Astronomical distances are expressed using three specialist units: Astronomical unit: average distance between the Earth and the Sun Light-year: distance travelled by light in a vacuum in a time of one year Parsec: the distance from which a base length (radius) of 1...

# Module 5 – Newtonian world and astrophysics

## Electromagnetic Radiation From StarsElectromagnetic Radiation From Stars

When electrons are bound to their atoms in a gas, they can only exist in one of a discrete set of energies referred to as energy levels. Energy levels are negative because energy is required to remove an electron from the atom; an electron with zero energy is free...

## StarsStars

Astrophysics definitions: Planets: an object in orbit around a star which has 3 characteristics: Mass large enough for its gravitational attraction to give it a round shape No fusion reactions Has cleared its orbit of most other objects, e.g. asteroids Planetary...

## Gravitational Potential and EnergyGravitational Potential and Energy

Gravitational potential energy is the work done in bringing a mass from infinity to the point. It is found by integration – it’s equal to the area under a force-distance graph. For a point or spherical mass, it’s given by Gravitational potential is the GPE per unit...

## Planetary MotionPlanetary Motion

Kepler devised three laws of planetary motion: The orbit of a planet is an ellipse with the Sun at one focus A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time (planets move faster closer to the Sun Most planets in the...

## Newton’s Law of GravitationNewton’s Law of Gravitation

This describes the forces between any objects that have mass. It states that the force between two point masses is: Directly proportional to the product of the masses, Inversely proportional to the square of their separation, These can be combined into a single...

## Point and Spherical MassesPoint and Spherical Masses

Gravitational fields are due to objects having mass. The field extends to infinity, but becomes gets weaker as the distance from the centre of mass of the object increases. It becomes negligible at long distances. The mass of a spherical object can be modelled as a...

## DampingDamping

An oscillation is damped when an external force that acts on the oscillator has the effect of decreasing the amplitude of its oscillations. Light damping causes the amplitude of the oscillator to gradually decrease with time. The period is unchanged. Heavy damping...

## Energy of a Simple Harmonic OscillatorEnergy of a Simple Harmonic Oscillator

During simple harmonic motion, energy is interchanged between kinetic and potential energy. As long as there are no energy losses due to frictional forces, the total (mechanical) energy remains constant. When the kinetic energy is at a maximum, the oscillator is at...

## Simple Harmonic OscillationsSimple Harmonic Oscillations

SHM definitions: Displacement: distance from the equilibrium position Amplitude: the maximum displacement from the equilibrium position Period: the time taken to complete one full oscillation Frequency: the number of complete oscillations per unit time Angular...

## Centripetal ForceCentripetal Force

A constant net force perpendicular to the velocity of an object causes it to travel in a circular path. Such a force can be described as a centripetal force. For an object moving at a constant speed in a circle: Centripetal acceleration is given by: and = yields: =...

## Kinematics of Circular MotionKinematics of Circular Motion

The radian is a measure of an angle. It is defined as the angle subtended by a circular arc with a length equal to the radius of the circle. 2 radians is equal to 360°. The period of an object in circular motion is the time taken for one revolution, whereas the...

## Ideal GasesIdeal Gases

One mole is defined as the amount of substance that contains as many elementary entities as there are atoms in 12g of carbon-12. This number is called the Avogadro constant, NA, and has been measured as 6.02 × 1023. The kinetic theory of gases is a model used to...

## Thermal Properties of MaterialThermal Properties of Material

The specific heat capacity of a substance is how much energy is needed to raise the temperature of 1kg of that substance by 1° You can determine the specific heat capacity of substances in the laboratory: For a metal, use an electric heater to heat a metal cylinder....

## TemperatureTemperature

Bodies are in thermal equilibrium if there is no net flow of energy. This happens when they are at the same temperature. Thermal energy is always transferred from regions of higher temperature to regions of lower temperature. According to the zeroth law of...

## Solid, Liquid and GasSolid, Liquid and Gas

According to the simple kinetic model, solids, liquids and gases are made up of tiny moving or vibrating particles. solid liquid Gas are held tightly and packed fairly close together - they are strongly attracted to each other o are in fixed positions but they do...