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REET L2 · Social Studies

Motions of the Earth: Rotation, Revolution and Earthquakes

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This page explains the earth's two motions — rotation and revolution — their effects, the dates of the solstices and equinoxes, and the earthquakes and seismic waves produced by the earth's internal movement, briefly and for the exam. REET 2024 carried 5 questions on this topic, asking straight facts like the axis's angle, the epicentre, the L wave, and the earth's density.

  • 5 questions in REET 2024
  • Class 6–8 & NCERT level
  • 7 min read
Verified 17 September 2026 · Source: NCERT Class 11 Fundamentals of Physical Geography, Chapter 3: Interior of the Earth

How REET asks about this topic

Of REET 2024's 5 questions, one was directly on the earth's motion — the angle the axis makes with the orbital plane (66½°, not 23½°). Two were on earthquakes — the point directly above the focus on the surface (the epicentre) and the most destructive wave (the L/surface wave). The remaining two were on general facts about the solar system and the earth — the earth's density (5.5) and a 'false statement' involving inner and outer planets. So this topic mixes the earth's motions with its internal movement (earthquakes) and basic solar-system facts; precision in numbers and terms matters most here.

Rotation and revolution — key facts

Rotation
The earth spinning on its own axis; from west to east; one turn takes about 24 hours — also called the daily motion.[Source 2]
Effect of rotation
Causes day and night; the sun appears to rise in the east and set in the west.
Circle of Illumination
The imaginary circle that divides day from night; it does not coincide with the axis.[Source 2]
Revolution
Moving around the sun in an elliptical orbit; one turn takes 365¼ days — the annual motion.[Source 2]
Leap year
The extra ¼ day left over each year adds up to one full day every four years, which is added in February (making it 29 days); a leap year has 366 days.[Source 2]
Axial tilt
The axis makes an angle of 66½° with the orbital plane; put another way, it is tilted 23½° from the perpendicular to the orbital plane.[Source 2]
Effect of revolution
Change of seasons and difference in day-night length (because of revolution combined with the tilted axis).
Shape of the earth
Slightly flattened at the poles and bulging at the equator — this shape is called a 'geoid'.
Inner and outer planets
Inner (terrestrial) planets: Mercury, Venus, Earth, Mars; outer (Jovian) planets: Jupiter, Saturn, Uranus, Neptune.
Earth's average density
About 5.5 grams per cubic cm — the highest among the planets of the solar system.

Solstices and equinoxes

DatePositionSun's direct raysEffect
21 JuneSummer Solstice (Northern hemisphere)On the Tropic of Cancer (23½° N)Longest day and shortest night in the Northern hemisphere; summer there, winter in the Southern hemisphere
22 DecemberWinter Solstice (Northern hemisphere)On the Tropic of Capricorn (23½° S)Longest day in the Southern hemisphere; summer in Australia (a warm Christmas)
21 MarchEquinox — Spring/Vernal Equinox (for the Northern hemisphere)On the EquatorDay and night are equal everywhere on earth
23 SeptemberEquinox — Autumnal Equinox (for the Northern hemisphere)On the EquatorDay and night are equal everywhere on earth

Remember: the day-night difference is greatest at the solstices and zero at the equinoxes.[Source 2]

The earth's internal movement: earthquakes

Besides rotation and revolution, there's constant movement inside the earth too. The motion of lithospheric plates releases energy suddenly, and the ground shakes — this is called an earthquake. The point inside the earth where the energy is released is called the focus, or hypocentre. The point on the surface directly above the focus, nearest to it, is called the epicentre — waves reach here first. Earthquakes are recorded with a seismograph.

Seismic waves are of two kinds — body waves and surface waves. Body waves travel from the focus in all directions; on reaching the surface, they generate surface waves. The zone at an angular distance of 105° to 145°, where no seismic wave is recorded, is called the shadow zone — both P and S waves are recorded up to 105°, while beyond 145° only P waves are recorded. That S waves cannot pass through the outer core tells us the outer core is liquid.

Comparing seismic waves

WaveSpeed / order of arrivalMedium it travels throughFeature
P wave (Primary)Fastest; arrives firstSolids, liquids and gases — all threeLike sound waves; longitudinal
S wave (Secondary)Arrives after P, with some gapSolids onlyTransverse; cannot travel through the liquid outer core
L / Surface waveArrives lastTravels along the surfaceThe most destructive — displaces rock and brings down buildings

[Source 1]

How to teach this to children

Classroom activity (Class 6)

In a dark room, demonstrate with a torch (the sun) and a globe on a tilted axis: spin the globe to show day and night and the circle of illumination; then, keeping the tilt fixed, move it around the torch to the four positions (21 June, 23 September, 22 December, 21 March) to show where the rays fall directly.

Teaching materials

A globe, a torch, a protractor-made card model showing angles of 66½° and 23½°; a slinky spring for earthquakes — pushing it back and forth for a P wave, and shaking it up and down for an S wave.

Common misconceptions

The most common one: 'It's summer because the earth is closer to the sun then.' Seasons are mainly caused by the tilted axis changing the angle of the rays and the length of the day — proof of this is that both hemispheres have opposite seasons at the same time. A second misconception: 'the epicentre is inside the earth' — that's the focus.

Assessment approach

Picture-based questions: give a four-position revolution diagram and have students write the date and the hemisphere's season; ask 'why' questions — 'why is it summer in Australia in December?'

Memory trick / exam tip

For angle questions, watch the wording: 'angle with the orbital plane' = 66½°, 'tilt from the vertical/perpendicular' = 23½° — the two add up to 90°. For waves: 'P = first, passes through everything; S = solid only; L = last and most destructive'.

Questions asked in REET 2024 (solved)

Question 102

What is the angle between the axis of the earth and its orbital plane ?

  1. A23½°
  2. B66½°
  3. C90°
  4. D85°

Explanation

पृथ्वी का अक्ष अपनी कक्षा के तल के लम्ब (ऊर्ध्वाधर) से 23½° झुका हुआ है। इसलिए अक्ष और कक्षीय तल के बीच का कोण 90° − 23½° = 66½° होता है। 23½° वाला विकल्प लम्ब से झुकाव है, कक्षीय तल से कोण नहीं।

Question 106

The nearest point on earth surface from focus, is known as

  1. Aअवकेन्द्र
  2. Bछाया क्षेत्र
  3. Cविवर्तनिक केन्द्र
  4. Dअधिकेन्द्र

Explanation

भूकम्प जिस स्थान पर पृथ्वी के भीतर उत्पन्न होता है उसे भूकम्प मूल (focus/hypocentre) कहते हैं। पृथ्वी की सतह पर भूकम्प मूल के ठीक ऊपर स्थित निकटतम बिन्दु को अधिकेन्द्र (epicentre) कहते हैं, जहाँ भूकम्पीय तरंगें सबसे पहले पहुँचती हैं। अवकेन्द्र तो स्वयं भूकम्प मूल है, इसलिए (A) गलत है।

Question 141

Which of the following statements is not correct ?

  1. Aअर्सा मेजर या बिग बीयर एक नक्षत्रमंडल है ।
  2. Bबड़े आकार वाले गर्म खगोलीय पिंड जो गैसों से बने होते हैं, स्वयं की ऊर्जा व प्रकाश रखते हैं, वे तारे कहलाते हैं ।
  3. Cबृहस्पति, शनि, यूरेनस, नेप्च्यून आंतरिक ग्रह हैं ।
  4. Dपृथ्वी के आकार को ‘भू आम’ कहा जाता है ।

Explanation

बृहस्पति, शनि, यूरेनस और नेप्च्यून बाहरी ग्रह (outer/Jovian planets) हैं; आंतरिक ग्रह बुध, शुक्र, पृथ्वी और मंगल हैं। इसलिए कथन (C) सत्य नहीं है। अर्सा मेजर (सप्तर्षि/बिग बीयर) एक नक्षत्रमंडल है, तारे स्वयं प्रकाश और ऊष्मा वाले गैसीय पिंड हैं और पृथ्वी की आकृति को 'जियोइड' (भू-आभ) कहा जाता है।

Question 131

The density of earth is

  1. A4.5
  2. B5.5
  3. C6.5
  4. D7.5

Explanation

पृथ्वी का औसत घनत्व लगभग 5.5 ग्राम प्रति घन सेमी (5.51 g/cm³) है। भूपर्पटी (crust) का घनत्व लगभग 2.7–3.0 होता है, जबकि केन्द्रीय क्रोड (core) का घनत्व बहुत अधिक (लगभग 10–13) होता है, जिससे औसत घनत्व 5.5 आता है।

Question 148

The most destructive earthquake wave is

  1. Aपी तरंग
  2. Bएस तरंग
  3. Cएल तरंग
  4. Dपी* तरंग

Explanation

भूकंप की L तरंगें (धरातलीय/सतही तरंगें, Love व Rayleigh) सबसे अधिक विनाशकारी होती हैं, क्योंकि ये पृथ्वी की सतह पर चलती हैं और चट्टानों व इमारतों में सबसे अधिक विस्थापन पैदा करती हैं। P तरंगें सबसे तेज़ चलती हैं और सबसे पहले पहुँचती हैं, जबकि S तरंगें केवल ठोस माध्यम से गुजरती हैं; ये दोनों भूगर्भीय (body) तरंगें हैं।

Practice questions

Question 1

In which direction does the Earth rotate on its axis?

  1. Aपूर्व से पश्चिम
  2. Bपश्चिम से पूर्व
  3. Cउत्तर से दक्षिण
  4. Dदक्षिण से उत्तर

Explanation

The earth rotates from west to east, which is why the sun appears to rise in the east and set in the west.

Question 2

On 21 June, the Sun's rays fall vertically on which line?

  1. Aभूमध्य रेखा
  2. Bमकर रेखा
  3. Cकर्क रेखा
  4. Dआर्कटिक वृत्त

Explanation

On 21 June (summer solstice), the Northern hemisphere is tilted toward the sun, and its rays fall directly on the Tropic of Cancer. They fall on the Tropic of Capricorn on 22 December, and on the Equator at the equinoxes.

Question 3

On which date are day and night equal all over the Earth?

  1. A21 जून
  2. B23 सितंबर
  3. C22 दिसंबर
  4. D4 जुलाई

Explanation

23 September and 21 March are equinoxes, when the sun's rays fall directly on the equator and neither pole is tilted toward the sun. 21 June and 22 December are solstices.

Question 4

Which seismic wave can travel only through solid materials?

  1. AP तरंग
  2. BS तरंग
  3. CL तरंग
  4. Dउपर्युक्त सभी

Explanation

Per NCERT, S waves travel only through solids, while P waves travel through solids, liquids and gases. L waves travel along the surface.

Question 5

The seismic shadow zone lies between which angular distances from the epicentre?

  1. A0° और 105°
  2. B105° और 145°
  3. C145° और 180°
  4. D90° और 120°

Explanation

Both P and S waves are recorded up to 105°, and beyond 145° only P waves are recorded. No wave is recorded between 105° and 145°, which is why it's called the shadow zone.

Question 6

The main reason for summer in Australia in December is—

  1. Aपृथ्वी का घूर्णन
  2. Bदिसंबर में दक्षिणी गोलार्ध का सूर्य की ओर झुका होना
  3. Cदिसंबर में पृथ्वी का सूर्य से सबसे दूर होना
  4. Dऑस्ट्रेलिया का भूमध्य रेखा पर स्थित होना

Explanation

Around 22 December, the Southern hemisphere is tilted toward the sun, so rays fall more directly there and days are longer. Seasons are caused by the axial tilt, not distance — and Australia isn't on the equator either.

Question 7

How many days does February have in a leap year?

  1. A28
  2. B29
  3. C30
  4. D31

Explanation

Revolution takes 365¼ days; the leftover ¼ day each year adds up to one full day every four years, added to February to make it 29 days.

Question 8

Which of the following statements is correct?

  1. Aअधिकेन्द्र पृथ्वी के भीतर स्थित होता है
  2. Bभूकंप मूल को अवकेन्द्र भी कहते हैं
  3. CS तरंगें सबसे पहले पहुँचती हैं
  4. Dधरातलीय तरंगें सबसे कम विनाशकारी होती हैं

Explanation

The focus is also called the hypocentre. The epicentre is on the surface, P waves arrive first, and surface waves are the most destructive.

Question 9

The most suitable teaching strategy to explain day and night formation in Class 6 is—

  1. Aपरिभाषा श्यामपट्ट पर लिखकर याद कराना
  2. Bअंधेरे कमरे में टॉर्च और ग्लोब से घूर्णन का प्रदर्शन
  3. Cकेवल पाठ्यपुस्तक का सस्वर वाचन
  4. Dगृहकार्य में प्रश्नोत्तर लिखवाना

Explanation

Rotation is an abstract process; the torch-globe demonstration makes it concrete and visible, so children see for themselves that it's day on the lit side and night on the other. The other options rely on rote learning.

Question 10

A student says, 'Summer happens because the Earth is closest to the Sun then.' Which fact can the teacher use most effectively to correct this misconception?

  1. Aपृथ्वी की कक्षा दीर्घवृत्ताकार है
  2. Bएक ही समय उत्तरी और दक्षिणी गोलार्ध में विपरीत ऋतुएँ होती हैं
  3. Cपृथ्वी 24 घंटे में घूर्णन करती है
  4. Dपृथ्वी का घनत्व 5.5 है

Explanation

If distance caused the seasons, both hemispheres would have the same season at the same time. Opposite seasons show the cause is the axial tilt. The elliptical-orbit fact could actually reinforce the misconception.

Frequently asked questions

What angle does the earth's axis make with the orbital plane?+

66½°. The axis is tilted 23½° from the perpendicular to the orbital plane, so the angle with the orbital plane itself is 90° − 23½° = 66½°.

What's the difference between rotation and revolution?+

Rotation is the earth spinning on its own axis in about 24 hours, which causes day and night. Revolution is going around the sun in 365¼ days, which (with the tilted axis) changes the seasons.

What's the difference between focus and epicentre?+

The focus (hypocentre) is the point inside the earth where energy is released; the epicentre is the nearest point on the surface, directly above it.

Which seismic wave is the most destructive?+

The surface waves (L waves). They arrive last, but because they travel along the surface, they displace rock and bring down buildings.

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REET Syllabus

The complete official syllabus for every subject

REET 2024 Solved Paper

Questions from every shift, official answers and explanations

Official Sources

  1. NCERT Class 11 Fundamentals of Physical Geography, Chapter 3: Interior of the Earth
  2. NCERT Class 7 Science (Curiosity) — Chapter 12: Earth, Moon, and the Sun

Change Log

  • 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked