Self-gravity is a. the gravitational pull of a person. b. the force that holds objects like people and lamps together. c. the gravitational interaction of all the parts of a body. d. the force that holds objects on Earth.

Gravitational interaction is the force that attracts two masses towards each other. It's a fundamental force of nature described by Isaac Newton's law of universal gravitation. This law states that every mass exerts an attractive force on every other mass. The formula for gravitational force is given by \[ F = G \frac{m_1 m_2}{r^2} \]where \( F \) is the force between the masses, \( G \) is the gravitational constant, \( m_1 \) and \( m_2 \) are the masses, and \( r \) is the distance between the centers of the two masses.
Every object in the universe with mass experiences gravitational interaction.
However, when we talk about self-gravity, we are referring to the gravitational interaction within different parts of a single body.

• This means, for example, a planet or a moon, where every part of the body is pulling every other part towards itself.
• This internal attraction helps in giving the body its shape and structure.

Internal forces are those forces that act within an object or system. These forces differ from external forces, which act from outside the system.
For self-gravity, internal forces are crucial as they are responsible for the gravitational pull between the various parts of the object itself.
Understanding internal forces helps explain why planets are spherical, and mountains can only reach certain heights before they collapse under their weight.The balance of internal gravitational forces is what keeps celestial bodies everywhere in space, held together.

• In a star, for instance, the self-gravity trying to collapse the star is balanced by the outward pressure from nuclear fusion.
• For smaller objects like asteroids, their self-gravity helps keep them together even though they might not be perfectly round.

Gravity in objects, especially large celestial bodies, plays a key role in their formation and structure.
This gravity is the cumulative effect of self-gravity and is what makes stars, planets, and moons spherical over time.
Self-gravity refers specifically to the gravitational pull among all the parts within that single object. This is what ensures that objects are coherent and do not fly apart.

• For example, in a planet like Earth, self-gravity ensures that the particles of rock and water stick together to form our world.
• In larger objects like galaxies, gravity ensures that numerous stars are held in the galaxy without drifting away.

Without self-gravity, objects in space would find it difficult to maintain their shape and could easily disintegrate.
Self-gravity is crucial for understanding phenomena like Earth's tides, where the gravitational pulls from different parts of the Earth and the Moon create the rise and fall of water levels.