Gravity

What Are We Learning?

8ESS1.2 Explain the role of gravity in the formation of our sun and planets. Extend this explanation to address gravity’s effect on the motion of celestial objects in our solar system and Earth’s ocean tides.

The attractive force between all things that have mass

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What is Gravity?

​Gravity is ALWAYS a pull-never a push

Gravity is what keeps the Earth and other planets in orbit around the sun.

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​The sun has so much mass that it exerts a gravitational force on our entire solar system, keeping all of the planets, including Earth, in orbit.

​The moon is in constant motion.

The Earth and the Moon

​The moon rotates and revolves at the same speed- we see the same face of the moon all the time.

The moon glows at night because it reflects sunlight.

The sun always lights half of the moon, but because the positions of the Earth and moon change, we see a different part of the lighted side of the moon every night.

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When the moon is getting smaller in appearance, it is waning ("shrinking")

When the moon is getting larger in appearance each night, it is waxing ("growing")

​The moon is waxing from the new moon until the full moon and is waning from the full moon until the new moon. This is called a lunar cycle (which is 29.5 days)

The Earth's gravity pulls on the moon, keeping it in orbit, the moon's gravity also pulls on the Earth, causing tides.

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Ocean Tides

​Tides are the regular rise and fall of ocean water levels.

​The part of Earth that is either close to the moon or directly opposite the part facing the moon experiences high tide.

​The water is being pulled toward the moon.

When Earth, the sun and the moon are all lined up, the gravity of the moon and the sun add up, resulting in higher high tides and lower low tides, called Spring Tides.

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​When the sun and the moon are at a 90-degree angle to each other relative to the Earth, the gravitational forces are not aligned, so the don't add up, resulting in Neap Tides.