Tides

1
Tides
2
Gravity

• Remember, that 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

3
Effect of the Moon on the Earth

• The Moons gravity pulls on the Earth.
• Since the Earth is essentially a solid and has a
  greater mass, it doesnt seem to respond to the
  gravitational pull.
• However, the Earth is mostly covered with water.
  Water is a liquid and does respond to the pull of
  the Moon. This response, among others, creates
  tides.

4
Tides

• The how and why of tide formation is quite
  complex.
• This presentation will try to simplify how tides
  form and why tides form.
• To do this.

5
Imagine that there is nothing but water covering
the Earth.
6
Now, imagine looking at the Earth from above the
North Pole.
N
7
Lets add the Moon to this system.
N
8
The Moon pulls on the water.
N
This creates a bulge.
9
But because the Earth is spinning there are
actually two bulges created.
N
10
This bulge of water follows the Moon as it orbits
the Earth.
N
11
It takes the Moon about 28 days to revolve around
the Earth.
N
12
This makes the times that the tides occur change
in a predictable pattern.
N
13
But, there is more going on than just the
revolution of the Moon around the Earth.
N
N
The Earth rotates every day.
14
Lets put a person on the equator of the Earth.
N
Remember, you are looking at the Earth from the
North Pole, so this person appears to be on the
edge of the Earth.
15
As the Earth rotates, the person will move
through two very high bulges of water and two
areas of low water each day.
N
16
We call these areas high tide and low tide.
N
Remember, in a 24 hour period of rotation, there
are two high tides and two low tides.
17
This is what it looks like with both motions.
N
18
That is a simplified version of how tides work.

• There are many things that complicate this cycle.
• Continents interfere with the movement of tides.
• The alignment of the Sun, Earth, and Moon
• What else would you like to know about tides?