Name: ___________________________
Period: _____
Which Tide Is Which?
Background Information:
Tides are due to the gravity of the Moon trying to pull the part of the sea closest to it towards it. Tides are the
regular rising and falling of the sea. You have seen this if you have been to the ocean. There are about two
high tides and two low tides a day. This cycle of high tide to low tide to high tide occurs approximately every
12.5 hours.
The Sun also has a gravitational effect on the sea. Although the Sun is larger than the Moon, it is further away
from the Earth, which means that it has less effect on our tides. Different locations of the sun, moon, and Earth
in relationship to each other result in different kinds of tides.
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At a new or full moon, the sun and moon will be pulling in the same direction or in exactly opposite
directions and will produce strong tides known as spring tides.
The much lower neap tides occur when the moon is at first or third quarter positions as the
gravitational pull works against that of the sun.
The centrifugal force produced as the Earth revolves around the sun tends to project force in the opposite
direction of the moon’s gravitational pull. This will strengthen the second high tide which occurs on the side
away from the moon
Diagrams:
In the diagram below, there will be a high tide at point A. There will also be a high tide on the opposite side of
the Earth at point C. At points B and D there will be a low tide.
The Earth rotates once every 24 hours which means that the places on the Earth where HIGH and LOW occur
tides are always changing. The diagram below shows where HIGH and LOW tides will be 6 hours after the
diagram above.
Science 8- Seasons, Moon Phases, and Tides
Twice a month, during the new moon and the full moon, the Moon and the Sun are in line with the Earth and
so they pull together. This causes very high high tides and very low low tides called SPRING tides.
Twice a month, during the first and third (or last) quarters, the Sun and Moon are at right angles to each
other, and so their pulls sort of cancel each other out, and are not as great. This causes much smaller tides.
These are called NEAP tides.
Questions:
1. If it is LOW tide at a harbor at 9:00 am, at about what time would you expect it to be HIGH tide in the
afternoon?
2. If it is HIGH tide at 8:00 pm, when would you expect the next HIGH tide to be?
3. The two diagrams to the right show the position of the
Sun, Moon and Earth. Circle which would produce the
HIGHEST tides? Explain reasons for your answer
below.
Science 8- Seasons, Moon Phases, and Tides
Draw the appropriate tidal bulge for both spring and neap tides. Label the diagram as either spring tide or neap
tide. On the lines provided, explain the position of the sun, moon, and Earth and include the moon phase.
4. __________________
5. __________________
6. __________________
7. __________________
Science 8- Seasons, Moon Phases, and Tides
8. What objects are high tides always associated with?
a. Sun
b. Earth
c. Moon
d. Gravity
9. Why does the sun, which is larger, have less effect on the tides than the moon does?
10. Describe what causes spring tides.
11. Describe what causes neap tides.
12. How much time passes between one high tide and the next high tide?
13. How much times passes between one high tide and the next low tide?
Science 8- Seasons, Moon Phases, and Tides