Tides are the periodic rise and fall of ocean water levels, caused primarily by the gravitational forces of the moon and sun. High tides occur when water bulges towards the moon, while low tides happen in areas between high tides. Tides are influenced by the moon's position, resulting in two high tides and two low tides each day, with variations occurring due to the alignment of the sun, earth, and moon.

1. Tides
Tides
What are they?
What are they?
What are they caused by?
What are they caused by?
Are there different kinds of
Are there different kinds of
tides?
tides?

2. • Those of you who have spent some time
Those of you who have spent some time
on the beach have probably noticed that
on the beach have probably noticed that
the water level of the ocean does not stay
the water level of the ocean does not stay
the same all day long. Although waves
the same all day long. Although waves
continually wash the shore, the actual
continually wash the shore, the actual
water level changes as the day passes.
water level changes as the day passes.

3. • It rises for a period of
It rises for a period of
hours until it reaches
hours until it reaches
its highest level, and
its highest level, and
then it begins to fall,
then it begins to fall,
or recede, to its
or recede, to its
lowest level. This rise
lowest level. This rise
and fall of the ocean
and fall of the ocean
is known as the
is known as the tide
tide.
.
Its highest and
Its highest and
lowest levels are, of
lowest levels are, of
course called high
course called high
and low tides.
and low tides.

4. High Tide
High Tide Low Tide
Low Tide

5. Tides – What are they?
Tides – What are they?
• Tides are daily changes in the level of
Tides are daily changes in the level of
ocean water.
ocean water.
• They are the periodic rise and fall of the
They are the periodic rise and fall of the
water level in the oceans and other
water level in the oceans and other
large bodies of water.
large bodies of water.
• I wonder how often this periodic rise
I wonder how often this periodic rise
and fall happens each day?
and fall happens each day?

6. What causes tides?
What causes tides?
What moves ocean water?
What moves ocean water?
• Wind
Wind
• Earthquakes
Earthquakes
• Plate tectonics
Plate tectonics
• The dominant force that moves ocean
The dominant force that moves ocean
water is the gravitational forces from both
water is the gravitational forces from both
the
the sun
sun and the
and the moon
moon.
.

7. Early thoughts about what
Early thoughts about what
caused the tides.
caused the tides.
• Some believed the earth was a living
Some believed the earth was a living
animal and the tides a result of its
animal and the tides a result of its
breathing.
breathing.
• Others, who thought the ocean’s
Others, who thought the ocean’s
waters were the earth’s blood,
waters were the earth’s blood,
decided the tides were its pulse,
decided the tides were its pulse,
caused by the beating of its great
caused by the beating of its great
heart.
heart.

8. Early thoughts about what
Early thoughts about what
caused the tides.
caused the tides.
• Early followers of the religious prophet
Early followers of the religious prophet
Muhammad believed that the rise and fall
Muhammad believed that the rise and fall
of the waters were caused when the
of the waters were caused when the
“Angel of the Sea” placed his foot in and
“Angel of the Sea” placed his foot in and
out of the ocean.
out of the ocean.
• Primitive natives thought the tides were a
Primitive natives thought the tides were a
sign of a sea god’s anger and made human
sign of a sea god’s anger and made human
sacrifices to please him.
sacrifices to please him.

9. The Lure of the Moon
The Lure of the Moon
• The relationship between the phases of
The relationship between the phases of
the moon and the tides was discovered
the moon and the tides was discovered
more than 2,000 years ago!
more than 2,000 years ago!
• People of the time knew the moon had
People of the time knew the moon had
something to do with the tides, but they
something to do with the tides, but they
couldn’t explain why.
couldn’t explain why.

10. Sir Isaac Newton to the
Sir Isaac Newton to the
Rescue!
Rescue!
• Newton’s
Newton’s
Universal
Universal
Gravitation
Gravitation theory
theory
helped to explain
helped to explain
how the gravity of
how the gravity of
the moon (and
the moon (and
the sun) were
the sun) were
related to tides.
related to tides.

11. What causes tides?
What causes tides?
• The gravity of the moon pulls on
The gravity of the moon pulls on
everything on the Earth.
everything on the Earth.
• The moon’s gravitational pull on liquids
The moon’s gravitational pull on liquids
is much more noticeable than on solids.
is much more noticeable than on solids.
• Why? Because liquids move more easily
Why? Because liquids move more easily
than solids.
than solids.

12. What causes tides?
What causes tides?
• How often tides occur and the
How often tides occur and the
difference in tidal levels depend on the
difference in tidal levels depend on the
position of the moon as it revolves
position of the moon as it revolves
around the Earth.
around the Earth.
• The moon’s pull is strongest on the part
The moon’s pull is strongest on the part
of the Earth directly facing the moon.
of the Earth directly facing the moon.

13. High Tide
High Tide
• The part of the ocean directly facing the
The part of the ocean directly facing the
moon, bulges towards the moon.
moon, bulges towards the moon.
• There is a corresponding bulge on the
There is a corresponding bulge on the
opposite side of the Earth.
opposite side of the Earth.
• These bulges are called
These bulges are called high tide.
high tide.

14. Low Tide
Low Tide
• When high tides occur, water is drawn
When high tides occur, water is drawn
away from the area between the high
away from the area between the high
tides, which causes
tides, which causes low tides
low tides to occur.
to occur.

15. How often is there a change in
How often is there a change in
tides?
tides?
Try to figure it out . . .
Try to figure it out . . .
• High tides happen on opposite sides of
High tides happen on opposite sides of
the Earth.
the Earth.
• The Earth rotates once on its axis every
The Earth rotates once on its axis every
24 hours.
24 hours.
• How many high tides would any one
How many high tides would any one
place in the ocean experience each day?
place in the ocean experience each day?

16. Answer
Answer
• The periodic rise and
The periodic rise and
fall of the water level
fall of the water level
in the oceans and
in the oceans and
other large bodies of
other large bodies of
water happens . . .
water happens . . .
• Twice each day!
Twice each day!

17. What effect does the sun
What effect does the sun
have on tides?
have on tides?
• The sun is much larger than the moon.
The sun is much larger than the moon.
• The sun is farther away from the Earth
The sun is farther away from the Earth
than the moon.
than the moon.
Q: Which one (the sun or the moon) do
Q: Which one (the sun or the moon) do
you think has a bigger effect on tides?
you think has a bigger effect on tides?
A: The moon, just because it is closer.
A: The moon, just because it is closer.

18. Tidal Variations
Tidal Variations
• Tidal Range
Tidal Range = the difference in levels of
= the difference in levels of
ocean water at high tide and low tide.
ocean water at high tide and low tide.
• Tidal ranges vary greatly due to the
Tidal ranges vary greatly due to the
combined forces of the sun and the
combined forces of the sun and the
moon on the Earth
moon on the Earth
• It all depends on the position of the
It all depends on the position of the
Earth, moon, and the sun in space.
Earth, moon, and the sun in space.

19. Spring Tide
Spring Tide
• A tide with a large
A tide with a large
tidal range that
tidal range that
occurs two times a
occurs two times a
month (new moon
month (new moon
and full moon)
and full moon)
• Sun, Earth, and the
Sun, Earth, and the
moon are aligned
moon are aligned

20. Neap Tides
Neap Tides
• A tide of minimum
A tide of minimum
range that occurs
range that occurs
during the first and
during the first and
third quarters of the
third quarters of the
moon
moon
• The sun, Earth, and
The sun, Earth, and
moon form a 90
moon form a 90
degree angle
degree angle

21. Weird Science!
Weird Science!
• The moon also creates tides in our
The moon also creates tides in our
atmosphere
atmosphere
• They are called
They are called lunar winds
lunar winds
• They can be detected by studying slight
They can be detected by studying slight
periodic fluctuations in weather patters
periodic fluctuations in weather patters
• Very strange, indeed!
Very strange, indeed!

22. Review
Review
Q:
Q: What are tides?
What are tides?
• Tide
Tide = the periodic rise and fall of the water
= the periodic rise and fall of the water
level in the oceans and other large bodies of
level in the oceans and other large bodies of
water.
water.
Q:
Q: What is the dominant force that moves
What is the dominant force that moves
ocean water?
ocean water?
• The gravitational forces from both the
The gravitational forces from both the sun
sun
and the
and the moon
moon.
.

23. Review (cont’d)
Review (cont’d)
Q:
Q: Where is the moon’s pull is strongest
Where is the moon’s pull is strongest
on the Earth?
on the Earth?
• The moon’s pull is strongest on the part
The moon’s pull is strongest on the part
of the Earth directly facing the moon.
of the Earth directly facing the moon.

24. Review (cont’d)
Review (cont’d)
Q:
Q: Which one (the sun or the moon) has a
Which one (the sun or the moon) has a
bigger effect on tides?
bigger effect on tides?
• The moon
The moon

25. Review (cont’d)
Review (cont’d)
Q:
Q: What is the difference in levels of ocean
What is the difference in levels of ocean
water at high tide and low tide called?
water at high tide and low tide called?
• Tidal Range
Tidal Range
Q:
Q: Tidal ranges vary greatly due to the
Tidal ranges vary greatly due to the
combined forces of the _________ and the
combined forces of the _________ and the
________ on the Earth
________ on the Earth
• Sun, moon
Sun, moon

26. Review (cont’d)
Review (cont’d)
Q:
Q: How are the sun,
How are the sun,
Earth, and moon
Earth, and moon
situated in space so
situated in space so
that we experience a
that we experience a
spring tide?
spring tide?
• Sun, Earth, and the
Sun, Earth, and the
moon are aligned
moon are aligned

27. Review (cont’d)
Review (cont’d)
Q:
Q: How are the sun,
How are the sun,
Earth, and moon
Earth, and moon
situated in space so
situated in space so
that we experience a
that we experience a
neap tide?
neap tide?
• The sun, Earth, and
The sun, Earth, and
moon form a 90
moon form a 90
degree angle
degree angle