Authentic Classroom Explanation by IAS Monk

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📍 The Question

With reference to the Coriolis force, which of the following statements is/are correct?

1. It increases with increase in wind velocity.
2. It is maximum at the poles and is absent at the equator.

Select the correct answer using the code given below:

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer: (c) Both 1 and 2

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🎯 Theme of the Question

Physical Geography | Climatology | Wind Systems | Earth’s Rotation

This is a core conceptual question testing understanding of how Earth’s rotation influences wind direction.

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🧠 Classroom Explanation

Let us examine each statement carefully.

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🔹 Statement 1: Coriolis force increases with increase in wind velocity. ✅

• Coriolis force depends on:
  • Speed of the moving air
  • Latitude
  • Earth’s rotation
• Faster winds experience greater deflection
• Slow-moving air shows minimal Coriolis effect

✔️ Statement 1 is correct

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🔹 Statement 2: Coriolis force is maximum at the poles and absent at the equator. ✅

• Coriolis force is directly proportional to latitude
• At the equator (0°):
  • Deflective force = zero
• Towards the poles (90°):
  • Deflection reaches maximum

✔️ Statement 2 is correct

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📊 Final Assessment

Statement	Status
Increases with wind speed	✅ Correct
Maximum at poles, zero at equator	✅ Correct

👉 Correct answer: (c)

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🧠 Now, let us EXPLAIN THE IMAGE (very important)

The diagram you uploaded shows three key ideas simultaneously. I’ll decode it layer by layer.

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🔁 1. Earth’s Rotation → Coriolis Force

• Earth rotates west to east
• Any freely moving object (wind, ocean current) appears to deflect due to this rotation
• This apparent deflection is called Coriolis force

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🌍 2. Direction of Deflection (Shown by Arrows)

Northern Hemisphere

• Winds deflect to the RIGHT of their path

Southern Hemisphere

• Winds deflect to the LEFT of their path

This is clearly shown in the diagram with curved arrows.

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📍 3. Latitude-wise Variation (Percentages in the diagram)

• 0% at the Equator (0°)
  → No Coriolis force
  → Winds move straight, perpendicular to isobars
• Increasing effect at 30°, 60°
  → Deflection increases with latitude
• 100% at the Poles (90°)
  → Maximum Coriolis force
  → Strongest deflection

This explains the “Maximum at pole” label in the image.

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🧭 4. Interaction with Pressure Gradient Force

• Pressure Gradient Force (PGF):
  • Pushes air from high pressure to low pressure
  • Acts perpendicular to isobars
• Coriolis Force:
  • Acts perpendicular to wind direction

Together, they cause:

• Winds to circulate around pressure systems
• Instead of moving straight into low pressure

This is why:

• Winds spiral around cyclones
• Anticyclones rotate in opposite directions in each hemisphere

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🌪️ 5. Why Cyclones Do NOT Form at the Equator

From the diagram:

• At the equator → Coriolis force = 0
• Winds move straight into low pressure
• Low pressure gets filled, not intensified

👉 Hence:

Tropical cyclones do not form near the equator

This is a very common UPSC linkage.

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🧩 Memory Hooks (Exam Gold)

• “Fast wind → more bend”
• “No Coriolis, no cyclone”
• Right in North, Left in South”

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🧠 Prelims Strategy Insight

For Coriolis-based questions, always check:

1. Wind speed
2. Latitude
3. Hemisphere
4. Interaction with pressure gradient

If all four align → answer is clear.

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🧭 IAS Monk Whisper

The wind thinks it moves straight — Earth gently proves it wrong.