Human Activities Help Sustain Biodiversity and Ecosystem Services in a Changing World
developed by:
Julie Allender (OMSD), Colleen Duncan (Redlands USD), Dr. Vickie Harri (OMSD), Sara Yeh (OMSD)
Lesson 1: What causes tides (ESS1-1)
MS-ESS1-1: Develop and use a model of the Earth-sun-moon system to describe the cyclic patterns of lunar phases, eclipses of the sun and moon, and seasons. [Clarification Statement: Examples of models can be physical, graphical, or conceptual.]
Main Learning Goal: Students will learn how the relationships between sun, Earth-moon system affect tides and how kelp needs the tides to move nutrients around for other organisms that live within the kelp beds.
Focus Questions:
How does the sun, Earth and moon system affect tides? Why are the tides necessary to sustain a healthy kelp forest? Ideal student response to the focus questions: The gravitational pull of the sun and the moon cause high and low tides. The highest tides occur when the sun, Earth and moon are lined up in a straight line and lowest tides occur when the moon is at a right angle to the sun and Earth. Kelp forests require nutrients from the cold water that tides upwell. |
Science content storyline: Students have learned from IS2 how the sun/Earth/moon system causes phases of the moon and eclipses, and the role of gravity in determining motion within the solar system. This prior knowledge will lead into this lesson where students will learn how the gravitational force influences the tides. This lesson also informally introduces the characteristics of waves, which leads into Lesson 2 where students will formally learn this vocabulary.
Students will deepen their understanding of ecosystems, learned in 7th grade IS 3, to understand how best to sustain kelp ecosystems. |
1. Review Earth/Moon/Sun system model from IS 2.
Teacher Background:
This is a simplistic model of the effect of differential gravitational forces on the oceans. The moon exerts a much stronger pull on the water molecules closest to it. The molecules on the other side of the Earth receive a much weaker pull. In very simple terms, the difference in the moon's pull on the two sides of the Earth creates a stretched effect on the oceans. These pulling forces are called differential gravitational forces.
Teacher Background:
This is a simplistic model of the effect of differential gravitational forces on the oceans. The moon exerts a much stronger pull on the water molecules closest to it. The molecules on the other side of the Earth receive a much weaker pull. In very simple terms, the difference in the moon's pull on the two sides of the Earth creates a stretched effect on the oceans. These pulling forces are called differential gravitational forces.
2. Activity modified from https://naturebridge.org/sites/default/files/Gravity%20and%20Tides.pdf
Place a rubber band on a table in a circular shape. It represents the oceans. Now place one finger in the middle of the rubber band. The finger represents the Earth and ocean's center of gravity. Call the finger "e". Now place a finger from your other hand along the inside edge of the rubber band. This finger represents the force the moon Call this finger "m." Following a straight line, slowly pull m away from e. At this point, the rubber band stretches.
Questions to ask students:
What makes waves on the ocean?
What are tides?
What makes tides go up and down?
Does the moon have gravity?
Does the sun have gravity?
What effect does the moon's gravity have on the ocean?
Place a rubber band on a table in a circular shape. It represents the oceans. Now place one finger in the middle of the rubber band. The finger represents the Earth and ocean's center of gravity. Call the finger "e". Now place a finger from your other hand along the inside edge of the rubber band. This finger represents the force the moon Call this finger "m." Following a straight line, slowly pull m away from e. At this point, the rubber band stretches.
Questions to ask students:
What makes waves on the ocean?
What are tides?
What makes tides go up and down?
Does the moon have gravity?
Does the sun have gravity?
What effect does the moon's gravity have on the ocean?
3. Introduce causes of high and low tides.
Students analyze graphs and find relationships between tides from 3 locations (Atlantic, Gulf, Pacific) during a lunar cycle. Emphasis should be on the La Jolla graph if time is a factor. (Note: Times are on 24 hour clock, so 00:00 is midnight. This is critical info for students to be able to connect the level of water to the moon cycle.)
Questions to ask students:
What do you see in the graphs?
Why do you think the water level increases?
When do those changes occur? (About every 12 hours)
What do you remember from our previous unit about the moon and Earth system? (There is a gravitational relationship.)
This change in water level, because of the pull of gravity, is called tides. Can you work with your rubber band model and your group to explain how a low tide occurs? Record your thinking in your notebooks.
Students analyze graphs and find relationships between tides from 3 locations (Atlantic, Gulf, Pacific) during a lunar cycle. Emphasis should be on the La Jolla graph if time is a factor. (Note: Times are on 24 hour clock, so 00:00 is midnight. This is critical info for students to be able to connect the level of water to the moon cycle.)
Questions to ask students:
What do you see in the graphs?
Why do you think the water level increases?
When do those changes occur? (About every 12 hours)
What do you remember from our previous unit about the moon and Earth system? (There is a gravitational relationship.)
This change in water level, because of the pull of gravity, is called tides. Can you work with your rubber band model and your group to explain how a low tide occurs? Record your thinking in your notebooks.
4. Correlation between tides and waves/movement of water. Direct instruction between differences between waves, tides and ocean currents. (teacher information only)
Fundamental difference - All these 3 movements are water movements caused by different forces.
Wave - These are the surface waves that occur on the free surface of water bodies - oceans, seas, lakes, rivers etc. Created because of the wind drift
Tides - These are periodic rises and falls of large bodies of water. They are caused by the gravitational attraction between the Earth and the Moon.
Ocean Currents - These are the large masses of water moving in a specific direction in open oceans / seas uniformly. These are caused due to the differences in density, temperature, salinity of water at different places of oceans.
Fundamental difference - All these 3 movements are water movements caused by different forces.
Wave - These are the surface waves that occur on the free surface of water bodies - oceans, seas, lakes, rivers etc. Created because of the wind drift
Tides - These are periodic rises and falls of large bodies of water. They are caused by the gravitational attraction between the Earth and the Moon.
Ocean Currents - These are the large masses of water moving in a specific direction in open oceans / seas uniformly. These are caused due to the differences in density, temperature, salinity of water at different places of oceans.
Linking Question: How do you think kelp is related to tides?
Expected student response: We saw that the kelp was moving all at the same time and in the same direction. We think this is because of the tides.
Expected student response: We saw that the kelp was moving all at the same time and in the same direction. We think this is because of the tides.
Other summative/formative questions: (Note: We are working on increasing the rigor to a 2D question)
How does the sun, Earth and moon system affect tides?
Why are the tides necessary to sustain a healthy kelp forest?
How does the sun, Earth and moon system affect tides?
Why are the tides necessary to sustain a healthy kelp forest?
Additional Resources: NOAA has lessons on tides, complete with teacher directions and students worksheets. Up and Downs
A lot more info on waves and links to wave properties.
A lot more info on waves and links to wave properties.