Gravitation Notes for NEET and JEE Main 2027: Key Points and PDF

Gravitation is Chapter 7 of NCERT Class 11 Physics and Unit 6 in both the NEET UG and JEE Main syllabi. These notes cover Kepler’s laws, the universal law of gravitation, the gravitational constant, variation of g with height and depth, gravitational potential energy, escape speed, earth satellites and their energy, with a free PDF.

Gravitation Notes for NEET and JEE Main

Section-wise key points from NCERT Chapter 7, formula tables, high-yield facts and common mistakes for 2027 revision.

Gravitation at a Glance

Topics follow the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and the JEE Main 2026 syllabus published by NTA. Both stay the reference until the 2027 syllabi are out. Full lists: NEET syllabus and JEE Main syllabus.

Kepler’s Laws of Planetary Motion

Johannes Kepler (1571-1630) extracted three laws from the naked-eye planetary data recorded by Tycho Brahe (1546-1601).

• The law of areas holds for any central force, not only the inverse-square law of gravitation.
• The semi-major axis is half the distance between perihelion and aphelion; for a circle it is the radius.

Universal Law of Gravitation and the Constant G

Every body attracts every other body with a force F = Gm₁m₂/r², directed along the line joining them.

• Forces from several masses add as vectors (principle of superposition).
• A uniform spherical shell attracts a point mass outside it as if the whole mass were at its centre.
• A uniform spherical shell exerts zero force on a point mass inside it.
• Henry Cavendish first measured G in 1798, using a torsion balance with small and large lead spheres.
• Accepted value: G = 6.67 × 10⁻¹¹ N m² kg⁻².
• Knowing G, g and R_E gives the mass of the earth, M_E = gR_E²/G, so ‘Cavendish weighed the earth’.

Acceleration Due to Gravity and Its Variation

At the earth’s surface g = GM_E/R_E². The value falls both above and below the surface.

• Below the surface, only the inner sphere of radius (R_E − d) pulls the body; the outer shell exerts no force.
• The depth result assumes the earth has uniform density.

Gravitational Potential Energy and Gravitational Potential

Gravitational potential energy of two masses r apart is V = −Gm₁m₂/r, taking the zero of potential energy at infinity.

• Only differences in potential energy have physical meaning; the choice of zero does not change the force.
• With zero at infinity, gravitational potential energy is always negative.
• For a mass m at distance r (> R_E) from the earth’s centre: W(r) = −GM_Em/r.
• Gravitational potential is the potential energy per unit mass at a point.
• mgh is an approximation to the difference in gravitational potential energy close to the earth’s surface.
• For a system of particles, total potential energy is the sum over all pairs (superposition).

Escape Speed

Escape speed is the minimum speed with which a body must be projected so that it reaches infinity and does not return.

• From energy conservation: ½mv² ≥ GM_Em/(h + R_E).
• From the surface: v_e = √(2GM_E/R_E) = √(2gR_E) ≈ 11.2 km/s. It does not depend on the mass of the body.
• On the moon the escape speed is about 2.3 km/s, about five times smaller, which is why the moon has no atmosphere.

Earth Satellites: Orbital Speed and Period

For a satellite in a circular orbit of radius (R_E + h), gravity supplies the centripetal force.

• The moon is the earth’s only natural satellite, with a period of about 27.3 days, roughly equal to its rotation period about its own axis.
• Kepler’s third law also holds for elliptical orbits if (R_E + h) is replaced by the semi-major axis.
• Weightlessness in a satellite is not due to weak gravity there: the astronaut and the satellite are both in free fall towards the earth.

Energy of an Orbiting Satellite

The total energy of a satellite in a circular orbit is negative, which is why it stays bound to the earth.

• In an elliptical orbit, K and U change from point to point but the total energy stays constant and negative.
• If the total energy were zero or positive, the body would escape to infinity.
• Energy needed to send an orbiting satellite out of the earth’s influence equals the magnitude of its total energy, GM_Em/2(R_E + h).

Most-asked Facts for NEET and JEE Main: Gravitation

Revise these one-line facts from the NCERT chapter just before the exam.

• G = 6.67 × 10⁻¹¹ N m² kg⁻², first measured by Cavendish (1798).
• Kepler’s law of areas is a consequence of conservation of angular momentum under a central force.
• T² ∝ a³ for all planets around the Sun.
• Under gravity, angular momentum and total mechanical energy are conserved; linear momentum is not.
• Force on a mass inside a uniform spherical shell is zero; gravitational shielding is not possible.
• g(h) ≈ g(1 − 2h/R_E) for small h; g(d) = g(1 − d/R_E).
• g is zero at the centre of the earth.
• Escape speed from the earth ≈ 11.2 km/s; from the moon ≈ 2.3 km/s.
• Orbital speed decreases as the orbit radius increases.
• Near-surface satellite period ≈ 85 minutes.
• Satellite energy: K = −E, U = 2E, and E is negative.
• Weightlessness in orbit is due to free fall, not absence of gravity.

Common Mistakes to Avoid

Watch for these mix-ups when you answer questions on this chapter.

• Using g(h) ≈ g(1 − 2h/R_E) for large heights. It holds only when h is much smaller than R_E; otherwise use GM_E/(R_E + h)².
• Saying g increases below the surface. It decreases linearly with depth and is zero at the centre.
• Taking gravitational potential energy as positive. With zero at infinity it is always negative.
• Thinking escape speed depends on the mass of the projectile. It depends only on the planet’s mass and radius.
• Assuming a higher satellite moves faster. Orbital speed falls with height while the period increases.
• Writing the satellite’s total energy as positive or equal to K + |U|. It is K + U = −GM_Em/2(R_E + h).
• Explaining weightlessness by zero gravity at the orbit. Gravity there is only somewhat weaker; the cause is free fall.
• Measuring orbit radius from the surface. Use (R_E + h) from the earth’s centre in every formula.

Gravitation Notes PDF and Related Pages

Download the AglaSem notes for Gravitation (key notes on Newton’s law of gravitation, variation of g, potential, escape and orbital velocity and satellites, with important questions and answers) free: View PDF

• All chapters: NEET and JEE Main Physics notes
• Full topic lists: NEET syllabus and JEE Main syllabus
• Practice: NEET question papers and JEE Main question papers
• Source text: NCERT Chapter 7 (NCERT, Class 11 Physics Part I)

Physics Notes for NEET and JEE Main: All Chapters

• Units and Measurement
• Motion in a Straight Line
• Motion in a Plane
• Laws of Motion
• Work, Energy and Power
• Systems of Particles and Rotational Motion
• Gravitation
• Mechanical Properties of Solids
• Mechanical Properties of Fluids
• Thermodynamics
• Kinetic Theory of Gases
• Oscillations
• Waves
• Thermal Properties of Matter
• Electric Charges and Fields
• Electrostatic Potential and Capacitance
• Current Electricity
• Moving Charges and Magnetism
• Magnetism and Matter
• Electromagnetic Induction
• Electromagnetic Waves
• Ray Optics and Optical Instruments
• Wave Optics
• Dual Nature of Radiation and Matter
• Atoms
• Nuclei
• Semiconductor Electronics

All chapters with key points and notes PDFs are on the Physics notes for NEET and JEE Main page.

Gravitation Notes for NEET and JEE Main FAQs