MasteringAstronomy Chapter 4

Do tides affect Earth's atmosphere?

Yes, because atmospheric gas has mass.

If the Moon were closer to Earth, high tides would: a. be higher than they are now. b. be lower than they are now. c. occur three or more times a day rather than twice a day.

a. be higher than they are now.

According to Newton's second law, the greater the force exerted on an object, the greater the object's _____. a. distance b. velocity c. acceleration d. mass

c. acceleration

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? a. because the Moon orbits Earth faster than Earth orbits the Sun b. because the gravitational force between Earth and the Moon is stronger than the gravitational force between Earth and the Sun c. because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun

c. because the gravitational attraction between Earth and the Moon varies more across Earth than does the gravitational attraction between Earth and the Sun The Sun exerts a stronger gravitational force on Earth, which is why Earth orbits the Sun. However, tides are caused by the variation in the gravitational attraction across Earth. Even though the gravitational attraction between Earth and the Moon is smaller than the attraction between Earth and the Sun, the Moon's much closer distance makes this attraction vary more across Earth. That is why tides are due primarily to the Moon, with only a secondary effect from the Sun.

The gravitational attraction between Earth and the Sun is __________ the gravitational attraction between Earth and the Moon.

stronger than

Consider the statement "There's no gravity in space." This statement is: a. Completely false. b. False if you are close to a planet or moon, but true in between the planets. c. Completely true.

a. Completely false.

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? Select all that apply. a. High tides are highest at both full moon and new moon. b. Low tides are lowest at both full moon and new moon. c. Low tides are highest at both full moon and new moon. d. High tides are highest at full moon and lowest at new moon. e. High tides are highest at first- and third-quarter moon. f. Low tides are highest at full moon and lowest at new moon.

a. High tides are highest at both full moon and new moon. b. Low tides are lowest at both full moon and new moon. As the video shows, the tidal bulges are largest and the tidal minima are smallest at full moon and new moon. Those are the times when the tidal forces of the Sun and Moon align (and therefore add to one another). Therefore, high tides are higher and low tides are lower at these times, which are called spring tides. (In contrast, we have neap tides at first- and third-quarter moons, when high tides are not as high and low tides are not as low.)

As shown in the video, Earth has two tidal bulges at all times. Approximately where are these bulges located? a. One faces the Moon and one faces the Sun. b. One faces the Moon and one faces opposite the Moon. c. One is over the Atlantic Ocean, and one is over the Pacific Ocean. d. Both are on lines perpendicular to the Earth-Moon line.

b. One faces the Moon and one faces opposite the Moon. The tidal bulges face toward and away from the Moon, because they are caused primarily by the gravitational attraction between Earth and the Moon. Friction explains why the bulges are slightly ahead of the Earth-Moon line, rather than directly on the Earth-Moon line. We'll ignore that detail for now.

Most people are familiar with the rise and fall of ocean tides. Do tides also affect land? a. Yes, land rises and falls with tides equally as high (and low) as the oceans. b. Yes, though land rises and falls by a much smaller amount than the oceans. c. No, tides only affect the oceans. d. No, tides can only affect liquids and gases, not solids.

b. Yes, though land rises and falls by a much smaller amount than the oceans. Tides affect the entire Earth, but they are much more noticeable for the oceans because water flows so much more easily than land. Still, the land rises and falls about 1 centimeter with the tides.

As an interstellar gas cloud shrinks in size, its gravitational potential energy: a. stays the same at all times. b. gradually transforms into other forms of energy. c. gradually grows larger.

b. gradually transforms into other forms of energy.

The force of gravity follows an inverse square law, meaning that the strength of the force declines with the square of the distance between two masses. But if the distances between pairs of objects are all the same, as in Part A, then the strength of gravity depends only on __________. a. the size of the larger mass in the pair b. the product of the two object masses (M1×M2M1×M2) c. the sum of the two object masses (M1+M2M1+M2) d. the size of the smaller mass in the pair

b. the product of the two object masses (M1×M2M1×M2)

Compared to its angular momentum when it is farthest from the Sun, Earth's angular momentum when it is nearest to the Sun is: a. less b. the same c. greater

b. the same

Newton's second law of motion states that force equals mass times acceleration, or F=ma. Suppose you have already calculated the gravitational force, which we will call Fg , attracting Earth and the Moon. Then the amount of acceleration of Earth due to this force is __________. a. Fg divided by the acceleration of the Earth b. Fg divided by the mass of the Moon c. Fg divided by the mass of the Earth d. Fg divided by the acceleration of the Moon

c. Fg divided by the mass of the Earth

According to Newton's third law __________. a. the gravitational force exerted by the asteroids on the left will be equal for each pair of objects because all the asteroids have the same mass b. the strength of the force that the object on the left exerts on the object on the right has to be exactly the same (but in an opposite direction) as the force the object on the right exerts on the object on the left c. to find the force on the object on the right, you just have to divide the asteroid mass by the mass of the object on the right

b. the strength of the force that the object on the left exerts on the object on the right has to be exactly the same (but in an opposite direction) as the force the object on the right exerts on the object on the left

According to the law of universal gravitation, what would happen to Earth if the Sun were somehow replaced by a black hole of the same mass? a. Earth would be quickly sucked into the black hole. b. Earth would slowly spiral in to the black hole. c. Earth's orbit would not change.

c. Earth's orbit would not change.

If Earth were twice as far from the Sun, the force of gravity attracting Earth to the Sun would be: a. twice as strong. b. half as strong. c. one-quarter as strong.

c. one-quarter as strong.

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 __________. a. the Moon and Earth both have equal accelerations, because the forces are equal b. Earth has a larger acceleration than the Moon, because it has a larger mass c. the Moon has a larger acceleration than Earth, because it has a smaller mass

c. the Moon has a larger acceleration than Earth, because it has a smaller mass Newton's second law of motion, F=ma, means that for a particular force F, the product mass x acceleration must always be the same. Therefore if mass is larger, acceleration must be smaller, and vice versa.

Any particular location on Earth experiences __________. a. one high tide and one low tide each day b. two high tides and two low tides each month c. two high tides and two low tides each day d. two sets of high and low tides in the ocean, but only one set on land e. one high tide and one low tide each month

c. two high tides and two low tides each day The video shows that any location on Earth passes through both tidal bulges and both tidal minima (the places where the tides are smallest) each day, which means two high tides and two low tides. Again, recall that this is true for both land and oceans, though tides are more noticeable in the oceans because water flows so much more readily than land.

Compared to their values on Earth, on another planet a. your mass and weight would both be the same. b. your weight would be the same but your mass would be different. c. your mass would be the same but your weight would be different.

c. your mass would be the same but your weight would be different.

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? a. The second tidal bulge is created by the Sun's gravity. b. The second tidal bulge is a rebound effect, created when water on the side facing the Moon falls back down and thereby pushes up the water on the opposite side of Earth. c. The second tidal bulge is created by the centrifugal force caused by Earth's rapid rotation. d. The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line.

d. The second tidal bulge arises because gravity weakens with distance, essentially stretching Earth along the Earth-Moon line. Tides are created by gravity, and the tidal force is caused by the fact that gravity weakens with distance. Therefore, the parts of Earth that are closer to the Moon feel a stronger gravitational attraction to the Moon, and the parts of Earth that are farther away feel a weaker gravitational attraction to the Moon. This varying gravitational attraction essentially stretches Earth along the Earth-Moon line, creating tidal bulges on both sides.

For the situations shown, the two objects we are concerned with are Earth and the spaceship, which both have constant masses. Therefore, the strength of gravity between them: __________.

decreases with the square of their distance apart

For the situations shown, the two objects we are concerned with are the Moon and the spaceship, which both have constant masses. Therefore, the strength of gravity between them __________.

decreases with the square of their distance apart

To calculate the gravitational force between two objects we __________, and then multiply by the gravitational constant G.

multiply the two masses, divide by their distance squared

In the video, high tide on Earth is represented by __________.

the two places where the light blue region is thickest