Rotational motion and astrophysics

A line touching at one point, acting at 90 degrees to a particular point

Moving towards or in a central direction

The time for one revolution measured in seconds

The number of revolutions per second measured in hertz

The time rate of change or angular velocity of a rotating body, denoted by the Greek letter alpha

A property of matter which resists change in motion or movement

A measure of an object’s resistance to angular acceleration about a given axis

A force acting in a perpendicular direction that causes an object to rotate about an axis

The quantity of rotation of a body. It is given as the product of the moment of intertia and angular velocity. If no external torque acts on a system, the angular momentum of the system will remain constant. This is known as the principle of conservation of angular momentum.

Roughly the mean distance between the Earth and the Sun

A region where an object experiences a force due to its mass

The gravitational force acting on a unit mass

An object which orbits a larger mass

The energy an object of mass has at a point in relation to another massive object due to gravity

The minimum velocity required to allow a mass to escape a gravitational field to infinity, where the mass achieves zero kinetic energy and maximum (zero) potential energy

This refers to a co-ordinate and reference system by which we can determine position and velocities

One where the observer is stationary or moving at a constant speed.

One where the observer is accelerating

It is indistinguishable for an observer to tell if they are in an accelerating object or in a gravitational field

A model where the three dimensions of space are combined with the dimension of time

An incredibly massive object which curves spacetime so that the escape velocity is greater than the speed of light

The boundary of a black hole at which the escape velocity is equal to the speed of light. An event horizon can be defined as the point from which nothing can return. From the perspective of a distant observer, time appears to be frozen at the event horizon of a black hole.

The distance from its centre (singularity) to its event horizon

The embryonic early phase of a star

The total amount of electromagnetic energy (of all forms) radiated by a star

A slightly more subjective description of the luminosity of a star as it refers to the amount of energy reaching the observer which depends also on the distance of the star from us

The nuclear fusion reaction which occurs in our Sun and other stars with core temperatures less than 15 million kelvin