hat pattern.
- What do you notice about these pictures? There are four images of the Bay of Fundy (on the east coast of Canada) Two are satellite images, taken several months apart. Two were taken on the ground at different times on the same day. Each pair shows the water level at a different height, which in one image, left the boats grounded!
- Have you ever been to the coast and seen the ocean? Have you ever explored tide pools?
- What happens to the level of the ocean water over the course of a day? They rise and fall. In some places, this occurs once a day. In others, in occurs twice a day.
- What do we call this daily rise and fall of ocean waters along coastlines? Tides.
- What causes tides? The children may know that the Moon’s gravitational pull causes tides.
Add that the Sun's gravitational pull also helps create tides. However, the Moon's gravitational pull gives the tides their height and regular, daily pattern. An area's geographic location and the shape of the sea floor also affect the tide.
Facilitator's Note: There is a tricky distinction between waves and tides. The waves we like to watch breaking along the beach are caused by wind and are independent of tides. Tides cause the water level to be really high up on the beach, or really far out (often leaving clams and other sea life exposed), and everything in between.
A tidal wave, or tsunami, is caused by a sudden disturbance — such as an earthquake — and is unrelated to tides. If the conversation turns to tidal waves, gently clarify this distinction.
2. Explain that six children will model how the Moon’s gravitational pull creates tides. Because the Moon and Earth are in motion together as they orbit the Sun, this model will be similar to a dance. Have one child put on the T-shirt and represent the solid Earth. Have four other children wear blue T-shirts and stand in a circle around the "Earth": one behind, two on each side, and one directly in front of "Earth." These children represent Earth's oceans. The oceans are linked by four scarves or strips 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 