How Does Earth's Speed Change

About this printable How Does Earth's Speed Change science reading passage, NGSS-aligned (Grades 5-8)

This engaging 400-500 word science reading passage for middle school students (grades 6-8) explores how Earth's speed changes during its orbit around the Sun. Students will learn why Earth moves fastest in early January at perihelion and slowest in early July at aphelion, understanding the cause-and-effect relationship between distance and gravitational pull. The passage introduces Johannes Kepler's discoveries and explains how elliptical orbits affect planetary motion. Aligned to NGSS standards MS-ESS1-2 and MS-ESS1.B, this audio-integrated resource includes a differentiated version for struggling readers, Spanish translations, a comprehensive glossary of key terms, multiple-choice questions, writing activities, and graphic organizers. Students will develop scientific reasoning skills while exploring fundamental concepts about Earth's motion in space. The passage uses evidence-based language and real-world examples to help students understand how gravity influences orbital mechanics.

Written by Workybooks TeamPublished by Workybooks

Sample passage and quiz from How Does Earth's Speed Change

Why Earth Moves Faster in January

Earth's orbit showing perihelion, aphelion, and changing orbital speeds. — Earth moves faster near the Sun and slower farther away.

Earth's speed changes throughout the year as it travels around the Sun. The planet moves fastest in early January and slowest in early July. This speed difference happens because Earth follows an elliptical orbit, not a perfect circle. Scientists explain that the changing distance between Earth and the Sun causes these speed variations.

Earth reaches perihelion, its closest point to the Sun, around January 3 each year. At this position, Earth sits about 147 million kilometers from the Sun. The planet travels at approximately 30.3 kilometers per second during this time. Six months later, around July 4, Earth reaches aphelion, its farthest point from the Sun. The distance increases to about 152 million kilometers. Earth's speed drops to roughly 29.3 kilometers per second at this position.

The reason for this speed change involves gravity. When Earth moves closer to the Sun, the Sun's gravitational pull becomes stronger. This stronger pull causes Earth to speed up as it approaches perihelion. Evidence shows that objects closer to a massive body feel a greater gravitational force. When Earth moves farther away at aphelion, the gravitational pull weakens. The weaker force allows Earth to slow down slightly.

German astronomer Johannes Kepler discovered this pattern over 400 years ago. His observations led to Kepler's Second Law, which states that planets sweep out equal areas in equal times. This means a planet must move faster when closer to the Sun and slower when farther away. Kepler's work helped scientists understand that planetary motion follows predictable mathematical patterns.

This speed variation affects Earth in subtle ways. The difference between fastest and slowest speeds is about 1 kilometer per second. While this may seem small, it demonstrates how orbital mechanics work throughout our solar system. All planets with elliptical orbits experience similar speed changes. Understanding these patterns helps scientists predict planetary positions and plan space missions accurately.

Interesting Fact: Even though Earth moves fastest in January when the Northern Hemisphere experiences winter, the speed change does not cause seasons. Seasons result from Earth's tilted axis, not its varying orbital speed.