T IDES

G RAVITY  Remember, gravity is an invisible force of attraction between two objects.  What celestial object is attracted to the Earth?  The Moon  What celestial object is the Earth attracted to?  The Sun

E FFECT OF THE MOON ON THE E ARTH  The Moon’s gravity also pulls on the Earth. But because the Earth is so much larger than the moon, the Moon’s gravity doesn’t have much effect on the solid parts of the Earth.  However, the Earth is mostly covered with water. Water is a liquid and does respond to the pull of the Moon. This response creates tides.

S UMMARIZE : I N YOUR J OURNAL 1. The Earth is attracted to the _________. 2. The Moon is attracted to the _________. 3. This attraction is due to _____________. 4. What does the Moon’s gravity cause on Earth? 1. Sun 2. Earth 3. gravity 4. tides

T IDES  The how and why of tide formation is very complex.  This presentation will try to simplify how and why tides form.  To do this….

I MAGINE THAT THERE IS NOTHING BUT WATER COVERING THE E ARTH.

N OW, IMAGINE LOOKING AT THE E ARTH FROM ABOVE THE N ORTH P OLE. N

L ET ’ S ADD THE MOON TO THIS SYSTEM. N

T HE MOON PULLS ON THE WATER. This creates a bulge. N

B UT BECAUSE THE E ARTH IS SPINNING, THERE ARE ACTUALLY 2 BULGES CREATED. You’ll learn more about this in a course called Physics. N

T HIS BULGE OF WATER FOLLOWS THE MOON AS IT ORBITS THE E ARTH. N

I T TAKES THE MOON ABOUT 28 DAYS TO REVOLVE AROUND THE E ARTH. N

T HIS MAKES THE TIMES THAT THE TIDES OCCUR CHANGE IN A PREDICTABLE PATTERN.

B UT THERE IS MORE GOING ON THAN JUST THE REVOLUTION OF THE MOON AROUND THE E ARTH. The Earth rotates every day. N N

L ET ’ S PUT A PERSON ON THE EQUATOR OF THE E ARTH. Remember, you are looking at the Earth from the North Pole, so this person appears to be on the edge of the Earth. N

A S THE E ARTH ROTATES, THE PERSON WILL MOVE THROUGH TWO VERY HIGH BULGES OF WATER AND TWO AREAS OF LOW WATER EACH DAY. N

W E CALL THESE AREAS HIGH TIDE AND LOW TIDE. Remember, in a 24 hour period of rotation, there are two high tides and two low tides. N

This is what it looks like with both motions. N

S PRING T IDES  When the Sun, Earth, and Moon are in a straight line- the variation between high tide and low tide is greatest. This occurs during the full moon and new moon. High Tide N

S UMMARIZE : I N YOUR J OURNAL 5. Draw the positions of the Sun, Earth, and Moon during a spring tide:

N EAP T IDES  When the Sun, Earth, and Moon are in a perpendicular arrangement- the variation between high tide and low tide is not great. This occurs during the first and third quarter moon. High Tide N

S UMMARIZE : I N YOUR J OURNAL 5. Draw the positions of the Sun, Earth, and Moon during a neap tide: