon.

Which statement must be true in order for a rocket to travel from Earth to another planet?

It must attain escape velocity from Earth.

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

Any particular location on Earth experiences ________.

two high tides and two low tides each day

As the cloud shrinks in size, its central temperature ________ as a result of its ________.

- increases - gravitational potential energy being converted to thermal energy

As the cloud shrinks in size, its rate of rotation ________ because ________.

- speeds up - its total angular momentum is conserved

Approximately where is it currently high tide on Earth?

On the portion of Earth facing directly toward the Moon and on the portion of Earth facing directly away from the Moon.

If the Moon were closer to Earth, high tides would:

be higher than they are now.

You have found that tides on Earth are determined primarily by the position of the Moon, with the Sun playing only a secondary role. Why does the Moon play a greater role in causing tides than the Sun?

because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun

The video shows a collapsing cloud of interstellar gas, which is held together by the mutual gravitational attraction of all the atoms and molecules that make up the cloud. As the cloud collapses, the overall force of gravity that draws the cloud inward ________ because ________.

- gradually becomes stronger - the strength of gravity follows an inverse square law with distance

If you actually performed and compared the two trials chosen in Part C, you would find that, while the basketball and marble would hit the ground at almost the same time, it would not quite be exact: The basketball would take slightly longer to fall to the ground than the marble. Why?

Because air resistance has a greater effect on the larger ball.

Assume you have completed the two trials chosen in Part A. Which of the following possible outcomes from the trials would support Newton's theory of gravity? Neglect effects of air resistance.

Both balls fall to the ground in the same amount of time.

Earth has two tidal bulges at all times. Approximately where are these bulges located?

One faces the Moon and one faces opposite the Moon.

Most people are familiar with the rise and fall of ocean tides. Do tides also affect land?

Yes, though land rises and falls by a much smaller amount than the oceans.

If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be:

one-quarter as strong.

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

Suppose that the Sun were to collapse from its current radius of about 700,000 km to a radius of only about 6000 km (about the radius of Earth). What would you expect to happen as a result?

A tremendous amount of gravitational potential energy would be converted into other forms of energy, and the Sun would spin much more rapidly.

Why is Newton's version of Kepler's third law so useful to astronomers?

It can be used to determine the masses of many distant objects.

Suppose that two asteroids are orbiting the Sun on nearly identical orbits, and they happen to pass close enough to each other to have their orbits altered by this gravitational encounter. If one of the asteroids ends up moving to an orbit that is closer to the Sun, what happens to the other asteroid?

It will end up on an orbit that is farther from the Sun.

Einstein's theory, like Newton's, predicts that, in the absence of air resistance, all objects should fall at the same rate regardless of their masses. Consider the following hypothetical experimental results. Which one would indicate a failure of Einstein's theory?

Scientists dropping balls on the Moon find that balls of different mass fall at slightly different rates.

One tidal bulge faces toward the Moon because that is where the gravitational attraction between Earth and the Moon is strongest. Which of the following best explains why there is also a second tidal bulge?

The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line.