1. Tides

2. Gravity
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

3. Effect of the moon on the Earth
The moon’s gravity also pulls on the Earth, but because the Earth is solid, it doesn’t seem to respond.
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.
The how and the why of tide formation is very complex.

4. Imagine that there is nothing but water covering the Earth.

5. Now imagine looking at the Earth from above the North Pole.

6. Let’s add the moon to this system.

7. The moon pulls on the water.
This creates a bulge like this.

8. But because the Earth is spinning there are actually 2 bulges created.

9. This bulge of water follows the moon as it orbits the Earth.

10. It takes the moon about 29.5 days to revolve around the Earth.

11. This makes the times that the tides occur change in a predictable pattern.

12. The Earth rotates every day.
But there is more going on than just the revolution of the moon around the Earth . N
The Earth rotates every day.

13. Let’s put a person on the equator of the Earth.
Remember you are looking at the Earth from the North Pole, so this person appears to be on the edge of the Earth.

14. As the Earth rotates, the person will move through two very high bulges of water and two areas of low water each day.
Low Tide

15. We call these areas high tide and low tide.
Remember in a 24 hour period of rotation, there are 2 high tides and 2 low tides.

16. This is what it looks like with both motions.

17. Spring Tides
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.
Tide
Low
High Tide
Sun

18. Neap Tides
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. This is called a Neap Tide.
Tide
Low
High Tide
Sun

19. High Tide vs. Low Tide
Click on the link below to see an example of high and low tides
Bay of Fundy, Canada