ips of fabric that they are holding in their hands. Have all five children stand to face the sixth child, who wears the grey T-shirt and represents the Moon.
- What’s a model?
We use models to help us represent objects and systems so that we can study and understand them more easily. Scientists use computers to create models to study the complex interactions between the Sun, Earth, and Moon.
- Is this model showing the correct sizes of the Moon, Earth, or oceans relative to each other? No.
- Are their distances from each other correct? No.
Ask the children to recall the scale model that they constructed in Earth's Bright Neighbor: The Moon was held 15 inches (38.4 cm) from a blueberry-sized "Earth."
- When two people dance together, do they usually stand so far apart? No.
- How can the Moon influence Earth? Its gravity pulls on Earth.
Explain that while a pair of dancers has to actually touch each other in order to move together, moons and planets can influence each other’s spins and tilts from a distance. All objects that have mass have their own gravity, but only large objects — like planets — have enough gravity to influence each other from afar.
Facilitator's Note: Does the Moon's gravity pull on humans, too? The Moon's gravity affects humans, as well. The tug of the Moon's gravity decreases a person's weight by a few grams. These tides are inconsequential, however, compared to the much stronger pull of the Earth beneath our feet.
2. Ask the children to demonstrate how the Moon’s gravitational pull creates two tides in most coastal locations on Earth each day.
- Which part of the Earth and ocean is being pulled the most by the Moon? The child closest to the Moon (one of the “oceans”).
- Which part of the Earth and oceans is being pulled the least by the Moon? The child farthest from the Moon (another “ocean.”)
Have the "ocean" child nearest the "Moon" take three large steps toward him or her. "Earth" and the two "oceans" standing beside Earth take two large steps toward the "Moon." The "ocean" child furthest from the "Moon" takes one large step toward the Moon.
- Why did the oceans move toward the Moon? The Moon's gravity pulled on them.
- What happened to the oceans? They moved apart around the "Earth" to form an oval rather than a circle shape.
Explain that the water from the oceans has "piled up" under the Moon and directly opposite the Moon. The two children standing beside "Earth" represent parts of the ocean where there is less water.
- Where are the oceans at the highest levels? The "oceans" nearest and furthest from the “Moon.” Are the coastal areas next to those “oceans” seeing a high or low tide? High.
- How many sides of the Earth experience high tide at the same time? Two (in general). Which part of "solid Earth" is experiencing high tide right now? The part that is under the "piled up" oceans.
- Where is low tide? Near the "oceans" standing closest to "Earth."
Note which body parts — the arms or front and back — are experiencing “high tide” and which are experiencing “low tide.”
- Why did the “ocean” furthest from the Moon move the least? It was “left behind.”
Facilitator's Note: The formation of the second ocean bulge is simplified in this model and ignores subtle motions of the Earth. A more accurate and complete description is presented in the following sources. Note that the science content level of these sources is intended for an adult audience.
"Our Restless Tides," National Oceanographic and Atmospheric Administration (NOAA)
Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing "Hoax"
Philip Plait, John Wiley & Sons, Inc., 2002, ISBN 0471409766
Explain that the model demonstrates how the Moon produces two high tides and two low tides at the same time. The ocean furthest from the Moon is far enough away that it "feels less" of the Moon's gravitational pull.
- Is the solid Earth standing still, like in this model? No, it's spinning.
Invite "solid Earth" to spin about once on his or her axis (the line straight up from the floor to his or her head) a few times to demo