COSMOS AND MOTION: SEMESTER ONE

Focus Point One: The universe is held together by gravity.

-Distinguish between the terms mass and weight.

-Define gravitational attraction as a force that exists between any two bodies that have mass.

-Calculate acceleration due to gravity on the surface of the earth and other planets in the solar system

Mass is defined as the property of a body that causes it to have weight in a gravitational field. Can be measured in kilograms, grams etc. Weight is a measure of the force needed to support an object in a neutral gravitational field. This can be measured in Newtons.

Gravitational attraction exists between any two bodies that have mass and is a fundamental force (other such forces are electromagnetic and nuclear). It causes objects to be attracted towards each other and the magnitude of this force between two bodies is related to the mass and the distance. The Universal law of gravitation was devised by Isaac Newton and can be represented by:

Where F= force measured in newtons, m= mass measured in kilograms, d or r = distance in metres and G is the Universal Gravitational constant of 6.67 time 10 negative eleven.

The value of G is very small so gravity is only noticeable when at least one object with a very large mass is involved. Close to the surface of the Earth, when an object is allowed to fall, it moves in a straight line towards the centre of the Earth. The further the object falls, the faster it moves, thus it is accelerating. The value of acceleration, if the effects of air resistance are ignored, is a constant regardless of the mass of the object that is falling. The acceleration due to gravity on any planet can be calculated using the following formula:

Where M= mass of planet and r= radius of planet and G= universal Gravitational constant.

The rate of acceleration due to gravity has been accurately measured to be 9.8 ms (power of negative 2)

If the force of gravity between objects had:

1. The separation double the force would be quartered.

2. The separation halved the force would quadruple.

3. One mass doubled, the mass would have twice the pull of gravity.

4. One mass doubled and one mass halved the gravity would stay the same.

ASK about One over distance squared.

Focus Point Two: Travel to the other parts of the solar system uses rockets and gravity.

-Identify Newtons three laws of motion and examples.

-Apply Newtons laws to explain how a rocket works.

-Define speed, acceleration and force.

-Solve problems using the equations of motion.

Isaac Newton came up with three laws of motion, and these were:

1. A body persists in a state of rest or uniform motion unless acted on by an external unbalanced force. Often called the law of inertia.

2. The relationship between an objects mass m, and its acceleration a is represented in the equation F=ma, the greater the mass of an object accelerating the greater the force needed to accelerate the object. Acceleration is produced when a force acts on a mass and can involve a change of direction as well as speed.

3. For every action there is an equal and opposite reaction. So, for every force there is a reaction equal in size and opposite in direction. Remember Georgia and Cat on the chairs.

Newtons third law of motion is used to assist the movement of a rocket. The rockets action is to push down against the ground with its powerful engine. The equal and opposite reaction is the rocket is pushed upwards off the ground.

Speed is defined as the rate of motion, or rather, the rate of change of distance.

V (av) = d/t

Where V (av) = average speed, d= total distance travelled and t= total time taken to travel distance. Instantaneous speed is the speed at one instant in time.

Velocity is the speed of a body in a given direction, viz a change in displacement over time where displacement is the distance from a given point in a given direction. Velocity should include a distance in metres and a direction. Acceleration is defined as the rate of change of velocity. It can involve a change in magnitude or direction, and is written as ms (-2).

A (av) = v/ t

Where a (av) = average acceleration, triangle v= change in velocity of the body and triangle t= change in time over which the change in velocity took place.

Alternatively one may write:

A (av) = (v-u)/t

Where a(av)= average acceleration, v= final velocity of the body, u= initial velocity of the body and t= time over which the change took place.

A force is a push or pull which can cause an object with mass to change its velocity.

Problems can be solved using the equations of motion. The equation for acceleration can be rearranged as:

V= u+at; U= v-at; T=v-u/ a

To find final velocity, initial velocity and time over which a change took place.

SEE CORE SCIENCE TEXTBOOK

Focus Point Three: Our knowledge of the universe is based mainly on the interpretation of electromagnetic radiation that arrives on earth.

-Review the nature of electromagnetic radiation.

-Describe how waves can be reflected and refracted and relate this to the working of optical and radio telescopes.

-Describe difficulties that telescopes encounter in gathering information from the universe including absorption by atmosphere, light pollution, immensity of the distances, loss of intensity with distance. Unlike a mechanical wave in which the particles in a medium are disturbed, electromagnetic waves do not require a medium for their propagation. They involve the propagation of oscillating electric and magnetic fields and are transverse waves. A transverse wave is a moving wave that consists of oscillations occurring perpendicular to the direction of energy transfer. It the wave is moving horizontally, its oscillations will move vertically. They travel at their highest velocity in a vacuum while they move slightly slower through matter. Electromagnetic waves vary in their frequencies and wavelengths although their velocities are the same in a vacuum. The collection of different frequency waves is the electromagnetic spectrum and is seen below:

Band NameWavelength (approx.)Sources of WavesUses of Waves

Radio/TV100Km-10mRadio/TV transmittersRadio/TV communication, radio astronomy and telescopes.

Microwave10mm-0.1mmRadar transmitters, microwave ovensSatellite communication, cooking food

Infrared0.1 mm-0.001 mmElectric radiatorsHeating rooms, medical heat treatments, night vision systems.

Visible light400 nm-700 nmStars, electric lampsHuman vision, photosynthesis, photography, astronomy

Ultraviolet400 nm-1 nmUV lamps, starsUV astronomy, sterilization

X-Rays1 nm- 0.001 nmX-ray tubes, black holesMedical radiography (diagnosis and treatment, flaws in structural materials, x-ray astronomy

Gamma Rays0.01 nm- 0.0001 nmRadioactive mineralsSterilization, killing cancer cells.

Astronomers use various bands of the electromagnetic spectrum to investigate the universe. For example:

Radio waves are used in radio telescopes. These are large dishes (such as those in Parkes) that collect radio waves from space. The weak radio signals are amplified and analyzed. Radio astronomy is used to observe objects that emit mainly radio waves rather than visible lights such as dark nebulae (very dense interstellar cloud that obscures light), quasars (very energetic and distant galaxy with high red shift and a galactic nucleus), and pulsars (rotating stars that emit beams of electromagnetic radiation). They also observe clouds of hydrogen in deep space.

Infrared waves are used in telescopes and their spectrometers to detect objects that are too cool to emit visible light, measure the temperature of the atmosphere of the solar system planets and determine the temperature of the background radiation in deep space.

Visible Light allows for ground based optical telescopes and spectrometers as well as space telescopes such as the Hubble. These are used to observe and measure optical sources such as planets, comets, stars and galaxies; measure the red shift of space objects such as galaxies to determine the extent of the expansion of the universe. They also allow for measurement of the colour and temperature of stars.

It is important to note that ground based astronomy is faced with many difficulties. These include:

i. Earths Atmosphere: The atmosphere absorbs various components of the electromagnetic spectrum. Infrared, UV and X-Rays are significantly absorbed by the atmosphere. Visible light is scattered and refracted by the atmosphere and clear images are hard to obtain. Locating telescopes on high mountains and using modern adaptive optics slightly improves the quality of the signals detected.

ii. Light Pollution: Cities emit a large amount of visible light at night so telescopes are mainly built where there is little visible light pollution. iii. Radio Wave Pollution: Mobile phones, microwave sources and satellite TV transmissions make it difficult for radio astronomers to detect weak radio signals from space.iv. Solar Storms: Solar Flares release bursts of electromagnetic radiation that interfere with other electromagnetic sources in space.v. Optical systems in Telescopes: Lenses and mirrors in telescopes produce some degree of distortion of images. Telescopes are limited by their resolution. Resolution is the ability of an optical system to distinguish between two close objects. Ground based astronomy is also affected by the immense distance over which electromagnetic radiation information has to travel and the loss of data over this distance.

There are two types of telescopes, radio and optical. Optical telescopes can be of two types, reflecting and refracting.

Radio telescopes can detect and collect data on radio sources. These telescopes generally have a wide parabolic dish shape and are placed far major population centers, usually in valleys to shield them from EMI. (Optical telescopes are placed on high mountain tops.) A notable development came with radio interferometry. This involves arrays of parabolic dishes being widely separated and connected with cables, optical fibers etc. This increases the total signal collected and increases resolution. Basically means combining the images from the different telescopes.

Optical telescopes are used to gather and focus light mainly from the visible part of the electromagnetic spectrum. The basic scheme is that the convex or concave mirror is used to gather the incoming light and focuses that light onto a focal plane where it forms a real image that can be viewed or recorded through an eyepiece which acts as a magnifying glass.

Reflecting Telescopes:

A reflecting telescope uses a curved mirror to focus light. Light from distant objects, such as stars and galaxies, enters the telescope in parallel rays. These rays are reflected from the concave objective mirror to a diagonal flat mirror. This mirror reflects the light from the side of the telescope to an eyepiece lense which magnifies the image.

Refracting Telescopes:

The simplest refracting telescope has two convex lenses which are thicker in the middle. The lense closest to the object is the objective lense. This lense collects light from a distant light source and brings it to focus as an upside-down image within the telescope tube. The eyepiece lense forms an image that remains inverted. More complex refracting telescopes include an extra lense to flip the image.

Focus Point Four: Electromagnetic radiation from the universe can be used to determine the size and temperature of stars and their distance to the Earth.

-Relate temperature to wavelength of radiation emitted from hot bodies.

-Explain how the colour of a star can be used to estimate its surface temperature.

One way astronomers can learn about a star is by analyzing its light. They do this by transferring light from a telescope through a spectroscope. By comparing and analyzing patterns in the spectra of stars, astronomers can infer star compositions and temperatures.

Another way to study starlight is by examining the intensity of light emitted as various wavelengths. The intensity of light can be shown in a graphical representation of a spectrum. The graphical spectra show intensity on the y-axis and wavelength along the x-axis. The wavelength reported at the peak is where the star emits the highest amount of energy. The peak emission wavelength is related to the stars colour.

The colors of stars are directly related to their temperatures. From coolest to hottest, stars appear red, orange, yellow, white and blue. The peak emission wavelength determines a stars colour, and colour indicates temperature so peak emission wavelength (PEW!) determines colour. Note below that the brightest colour corresponds to the PEW(!). Studies of stellar spectra allow astronomers to develop and refine models of stellar evolutionthe processes by which stars of different sizes are formed, live and die.

Focus Point Five: Stars are part of a dynamic universe and change over time.

-Describe the sequence of stellar evolution and relate different pathways to mass (nebula-protostar-main sequence-red giant/supergiant-white dwarf/black hole/neutron star-brown dwarf.

-Classify stars using a HR diagram

-Extract information from HR diagram and recognize the following groups- main sequence, red giants, white dwarfs, and supergiant.

Stellar Evolution is the process by which a star undergoes a series of radical changes during its lifetime. Depending on the mass of the star, this ranges from only a few million years to a trillion. Stellar Evolution was not studied by observing the lifetime of a single star (impossible), but rather by observing numerous stars and simulating stellar structure with computer models.

When the universe came into existence, around 14 billion years ago, the only elements were hydrogen, helium and traces of lithium, beryllium and boron. The heavier elements did not yet exist. Heavy elements are produced by nucleosynthesis, the fusion of nuclei deep inside stars that releases energy. The outflow of energy from the central regions of a star provides the pressure necessary to keep the star from collapsing inwards.

A star collapses when the fuel deep inside it is used up and the energy flow from the core stops. Nuclear reactions outside the core cause the star to expand outwards in the red giant phase before it begins its inevitable collapse. If the star is about the same mass as our sun, it will become a white dwarf. If it is more massive, it will undergo a supernova explosion and leave behind (NOT BECOME) a neutron star. If the collapsing core of the star is very great, it will collapse inwards and form a gravitational warp in space; a black hole.

Stars are formed in giant clouds of dust and gas and progress through their normal life as balls of gas heated by thermonuclear reactions in their cores. Depending on their mass, they reach the end of their evolution as a white dwarf, neutron star or black hole. The cycle begins anew as an expanding super shell from one or more supernovas can trigger the formation of a new generation of stars. Brown dwarfs have a mass only a small percentage of that of the sun so they never evolve.

SEE SHEET FOR DIAGRAM OF STELLAR EVOLUTION

The Hertzsprung-Russel diagram (HR diagram) plots luminosity or absolute magnitute as a function of temperature or colour for stars. It also demonstrates stellar evolution.

ASK SUN TO EXPLAIN CETTE DIAGRAM

Focus Point Six: Our understanding of the nature of the universe has changed over time and the latest theory is the big bang.

-Outline the features of nebulae, stars, galaxies, planets, quasars, black holes

-Identify and describe the main features of the big bang theory

-Recall the main features of a scientific theory and a law

-Outline evidence for the Big Bang Theory

-Outline some previously accepted ideas about the origin of the universe and explain why they were replaced by the Big Bang Theory

Nebulae: A nebulae is an interstellar cloud of dust, hydrogen, helium gas and plasma. They often form in star-forming regions. In these regions the clouds of dust clump together to form larger masses, which attract further matter and eventually become stars. The remaining objects form planetary system objects (This is believed.)

Stars: A star is a massive luminous ball of plasma held together by gravity. For most of its life, a star exists on energy produced by thermonuclear fusion and they vary widely on size and temperature. See more before.

Galaxy: A galaxy is a massive gravitationally bound system that consists of stars and stellar remnants, a medium of gas and dust, and an important but poorly understood component dubbed dark matter (This cannot be detected from its radiation, but from its gravitational effects on visible radiation). Historically, galaxies are categorized according to shape, and these include elliptical, spiral and peculiar galaxies. Galaxies may contain planets, stars and other planetary system objects.

Planets: A planet is, by definition, a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion and has cleared the surrounding area of space litter (not actually a word, the correct term is planetisimals). All planets revolve around stars, have varying degrees of axial tilt, rotate around invisible axis in their centre and have cleared their neighborhood. Larger planets have larger atmospheres.

Quasars: Quasars are powerfully energetic and distant galaxies with an active galactic nucleus and show a very high red shift. It follows that quasars are very ancient and they radiate at high rates. They are believed to be massive black holes in the centers of galaxies.

Black Holes: A black hole is a region of space in which the gravitational field is so powerful that nothing, including light, can escape. A black hole has a surface called an event horizon through which objects can fall but not escape. It is called black as it absorbs all light and reflects nothing. As, for example, gases fall into a black hole they emit large amounts of radiation and become very hot, making it possible to detect black holes from earth.

Other useful terms include:

Hypothesis: A hypothesis is a limited statement regarding cause and effect in a specific situation and can be tested by experimentation and observation or by statistical analysis of the probabilities from the data obtained. The outcome of the test should be unknown so the results can provide data regarding the validity of the hypothesis.

Model: A model is used for situations when the hypothesis has a limitation in its validity. It is by no means a representation of the true nature of the subject but is useful in determining features and so on.

Law: A statement of fact meant to describe in concise terms, an action or set of actions. It is generally accepted to be both true and universal and can sometimes be expressed as a single mathematical equation. They must be simple, universal and absolute.

Theory: An explanation of a set of related observations or evens based upon proven hypotheses and verified multiple times by detached researchers. It is more complex and dynamic than a law and explains an entire group of related phenomena. Components of it can be changed or improved upon without changing the overall truth of the theory as a whole.

SEE SHEETS FOR SCIENTIFIC METHOD

The Big Bang model had its beginnings with Edwin Hubbles discovery that everything in the universe is moving away from everything else or expanding in every direction. This is known as Hubbles law. It follows that there was a time when the universe was an infinitesimally small point. It was not an explosion IN the universe but rather OF the universe. The evidence for the Big Bang is as follows:

1. The first line of evidence is the expansion of the universe. It is to be noted the universe must have been always expanding as there is no mechanism which could accomplish a transition from shrinking to expanding on a universal scale.

2. The second part of the evidence is Cosmic Microwave Background Radiation (CMB) which is left over from the first light in the universe and is a very strong indication that the Big Bang occurred.

3. The third pillar lies in the abundance of different elements in the universe. The Big Bang theory predicts certain amounts of hydrogen and helium and observations have recorded almost exactly these amounts.

4. The fourth piece is red shift, phenomena which occurs when electromagnetic radiation is shifted towards the less energetic end of the electromagnetic spectrum. It is defined as an increase in the wavelength of radiation received compared to the wavelength emitted. Conversely, a decrease is called blue shift. Red shift occurs when a light source moves away from an observer further proving that the universe is expanding.

Another theory proposed as an alternative to the Big Bang theory was the Steady State theory which asserted that although the universe was expanding, it did not change its look over time. For this to work, new matter would have to be formed which contradicted the law of conservation of matter. It removed the need for the universe to have a beginning. The steady state theory claims that CMB arose from light from ancient stars scattered by galactic dust, however this does not comply as CMB is very smooth making it difficult to explain how it arose from point sources. After the Steady State Theory was rejected, it was altered to be the basis for another theory known as the quasi-steady state theory which postulates a lot of smaller big bangs occurring over time.