### Gravitation

**Gravitational force**

**Mnemonic**: **M.A.D. (Mass, Attraction, Distance)**

• Force of attraction between any two objects having mass
• Acts along a line joining their centers
• **Directly** proportional to the product of the masses of the objects
• **Inversely** proportional to the square of the distance between the objects
• Universal gravitational constant (G):
- **G**oodness **(G)**racious! - Constant of proportionality in Newton’s law of gravitation
- Value: 6.674 × 10^-11 N m^2 kg^-2

**Gravitational field**

**Mnemonic**: **GF-unit (Gravitational Force per unit mass)**

• Gravitational force experienced by a unit mass placed at a point • Represented by the letter g • Direction: Towards the center of the object creating the gravitational field • Magnitude: Equal to the gravitational force acting on a unit mass • Gravitational field intensity (g):

**G**ravity **(g)**otcha! - Ratio of the gravitational force acting on an object to its mass- SI unit: N kg^-1 or m s^-2

**Weight of an object**

**Mnemonic**: **W = m(G)eorge**

• Gravitational force acting on an object due to the presence of another massive object • Depends on the mass of the object (m) and the gravitational field strength (g) • SI unit: N

**Free fall**

**Mnemonic**: **F.F. (Falling Freely)**

• Motion of an object under the influence of gravity alone • Acceleration due to gravity (g):

- acceleration of an object in free fall near the Earth’s surface
- Value: 9.8 m s^-2

**Projectile motion**

**Mnemonic**: **PM-X-Y**

• Motion of an object thrown at an angle to the horizontal • Combination of horizontal and vertical motion • Equations of motion:

**Horizontal motion**: - x = u cos θ t**Vertical motion**: - y = u sin θ t - 0.5 g t^2

**Escape velocity**

**Mnemonic**: **E = mc(s)squared (Escape velocity)**

• Minimum velocity required by an object to escape the gravitational pull of a massive object • For the Earth: 11.2 km s^-1

**Gravitational potential energy**

**Mnemonic**: **GPE = m(G-H)-5**

• Energy possessed by an object due to its position in a gravitational field • Depends on the mass of the object (m), the gravitational field strength (g), and the vertical height of the object (H) • SI unit: J

**Geostationary orbit**

**Mnemonic**: **GEO-stationary: Stationary Satellites above the Equator**

• Circular orbit around the Earth with the same orbital period as the Earth’s rotation • Satellites in this orbit appear to be stationary with respect to the Earth’s surface • Height: Approximately 35,786 km above the Earth’s equator