Learn on PengiAmplify Science (California) Grade 5Chapter 2: Why is the sun up sometimes, but not other times?

Session 1: Earth's Shape and Gravity

Key Idea.

Section 1

Gravity Pulls to the Center

Key Idea

Earth is a sphere, like a giant ball. You might wonder why people on the "bottom" don't fall off. The answer is a force called gravity.

Gravity is an invisible pull that attracts everything toward the center of the Earth. It pulls on people, oceans, and even the air. This center-seeking force keeps everything anchored firmly to the surface.

Section 2

Redefining "Down"

Key Idea

Because gravity always pulls to the center, the direction "down" is not the same for everyone in space. "Down" simply means toward the ground beneath your feet.

For a person at the North Pole, down is toward the center. For a person at the South Pole, down is also toward the center. This means that relative to space, people on opposite sides of the world are standing feet-to-feet!

Section 3

Redefining "Up"

Key Idea

If "down" is toward the center, then up is the opposite direction. "Up" always points away from the center of the Earth and out toward the sky.

No matter where you stand on the globe, gravity ensures that you feel upright. This explains why we don't feel like we are hanging upside down, even if we are on the southern half of the planet.

Lesson overview

Expand to review the lesson summary and core properties.

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Section 1

Gravity Pulls to the Center

Key Idea

Earth is a sphere, like a giant ball. You might wonder why people on the "bottom" don't fall off. The answer is a force called gravity.

Gravity is an invisible pull that attracts everything toward the center of the Earth. It pulls on people, oceans, and even the air. This center-seeking force keeps everything anchored firmly to the surface.

Section 2

Redefining "Down"

Key Idea

Because gravity always pulls to the center, the direction "down" is not the same for everyone in space. "Down" simply means toward the ground beneath your feet.

For a person at the North Pole, down is toward the center. For a person at the South Pole, down is also toward the center. This means that relative to space, people on opposite sides of the world are standing feet-to-feet!

Section 3

Redefining "Up"

Key Idea

If "down" is toward the center, then up is the opposite direction. "Up" always points away from the center of the Earth and out toward the sky.

No matter where you stand on the globe, gravity ensures that you feel upright. This explains why we don't feel like we are hanging upside down, even if we are on the southern half of the planet.