Modeling the Tides
Lesson at a glance: Students will make a model of the Sun, Moon and Earth to explain tides.
Goal: Students will be able to explain how the Sun and Moon’s gravitation pull creates tides.
Oregon Content Standards:
Science
2.2E.1 Observe and record the patterns of apparent movement of the sun and the moon.
Ocean Literacy Principles
1. The Earth has one big ocean with many features.
5.H. Tides, waves and predation cause vertical zonation patterns along the shore, influencing the distribution and diversity of organisms.
Materials:
- A wide-open area
Estimated Time: 45 minutes
Activity:
1. Discuss with students what they know about the movement of the Earth, Moon, and Tides. Ask students to share why they think the tides rise and fall. Tell students that they will work together as a class to make a human model to understand the tides.
2. Select a wide-open area to conduct the activity, such as a field, cafeteria, or gym. If you can find a painted circle on the ground, that will help.
3. Select one student to be the Moon. Select four students to be the Earth. Tell students that the Earth is about four times as big as the Moon.
4. Have students representing the Earth to form a circle, facing outwards and the Moon off to the side.
5. Select four students to be the Oceans of the Earth. Each Ocean student stands in front of an Earth student, both facing the same direction. Have Ocean students link elbows and remind them that all the oceans on Earth are connected.
6. Have the Earth students rest their hands lightly on the shoulders of the Ocean student in front of him or her. Explain that gravity holds the ocean to the Earth.
7. All other students are the Sun. Remind students that 109 Earths would fit in the sun. Imagine with your students how many classes would have to be the Sun in order for this model to be accurate. Have Sun students form a circle, facing outwards and linking elbows. They can wave their fingers to show the rays of light and heat from the Sun.
8. The Earth rotates on its axis in one complete circle every day. Have students who represent the Earth walk slowly in a tight circle to represent the rotation of the Earth. They will hold gently onto their Ocean student, so the “Ocean” will go with them.
9. The Sun rotates just as the Earth rotates, so have your Sun students rotate in a circle. The Sun rotates once every 27 days at the equator.
10. The Moon rotates at just the right speed so that it always keeps one face pointed toward the Earth. Have the Moon student rotate slowly around the Earth so that his or her face is always pointed towards the Earth.
11. After all students have practiced rotating, have them stop, sit where they are, and listen to you explain how the oceans are affected by the gravity of the Sun and Moon.
· The Earth has gravity that keeps the Oceans from floating off into space. This gravity is strong and the Oceans will never float away.
· The Sun and the Moon have gravity, too. They pull on the Earth’s oceans. Their pull is strong enough to make the Oceans bulge towards them, but not strong enough to pull the Oceans off into space.
· When the oceans are bulging towards the Moon or Sun, the water pulls away from the coastlines, creating low tides. When the oceans return to normal, the water covers the coastlines again, creating high tides.
12. Have students practice this gravitational effect. The Moon, Earth and Ocean students stand again and return to their positions. Have the Moon rotate around the Earth, wiggling his or her fingers to represent gravity. When the Moon student faces an Ocean student, have that student take three small steps towards him or her. After the Moon passes, the Ocean students should return to right in front of the Earth student holding onto their shoulder.
13. Now have the Sun students stand. Sun students can wiggle their fingers, too, now representing heat, light, and gravity.
14. If the Sun and the Moon are in alignment, the Ocean students should take four small steps towards them. That is called a Spring Tide and creates the highest high tide. This always happens when the Moon either full or new.
15. If the Sun and Moon are pulling in opposite directions, they cancel each other’s effect to some extent. The result is a much smaller tide and is called a Neap Tide. This always happens during quarter Moon phases.
16. Try the activity again with the class several more times, allowing students to switch roles.
Conclusions:
1. Review that Earth’s gravity holds the oceans onto the Earth, and the Moon and Sun’s gravity pulls the ocean towards them.
2. Review that when the ocean bulges towards the Sun or Moon, it pulls away from the coastlines causing low tides.
Extension:
1. Have students create a sketch showing the Earth, the Moon, and the tides.
2. This activity can also be used to show the orbit of the Earth around the Sun, the solar system, help explain night and day, or eclipses. For more information about tides, go to: http://home.hiwaay.net/~krcool/Astro/moon/moontides/