Tides and Their Causes
Delhi Police & SSC Exams
1. Introduction
Tides are the periodic rise and fall of sea level caused mainly by the gravitational attraction of the Moon and the Sun on Earth's oceans.
They occur regularly twice a day and play a vital role in navigation, fishing, and coastal formation.
Key Concepts:
- Gravitational forces and tide formation
- Spring and neap tides
- Moon phases and tidal patterns
- Practical applications of tides
Exam Focus:
Causes of tides
Spring vs neap tides
Tide importance and applications
2. What Are Tides?
Definition:
Tides are the alternating rise and fall of ocean water on the coasts due to the combined gravitational pull of the Moon and the Sun and the rotation of the Earth.
Key Terms:
| Term | Meaning |
|---|---|
| High Tide | Sea level rises and water covers more of the shore. |
| Low Tide | Sea level falls and water recedes from the shore. |
3. Causes of Tides
| Cause | Explanation |
|---|---|
| Gravitational Force of Moon | The Moon exerts a strong pull on Earth's oceans → water bulges toward the Moon (high tide). |
| Gravitational Force of Sun | The Sun also affects tides, though less strongly (because of its greater distance). |
| Centrifugal Force | Due to Earth's rotation, a bulge occurs on the opposite side of the Earth, creating another high tide. |
4. Types of Tides
| Type | Description |
|---|---|
| Spring Tides | When the Sun, Moon, and Earth are in a straight line (New Moon and Full Moon) → highest high tides. |
| Neap Tides | When the Sun and Moon form a right angle with Earth (First and Third Quarter) → lowest high tides. |
| Daily Tides | Two high and two low tides occur in about 24 hours (semi-diurnal type). |
5. Phases of the Moon and Tides
| Moon Phase | Tide Type | Alignment |
|---|---|---|
| New Moon | Spring Tide | Sun–Moon–Earth in one line |
| Full Moon | Spring Tide | Earth between Sun and Moon |
| First Quarter | Neap Tide | 90° angle between Sun and Moon |
| Third Quarter | Neap Tide | 90° angle again |
6. Tide Formation Diagrams
Spring Tide (Full Moon / New Moon)
Sun
Moon
Earth
High Tide on both sides
Neap Tide (Quarter Phases)
Sun
Moon
Earth
Low Tides
7. Importance of Tides
| Aspect | Importance |
|---|---|
| Navigation | Ships enter and leave ports easily during high tide. |
| Fishing | Helps in catching fish (fish come to surface during tides). |
| Tidal Energy | Used for generating renewable electricity. |
| Coastal Formation | Helps in sediment transport and shaping coasts. |
8. Memory Tricks
SPRING = Strong
Highest Tide
NEAP = Not Deep
Lowest Tide
Moon's Pull
Main Cause
Previous Year Questions (PYQs)
The primary cause of tides on Earth is –
Options: A) Wind blowing across oceans B) Earth's rotation C) Gravitational pull of the Moon and the Sun D) Ocean currents
Category: Causes
Show Answer
C) Gravitational pull of the Moon and the Sun
The highest tides in the sea occur at –
Options: A) New Moon and Full Moon B) First Quarter C) Third Quarter D) Half Moon
Category: Tide Types
Show Answer
A) New Moon and Full Moon
Spring tides occur when –
Options: A) Sun, Moon, and Earth are in one line B) Sun and Moon are at right angles C) The Moon is farthest from Earth D) During an eclipse only
Category: Spring Tides
Show Answer
A) Sun, Moon, and Earth are in one line
Neap tides occur when the Moon is in –
Options: A) New Moon position B) Full Moon position C) First or Third Quarter D) Perigee position
Category: Neap Tides
Show Answer
C) First or Third Quarter
Which of the following helps ships to enter harbours easily?
Options: A) Ocean currents B) High tide C) Low tide D) Monsoon winds
Category: Practical Applications
Show Answer
B) High tide
Tidal energy is generated mainly during –
Options: A) High tide only B) Low tide only C) Rise and fall of tides D) Neap tides
Category: Energy Generation
Show Answer
C) Rise and fall of tides
10. Comparison Table: Spring vs Neap Tides
| Feature | Spring Tide | Neap Tide |
|---|---|---|
| Alignment | Sun, Moon, Earth in one line | Sun and Moon at right angles |
| Occurs | Full Moon, New Moon | First and Third Quarter |
| Tide Height | Highest | Lowest |
| Gravitational Pull | Combined (Strong) | Opposing (Weak) |
| Frequency | Twice a month | Twice a month |
Final Exam Tips
Moon's gravity > Sun's gravity (because it's closer)
2 high + 2 low tides in 24 hours = Semi-diurnal type (most common)
Spring → Strongest tides (Full/New Moon)
Neap → Weakest tides (Quarter phases)
Tidal energy is a renewable resource – example: Gulf of Khambhat (India)
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