Mnemonics Gravitation - Physics Class 11 - NEET PDF Download

Master the complexities of gravitation with ease! This document provides creative and efficient mnemonics for key concepts like escape velocity and Kepler's laws, ensuring quick understanding and application in numericals. Accelerate your learning journey with these memorable tools!

1. Universal Law of Gravitation

Mnemonic: Gravity Makes Masses Meet… but distance defeats it!

• Gravity → G
• Makes → $m\_1$m₁
• Masses → m₂
• Meet → Force of attraction $F$F
• Distance defeats it → r² in denominator (greater distance → weaker force)

Explanation:

Newton’s Universal Law of Gravitation states that every particle in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres. This force acts along the line joining their centres and is always attractive in nature. Mathematically,

where $G$G is the universal gravitational constant.

2. Escape Velocity

Mnemonic: "Whole Root Two Gravity Rocket Escapes at 11.2!"

• Whole Root: Indicates the square root symbol in the escape velocity formula: 
• Two: Refers to the factor of 2 in the formula.
• Gravity: Represents $g$g, the acceleration due to gravity.
• Rocket : Represents Radius of the planet ($6.37\times 10\mathrm{<sup\; style="font-size:12px\; !important">6</sup>}$m for Earth)

• Escapes: Highlights that the escape velocity is the speed needed for a rocket or object to escape Earth's gravitational pull.

• At 11.2: Refers to the approximate escape velocity of Earth, which is 11.2 km/s.

Explanation:

Escape velocity is the minimum speed an object must be given so that it can move away from a planet indefinitely, without any additional engine force, and without being pulled back by gravity.

It is derived by equating the object’s kinetic energy to the gravitational potential energy needed to escape the planet’s gravitational field:

This gives:

Will be used in many numericals. So learn the formula!

3. Kepler's Laws of Planetary Motion

Mnemonic: "Planets Eat Fruits at Equal Interval 2/3 Times"

•  Planet Eat Fruits  - Refers to Kepler's First Law: Planets move in Elliptical orbits, with the Sun at one of the Foci.
• Equal Interval - Refers to Kepler's Second Law: A line joining a planet and the Sun sweeps out Equal areas in Equal intervals of time, irrespective of the planet's position in its orbit.
•  2/3 Times" - Refers to Kepler's Third Law: The square of the planet’s orbital period (T²) is proportional to the cube of the semi-major axis (R³)

Explanation: 

Kepler’s Three Laws describe how planets move around the Sun:

1. First Law (Law of Orbits):
   Each planet moves in an elliptical orbit with the Sun at one focus, not at the center.
   This explains why planets speed up and slow down at different points in their orbit.

2. Second Law (Law of Areas):
   A line joining the planet and the Sun sweeps out equal areas in equal intervals of time.
   This means planets move faster when closer to the Sun (perihelion) and slower when farther away (aphelion).

3. Third Law (Law of Periods):
   The square of the planet’s orbital period T is proportional to the cube of the distance (semi-major axis) $R$R:

   $T^2\; \backslash propto\; R^3$T² ∝ R³

   This shows that farther planets take much longer to complete one orbit.