Class 9 Chapter 10 Gravitation : **Definitions**

- Gravitation: Gravitation is the force of attraction between two bodies in the universe. It is responsible for holding planets in their orbits around the sun, and for holding galaxies together.
- Mass: Mass is the amount of matter in a body. It is a scalar quantity and is measured in kilograms (kg).
- Weight: Weight is the force with which a body is attracted towards the center of the earth. It is a vector quantity and is measured in Newtons (N).
- Newton’s law of gravitation: Newton’s law of gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
- Gravitational field: Gravitational field is a region in space where a mass experiences a force due to the presence of another mass. It is a vector quantity and is measured in Newtons per kilogram (N/kg).
- Gravitational potential energy: Gravitational potential energy is the energy possessed by an object due to its position in a gravitational field. It is a scalar quantity and is measured in Joules (J).
- Escape velocity: Escape velocity is the minimum velocity required by an object to escape the gravitational field of a planet or a celestial body. It depends on the mass and radius of the planet.
- Kepler’s laws of planetary motion: Kepler’s laws of planetary motion are three laws that describe the motion of planets around the sun. The first law states that planets move in elliptical orbits with the sun at one of the foci. The second law states that planets move faster when they are closer to the sun and slower when they are farther away. The third law states that the square of the period of revolution of a planet is proportional to the cube of its average distance from the sun.
- Gravitational constant: Gravitational constant (G) is a universal constant that appears in Newton’s law of gravitation. Its value is approximately 6.67 x 10^-11 Nm^2/kg^2.
- Acceleration due to gravity: Acceleration due to gravity (g) is the acceleration experienced by a body when it falls freely under the influence of gravity. Its value is approximately 9.8 m/s^2 near the surface of the earth.
- Gravitational potential: Gravitational potential (V) at a point in a gravitational field is the work done in bringing a unit mass from infinity to that point. It is a scalar quantity and is measured in Joules per kilogram (J/kg).
- Geostationary satellites: Geostationary satellites are artificial satellites that orbit the earth at an altitude of approximately 36,000 km above the equator. They have a period of revolution of 24 hours and appear stationary from the earth’s surface.
- Gravitational force: Gravitational force is the force of attraction between two bodies in the universe due to their masses. It is a vector quantity and is measured in Newtons (N).
- Inertial mass: Inertial mass is a measure of an object’s resistance to changes in its motion. It is equal to the ratio of the force acting on an object to its acceleration.

Above are the important Definitions of **Class 9 Chapter 10 Gravitation**