Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

Unit 3: The Solar System and energy

Tides — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 9 parts Lesson 9 of 14 2 quizzes

📚 HIA International - Grade 6 Hub / Topical Revision
🩺
100% Curriculum Specification Match Lesson Doctor Verified
The only platform with 100% curriculum specification match and verified interactive question banks.
0%read
Lesson summary

3.4 Tides — HIA INTERNATIONAL notes: Explain what tides are, how the gravity of the Moon and Sun causes them, and what effects they have.Tide — the regular change in the depth of the ocean at a place, where depth is the distance from the water surface to the bottomHigh tide and l…

  • High tide and low tide
  • Tidal range
  • Earth tide
  • High tides
  • High tide to the next low tide
  • Moon's gravity

Part 1 of 7What a tide is

Tide
  • Tide the regular change in the depth of the ocean at a place, where depth is the distance from the water surface to the bottom
High tide and low tide
  • High tide and low tide the highest and lowest water depths in the cycle, about six hours apart
Tidal range
  • Tidal range the difference in depth of the water between high tide and low tide
  • The largest tidal range in the world is 16.3 m, in the Bay of Fundy in Canada.
  • Some of the smallest tidal ranges are found in the Caribbean and Mediterranean seas.
Earth tide
  • Earth tide the land also rises and falls through the day, with a tidal range of about 30 cm

Part 2 of 7Timing of the tides

Timing of the tides
High tides
  • High tides about 12 hours apart
Low tides
  • Low tides also about 12 hours apart
High tide to the next low tide
  • High tide to the next low tide about 6 hours

Part 3 of 7Cause of tides: the Moon

Moon's gravity
  • Moon's gravity the Moon orbits the Earth and its gravity pulls on the Earth as well as the Earth pulling on it
Tidal force
  • Tidal force the pull of the Moon's gravity that causes tides
  • The Moon's gravity pulls the water in the oceans more easily than the land.
Near side
  • Near side the side of the Earth closest to the Moon has a high tide
Far side
  • Far side the side furthest from the Moon also has a high tide

Part 4 of 7Why there are two high tides a day

1
The Earth spins once on its axis in 24 hours.
2
A place on the side closest to the Moon has a high tide.
3
12 hours later the same place is on the far side of the Earth, which also has a high tide.
4
So high tides are about 12 hours apart, giving two high tides and two low tides every day.

Part 5 of 7Cause of larger tides: the Sun

Sun's tidal force
  • Sun's tidal force the Sun also produces a tidal force on the Earth, but it is weaker because the Sun is further away than the Moon
Alignment
  • Alignment when the Earth, Moon and Sun are in a line the two forces combine and the tidal range is greater
  • This happens at full Moon and at new Moon.
  • The highest tides therefore occur twice in each lunar month.

Part 6 of 7Effects of tides

Harbours
  • Harbours some harbours can only be used at certain times because boats cannot move safely if the water is not deep enough
Flooding
  • Flooding coastal areas are more likely to flood at high tide when winds are strong
Water flow
  • Water flow the flow of water in and out of some coastal areas is dangerous for small boats
Food chains
  • Food chains at low tide birds can eat shellfish that are no longer covered by water, and some fish move to find food with the tides
Earth tides
  • Earth tides volcano eruptions and earthquakes have been linked with earth tides, so studying them may help predict dangerous volcanoes
Electricity
  • Electricity the movement of tidal water can be used to generate electricity

Part 7 of 7How the cause of tides was discovered

330 BCE
  • 330 BCE a Greek sailor observed that water depth rose to a maximum twice every day and thought the Moon was the cause,
  • but he could not explain it without knowledge of gravity
About 1600
  • About 1600 a German scientist suggested a force of attraction between the Moon and water, wrongly proposing that it was magnetic
1687
  • Newton used his ideas about gravity to calculate the tidal forces,
    • and his accurate predictions showed that gravity from the Moon and Sun causes the tides

Key terms

TermMeaning
TideThe regular change in the depth of the ocean at a place.
Tidal forceThe pull of gravity from the Moon (and Sun) that causes tides.
Tidal rangeThe difference in water depth between high tide and low tide.
Earth tideThe rise and fall in the height of the land through the day.
High tideThe time when the water is deepest.
Low tideThe time when the water is shallowest.

Avoid these mistakes

1
Saying the Sun is the main cause of tides — the Moon is closer, so its tidal force is the stronger one
2
Saying there is only one high tide a day — the far side of the Earth also has a high tide, giving two a day
3
Saying the tidal force is magnetic — it is the force of gravity
4
Confusing tidal range with depth — tidal range is the difference in depth between high and low tide

Last updated: