Earth's Movement in Space

Earth's Movement in Space

Multiple Choice

Earth spins on an imaginary line that passes from the North Pole to the South Pole. This is called Earth's ____________.

• horizon

• revolution

• rotation

• axis

​Explanation

• ​The imaginary line that runs between the North and South Poles is called the axis.

• The spinning of Earth on its axis is called "rotation".

• If you chose "horizon," you are thinking about the horizontal line that looks like it separates the sky from the ground.

• "Revolution" is an incorrect choice because it describes the movement of an object around another object.

Multiple Choice

The motion of Earth spinning around this imaginary line is called Earth's ______.

• axis

• rotation

• horizon

• revolution

Multiple Choice

What word is used to describe one object moving around another object?

• orbit

• gravity

• revolution

• rotation

​Explanation

The correct answer is “revolution.” Revolution is the movement of one object around another. An orbit is a path that an object takes when traveling around another object. The choice "gravity" is incorrect because gravity is the force that keeps Earth revolving around the sun. The choice "rotation" is incorrect because rotation describes Earth making one turn around its central line.

Multiple Select

What factors determine the strength of the force of gravity? Choose the two that apply.

• distance between the objects

• sizes of the objects

• masses of the objects

• weights of the objects

​Explanation

• The correct answers are “masses of the objects” and “distance between the objects.” Newton's law of universal gravitation states that every object in the universe attracts every other object. The strength of the force of gravity depends on the masses of the objects and the distance between the objects.

• If you chose "weights of the objects," you are confusing weight and mass. The mass of an object never changes, because mass is the amount of matter in an object. The weight of an object depends on how much gravitational pull there is on it.

• The choice "sizes of the objects" is incorrect because even if an object is small, it can have a large mass. For example, a large balloon has less mass than a small steel ball.

Multiple Choice

Why does the sun shine more directly on Earth’s Northern Hemisphere during the summer months?

• The rotation of the sun makes temperatures warmer.

• The tilt of Earth's axis tips the Northern Hemisphere toward the sun.

• The gravitational pull toward the sun is stronger in August.

• Earth's orbit is nearest to the sun in the summer.

​Explanation

The correct answer is "The tilt of Earth's axis points the Northern Hemisphere toward the sun." The 23.5° tilt of Earth's axis causes the seasons. This occurs because different parts of Earth are tilted toward the sun at different times of the year. If the axis was straight up and down, the amount of sunlight in a given place would be the same all year. The answer "rotation of the sun" is incorrect because the sun's rotation does not affect Earth's temperatures. "Gravitational pull" does not affect temperature. Gravitational pull keeps Earth in rotation around the sun, and it does not change during different times of the year. "Earth's orbit" also does not affect the seasons.

​Explanation

• ​The correct answers are "solstice" and "equinox." The solstice is the day when the sun appears at either its highest or lowest point in the sky. In the Northern Hemisphere, the summer solstice usually occurs on June 21, and we experience the longest day of the year. The winter solstice in the Northern Hemisphere usually occurs on December 21, and we experience the shortest day of the year. The equinox is the day when night and day are each 12 hours long. You can remember equinox because equi-, as in “equal,” is in the word, so equinox means an equal division between day and night. "Inertia" is incorrect because inertia is the tendency of an object to resist a change in motion. "Rotation" is incorrect because it describes the spinning of Earth on its axis.

Poll

How do you feel about your understanding of this lesson?