1. Natural Sciences Grade 7
Term 4: Planet Earth and Beyond
Relationship of the Moon to the Earth

2. Topic 2 Relationship of the Moon to the Earth
Tides
Natural Sciences - Grade 7

3. Natural Sciences - Grade 7
What are tides?
Tides are the repeated rise and fall of the sea and ocean levels.
It can be predicted.
The influence of the gravitational force between the Earth and the Moon, as well as the Sun, causes tides.
The coastlines show the influence very clearly and there are visible evidence.
Natural Sciences - Grade 7

4. Natural Sciences - Grade 7
High tide
The level of the sea rises higher against the seashore.
High tide is experienced when the Moon is directly overhead on the opposite side of the Earth.
It occurs every 12 hours and 25 minutes .
The highest tides occur when the Moon is new and full.
High tides sometimes occur either before or after the Moon is straight overhead.
Make sure that the learners notice the difference between low and high tide.
Ask them whether it is safe to swim during both tides. [They must motivate their answers with reasons]
Picture with movement [
In certain places the difference between high and low tides are very big, and in other places, the difference is drastic.
[movement of the moon]
Natural Sciences - Grade 7

5. Natural Sciences - Grade 7
Low tide
The tide is at its lowest level at a particular time and place.
Tides are about gravity.
The moon’s gravity causes tides.
The moon has enough gravity to move things around.
People can notice when the Moon’s gravity pulls on the ocean’s water.
Water, which is a liquid, can easily move around.
Natural Sciences - Grade 7

6. Two bulges during tides
While the water that is the closest to the Moon is getting pulled, the water that is the farthest from the Moon, is staying right where it is.
Both sides are experiencing gravity and inertia, but one side always overpowers the other.
The water bulges towards the Moon, and that bulge follows the Moon as the Earth turns beneath it.
Some places only have one high tide and one low tide in a cycle of 24 hours and 50 minutes.
On the side by the moon, gravity wins.
Inertia wins on the side away from the moon.
The two bulges are formed and it explains why there are two high tides and two low tides in one day.
[movement of the moon]
Natural Sciences - Grade 7

7. Natural Sciences - Grade 7
Spring tide
The Moon’s phase has an effect on the severity of the tides.
The Earth, Moon and Sun are aligned around the New Moon and Full Moon phases.
The Sun's gravitational pull adds to the Moon's gravity and it causes higher high tides and lower low tides. T
These tides are called spring tides.
The reason for a spring tide is that the Moon’s orbit lines up with the Sun.
It creates a large tidal range because it is extremely high or very low.
Scientists can predict when spring and neap tides will occur as well as each one’s height.
Factors that influence the tides:
- spinning motion of the Earth
- gravitational pulls of the moon and the Sun
- in a neap tide, the Sun and Moon are at the right angles to each other [balance each other out and it keeps the water level stable]. -
Natural Sciences - Grade 7

8. Natural Sciences - Grade 7
Neap tide
Neap tides occur during the first and third quarter phases of the Moon.
During these periods, the Sun and Moon are at 90° angles, and the gravity of the Sun cancels out a portion of the moon's gravitational pull.
Earth still experiences tides during these phases, because the Moon' s pull is stronger, but less extreme.
During neap tides the high tides are lower than the high tides during spring tides.
Neap tides are low tidal ranges between low and high tide.
The opposite of a neap tide is a spring tide.
Image of neap tide with movement [
Natural Sciences - Grade 7

9. Natural Sciences - Grade 7
Neap tide
The low neap tides are higher than the low spring tides.
Low tides are less extreme when the Moon and Sun are at right angles (the neap tides).
Neap tides are low tidal ranges between low and high tide.
The opposite of a neap tide is a spring tide.
Image of neap tide with movement [
Natural Sciences - Grade 7