Physics Definitions: Fields, Work, Gravity, and Orbital Motion

Fundamental Concepts of Fields and Work

Force Fields

A force field exists in a space if, by placing a test body within it, this body is subjected to a force.

Types of Fields

• Uniform Field: Force vectors have the same magnitude and direction at all points in space.
• Central Fields: The directions of all force vectors converge on a single point.

Work and Energy Transfer

Work is a mechanism of energy transfer between systems when a force acts.

Conservative Fields

Conservative Fields: Those in which the work done by the field force is independent of the path taken, depending only on the initial and final points.

• The work done by the field force along a closed path is zero.
• In a conservative field, work done against the field force is not lost; it is stored as potential energy.

Work-Energy Theorem

The Work-Energy Theorem: The work done by a force, regardless of its nature, is equal to the change in kinetic energy.

Principle of Conservation of Mechanical Energy

The Principle of Conservation of Mechanical Energy: When a conservative force acts on a body, mechanical energy is conserved, meaning kinetic energy (Ec) can convert to potential energy (Ep) and vice versa.

Gravitational Fields

Gravitational Field Strength

Gravitational Field Strength: The force exerted on a unit mass when it is at that point.

Principle of Superposition

The Principle of Superposition: The gravitational field created by a distribution of point masses is equal to the sum of the fields created by each individual mass.

Gravitational Potential Energy

Gravitational Potential Energy (Ep): At a point A, it is defined as the work that the gravitational field force must do to move a body from point A to infinity.

Gravitational Potential at a Point

Gravitational Potential at a Point: It is defined as the work that the gravitational field force must do to move a unit mass from that point to infinity. It is also the potential energy acquired by a unit mass at that point.

Equipotential Surfaces

Equipotential Surfaces: Surfaces where all points have the same potential value.

Gravitational Flux

Gravitational Flux: The amount of gravitational field lines passing through a surface.

Earth's Gravitational Field & Orbital Mechanics

Gravitational Field Intensity (Earth)

Gravitational Field Intensity (Earth): The force with which the Earth attracts a unit mass at a given point.

Weight

Weight: The force with which the Earth attracts a body located at a point in its gravitational field.

Earth's Gravitational Potential Energy

Earth's Gravitational Potential Energy: The energy acquired by a body of mass 'm' when placed at a point in Earth's gravitational field.

Orbital Speed

Orbital Speed: The speed required for a satellite to maintain a stable orbit.

Escape Velocity

Escape Velocity: The minimum speed required for an object to escape the gravitational influence of a massive body, such as Earth.

Geostationary Satellite

Geostationary Satellite: A satellite that orbits Earth with the same period of revolution as Earth (24 hours), appearing stationary relative to a point on the ground.

Kepler's Laws of Planetary Motion

Kepler's First Law

Kepler's First Law: All planets move in elliptical orbits with the Sun located at one focus.

Kepler's Second Law

Kepler's Second Law: The radius vector joining a planet to the Sun sweeps out equal areas in equal intervals of time. This means the areal velocity is constant, and planets move faster when closer to the Sun.

Kepler's Third Law

Kepler's Third Law: The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit (average distance to the Sun).