TidesTidesWhat 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?

• 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 the water level of the ocean does not stay the same all day long. Although stay the same all day long. Although waves continually wash the shore, the waves continually wash the shore, the actual water level changes as the day actual water level changes as the day passes. passes.

• It rises for a period It rises for a period of hours until it of hours until it reaches its highest reaches its highest level, and then it level, and then it begins to fall, or begins to fall, or recede, to its lowest recede, to its lowest level. This rise and level. This rise and fall of the ocean is fall of the ocean is known as the known as the tidetide. . 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.

High TideHigh Tide Low TideLow Tide

Tides – What are they?Tides – What are they?

• Tides are daily changes in the level Tides are daily changes in the level of ocean water.of ocean water.

• They are the periodic rise and fall of They are the periodic rise and fall of the water level in the oceans and the water level in the oceans and other large bodies of water.other 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?

What causes tides?What causes tides?

What moves ocean water?What moves ocean water?

• WindWind• EarthquakesEarthquakes• Plate tectonicsPlate tectonics• The dominant force that moves ocean The dominant force that moves ocean

water is the gravitational forces from water is the gravitational forces from both the both the sunsun and the and the moonmoon..

Early thoughts about what Early thoughts about what caused the tides.caused the tides.

• Some believed the earth was a Some believed the earth was a living animal and the tides a living animal and the tides a result of its breathing. result of its 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 caused by the beating of its great heart. great heart.

Early thoughts about what Early thoughts about what caused the tides.caused the tides.

• Early followers of the religious Early followers of the religious prophet Muhammad believed that the prophet Muhammad believed that the rise and fall of the waters were rise and fall of the waters were caused when the “Angel of the Sea” caused when the “Angel of the Sea” placed his foot in and out of the placed his foot in and out of the ocean. ocean.

• Primitive natives thought the tides Primitive natives thought the tides were a sign of a sea god’s anger and were a sign of a sea god’s anger and made human sacrifices to please him.made human sacrifices to please him.

The Lure of the MoonThe Lure of the Moon

• The relationship between the phases The relationship between the phases of the moon and the tides was of the moon and the tides was discovered more than 2,000 years discovered more than 2,000 years ago!ago!

• People of the time knew the moon People of the time knew the moon had something to do with the tides, had something to do with the tides, but they couldn’t explain why.but they couldn’t explain why.

Sir Isaac Newton to the Sir Isaac Newton to the Rescue!Rescue!

• Newton’s Newton’s Universal Universal GravitationGravitation theory helped to theory helped to explain how the explain how the gravity of the gravity of the moon (and the moon (and the sun) were related sun) were related to tides.to tides.

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 The moon’s gravitational pull on liquids is much more noticeable than liquids is much more noticeable than on solids.on solids.

• Why? Because liquids move more Why? Because liquids move more easily than solids.easily than solids.

What causes tides?What causes tides?

• How often tides occur and the How often tides occur and the difference in tidal levels depend on difference in tidal levels depend on the position of the moon as it the position of the moon as it revolves around the Earth.revolves around the Earth.

• The moon’s pull is strongest on the The moon’s pull is strongest on the part of the Earth directly facing the part of the Earth directly facing the moon.moon.

High TideHigh Tide

• The part of the ocean directly facing The part of the ocean directly facing the moon, bulges towards the moon.the moon, bulges towards the moon.

• There is a corresponding bulge on There is a corresponding bulge on the opposite side of the Earth.the opposite side of the Earth.

• These bulges are called These bulges are called high tide.high tide.

Low TideLow Tide

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

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 High tides happen on opposite sides of the Earth.of the Earth.

• The Earth rotates once on its axis The Earth rotates once on its axis every 24 hours.every 24 hours.

• How many high tides would any one How many high tides would any one place in the ocean experience each place in the ocean experience each day?day?

AnswerAnswer

• The periodic rise The periodic rise and fall of the and fall of the water level in the water level in the oceans and other oceans and other large bodies of large bodies of water happens . . .water happens . . .

• Twice each day!Twice each day!

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.

Tidal VariationsTidal Variations

• Tidal RangeTidal Range = the difference in levels = the difference in levels of ocean water at high tide and low of ocean water at high tide and low tide.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 Earthmoon 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.

Spring TideSpring 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 alignedmoon are aligned

Neap TidesNeap 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 third quarters of the moonthe moon

• The sun, Earth, and The sun, Earth, and moon form a 90 moon form a 90 degree angledegree angle

Weird Science!Weird Science!

• The moon also creates tides in our The moon also creates tides in our atmosphereatmosphere

• They are called They are called lunar windslunar winds

• They can be detected by studying They can be detected by studying slight periodic fluctuations in weather slight periodic fluctuations in weather patterspatters

• Very strange, indeed!Very strange, indeed!

ReviewReview

Q: Q: What are tides?What are tides?• TideTide = the periodic rise and fall of the = the periodic rise and fall of the

water level in the oceans and other large water level in the oceans and other large bodies of water.bodies of 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 sunsun and the and the moonmoon..

Review (cont’d)Review (cont’d)

Q: Q: Where is the moon’s pull is Where is the moon’s pull is strongest on the Earth?strongest on the Earth?

• The moon’s pull is strongest on the The moon’s pull is strongest on the part of the Earth directly facing the part of the Earth directly facing the moon.moon.

Review (cont’d)Review (cont’d)

Q: Q: Which one (the sun or the moon) Which one (the sun or the moon) has a bigger effect on tides?has a bigger effect on tides?

• The moonThe moon

Review (cont’d)Review (cont’d)

Q: Q: What is the difference in levels of What is the difference in levels of ocean water at high tide and low tide ocean water at high tide and low tide called?called?

• Tidal RangeTidal Range

Q: Q: Tidal ranges vary greatly due to the Tidal ranges vary greatly due to the combined forces of the _________ and combined forces of the _________ and the ________ on the Earththe ________ on the Earth

• Sun, moonSun, moon

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 situated in space so that we so that we experience a experience a spring tide?spring tide?

• Sun, Earth, and the Sun, Earth, and the moon are alignedmoon are aligned

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 that we experience a neap tide?a neap tide?

• The sun, Earth, and The sun, Earth, and moon form a 90 moon form a 90 degree angledegree angle