MOTION IN THE WATER

Waves,Tides & Currents

#Waves

> A disturbance which moves through or
over the surface of a
fluid.

> Mostly caused by winds
(Also earthquakes, volcanoes, grav. pull)
#What Causes Tides?

1. Gravitational pull of
sun & moon on Earth

• Moon closer, therefore
> effect
• Like magnet, pulls
water away from
surface = TIDAL BULGE

2. Centrifugal Forces

• Produced by motions of
Earth, sun, & moon
• Bulge on opposite side
because centr. force
> pull of moon

>Form of great energy.

#Water Motion in Waves

1. Water travels in vertical
circular orbits
2. Wave moves, particles don’t!

#Size of Wind Generated
Waves

> Depends on 3 things:
★ Wind Speed
★ Wind Duration (length of time wind blows)
★“Fetch” Extent of open water across which the wind can blow.
Types of Waves

1. CHOP – Short period

2. SWELL – Long period (boat rolls; seasickness)

3. SWASH – water up beach

4. BACKWASH – back down
Tides

* The rhythmic rise and fall of the ocean’s water

High tide = rising,
incoming tide, flow

Low tide = receding,
outgoing tide, ebb

Slack tide = vertical
movement stops

#What Causes Tides?

1. Gravitational pull of
sun & moon on Earth

• Moon closer, therefore
> effect
• Like magnet, pulls
water away from
surface = TIDAL BULGE

2. Centrifugal Forces

• Produced by motions of
Earth, sun, & moon
• Bulge on opposite side
because centr. force
> pull of moon
Types of Tides

•Spring Tide
– Moon and sun are in direct line with one another
– Results in unusually   high tidal range
-Tidal Range = vertical
distance between high & low tides
Types of Tides

•2x’s/month

*Neap Tide

– sun and moon are at
right angles

-Pulls cancel each
other out – causes a
weak pull

– unusually low tidal
range

2 x’s / month

#Currents

• What are currents?
– Circulation water

• Causes
– Wind
– Rotating Earth
– Density Changes

              RIP CURRENT

– Caused by converging long-shore currents
– Very dangerous ; Red Flag – DO NOT fight rip current; swim parallel to shore to get out of channel.

        Deep Ocean Currents
(The Global Conveyor Belt – Currents)

Separated from surface currents by boundary called a “Thermohaline” (diff in densities).
Flow beneath surface; cross equator.
Move North to South.

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