Tides
Chapter 13.2 & 19.2
Pages 434-437 & 654
Tides
• The rise and fall of Earth’s water on its
coastlines.
– High tide- water is at the highest point.
– Low tide- water is at the lowest point.
Cause of Tides
• Caused by the interaction of the Earth,
moon and sun.
• Gravity- pulls the moon and Earth
(including the water) towards each
other.
Cause of Tides
• As Earth rotates, different places on the
planet pass through the areas of tidal
bulges and experience the change of
water levels.
Cause of Tides
• Two Tidal Bulges form: resulting in two
high tides on Earth:
– One on the side of the moon- due to the
moon’s gravity
– One on the opposite side- more complex
reason, but the water is left behind
• Two low tides occur in the places
between the bulges.
Monthly
Daily Tide
TideCycle
Cycle
• High tides occur about 12 hrs and 25
minutes apart.
– Not every place has two regular tides a
day.
– Depends on the shape of bays, inlets and
the ocean floor.
Monthly Tide Cycle
• The Sun also impacts tides even
though it is 150million km away.
– The sun also pulls the water on the Earth’s
surface.
Spring Tides
• Twice a month- New Moon and Full
Moon
– Sun and Moon’s gravitational force
combine
– Results in really high tides and really low
tides.
Neap Tides
• Twice a month- First and Third Quarter
Moon
– Sun and Moon pull at right angles to each
other.
– Results in a tide with little difference
between low and high tide.
– Even outs the tides.