Earth Science Rocks!Warm up

Question:

What happens to the movement of water as depth of ocean water increases?

Earth Science Rocks!• MYP Unit Question: How do we use

water?

• Standard: Recognize the significant role of water in Earth’s processes.

 • Essential Question: How do tides affect

ocean levels?

TIDES !!!

6-3

Oceanography & Astronomy Earth Science Campbell Middle School

So what causes tides?The word "tides" is a basic term used to define the alternating rise and fall in sea level with respect to the land. Tides are produced by the gravitational pull of the moon and the sun.

But wait there’s more...To a much smaller

extent, tides also occur in large lakes, the atmosphere, and even within the solid crust of the earth. Oklahoma rises and falls about 25 cm every day!

Tidal Bulges...

The liquid at point A is closer to the Moon and experiences a larger gravitational force than the Earth at point B or the ocean at point C. As a result it “bulges” out. But what about the bulge at point C…?

HIGH TIDEHIGH TIDE

LOW TIDE

LOW TIDE

The moon at work...• Loosely, we may

think of the bulge at point C as arising because the Earth is pulled away from the water on that side. The gravitational force exerted by the Moon at point B is larger than that exerted at point C.

How often do we have high tides and low tides?• Let’s figure it out…

Did you figure it out?

In general, there are 2 high tides and two low tides each day.

Because the Earth rotates more quickly than the moon revolves around the Earth, tides do not occur at the same time each day.

So why are tides not exactly 12 hours apart?After all, it takes the earth 24 hours to rotate once.

• Right…BUT, Since the moon moves around the Earth, it is not always in the same place at the same time each day. So, each day, the times for high and low tides change by 50 minutes.

• The timing of tidal events is related to the Earth's rotation and the revolution of the moon around the Earth. If the moon was stationary in space, the tidal cycle would be 24 hours long. However, the moon is in motion revolving around the Earth. One revolution takes about 27 days and adds about 50 minutes to the tidal cycle. As a result, the tidal period is 24 hours and 50 minutes in length.

O.K. Let’s make it simple…• We get one high tide every 12 hours

and 24 minutes

Spring & Neap Tides• The Moon doesn’t work

alone. Remember the Sun’s gravity also affects tides.

• SPRING TIDES The Sun & Moon may work together to produce higher than normal tides.

• NEAP TIDES The Sun & Moon may work against each other to produce lower than normal tides.

NEAP TIDE

SPRING TIDES

• Notice Spring & Neap tides only occur at certain phases of the moon.

How often do Spring & Neap tides occur?• Uh…I need to see

that picture again before I can answer that!

• I know the answer. Let’s move on.

• In fact, the effect of the Sun on Earth’s tides is less than half that of the Moon.

• There are over 400 stellar objects that exert a measurable pull on Earth’s oceans.

• Almost all are barely noticeable

• Why are ocean tides so different everywhere?"Because they depend on many factors including the geometry of your local coastline, and exactly where the Sun and Moon are located.

Wanna know more?

http://www.wiley.com/college/strahler/0471480533/animations/ch19_animations/animation3.html