The Moon & Tides (77)

Tides

• Moon and sun contribute to the ocean’s tides.

• Gravity pulls the ocean water slightly & causes it to bulge out toward the moon. – Opposite side of bulge also slightly bulges

(due to earth’s rotation).– This is where high tide occurs.

Types of Tides

• High high (spring) tide: new and full moons, the moon and sun pull in similar directions (higher than normal tides).

• High tide: side facing the moon (or directly opposite).

• Low tide: side facing the sun (or directly opposite).• Low low (neap) tide: 1st and 3rd quarter moons, sun

and moon pull in opposite directions (lower than normal tides).

Result of Tides

• Water moving because of tides slows the earth’s rotation - 0.0015s/100years (days are getting longer).– Estimated that 900 million years ago the earth

had a 18 hour day.

Future of the Earth and Moon

• Earth also pulls on the moon.– Why the moon keeps the same side facing the

earth.• Over time the moon’s orbit is growing &

moves away ~4 cm/yr.– Measured by lasers.

Moon & Tides Diagram (76)• Draw 4 pictures of the earth, moon and

sun showing when we have the 2 spring tides and the 2 neap tides every month.

• Indicate the moon phase in each of the 4 pictures.

• Answer the following questions in complete sentences:

1. Explain why the earth has tides.2. Explain what the tides are doing to the

Earth’s rotation.