Physics 1: The Earth and the Universe

How does the sun produce light?

• Nuclear Fusion: when the larger hydrogen nuclei combine to form smaller helium nuclei in high temperature and pressure in the Sun to produce large amounts of energy. Larger stars can fuse helium nuclei to form atoms lik carbon, oxygen and iron etc.

How were the stars and planets formed?

• The solar system was formed 4.6-5 billion years from a cloud of stellar dust in a nebula. The cloud began to collapse because of a shockwave from a nearby exploding star causing the forces to imbalance. When it collapsed a flat disc of material was formed and at the cntre the large amount of pressure caused the fusion of hydrogen which eventually formed the Sun and released a large amount of energy.  The remaining  material clumped together due to gravity to form planets and dwarf planets. Smaller rocky planets like the Earth formed near the Sun whereas the larger icy and gaseous planets formed futher away due to the high temperatures near the sun. 

What is the Big Bang?

• The theory states that originally all the matter in the universe was concentrated into a single incredibly tiny point. This began to enlarge rapidly in a hot explosion (called the Big Bang), and it is still expanding today. The Big Bang happened about 13.7-14 billion years ago

What are nine planets in order from the Sun?

• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto

Define Meteorite, Asteroid, Comet and the Moon

• METEORITE: a piece of rock or metal that has fallen to the earth's surface from outer space as a meteor. Over 90 per cent of meteorites are of rock while the remainder consist wholly or partly of iron and nickel.
• ASTEROID: a small rocky body orbiting the sun. Large numbers of these, ranging enormously in size, are found between the orbits of Mars and Jupiter, though some have more eccentric orbits.
• COMET: a celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun.
• MOON: the natural satellite of the earth, visible (chiefly at night) by reflected light from the sun. A satellite is an objects that orbits another object

What is a light year?

• A unit of astronomical distance equivalent to the distance that light travels in one year, which is 9.4607 × 10¹² km (nearly 6 million million miles). Light travels at the speed of 3x10⁸ m/s. in a vacuum
• So light from the Sun takes 8 minutes to get to Earth. Thus when looking at distant objects they look younger than they are

What is relative brightness and its limitations?

• Relative brightness can be used to measure the distance of stars. A star can look brighter if it is bigger than other stars, closer or hotter. The difference in brightnes can be sued to measure how far it is.
• Light pollution makes it harder to see stars so only the few brightest can be seen. The atmospheric gas absorbs some light coming from the stars.

What is parallax?

• A change in the apparent position of an object relative to more distant objects, caused by a change in the observer's line of sight towards the object. 

How much bigger is the diameter of the Sun than the Earth?

• The Sun's diameter is about 100 times bigger than the diameter of the Earth 
• The Milky Way Galaxy is about 6 billion times the diameter of the Sun

SIZE from smallest to biggest:

• Diameter of the Earth
• Diameter of the Sun
• Diameter of the Earth's orbit 
• Diameter of the Solar System
• Distance from the sun to the nearest star
• Diameter of the Milky Way
• Distance from the Milky Way to the nearest galaxy 

What are the ages of the Sun, Earth and Universe?

• The Universe started expanding from a single point 14000 million years ago
• The Sun was formed 5000 million years ago and the Earth was formed 4500 million years ago

What is redshift?

• For visible light red has the longest wavelength and violet the shortest. When a source moves away from an observer, the observed wavelength increases and the frequency decreases.
• When we look at the spectrum of a distant star, we still see an absorption spectrum. However, the pattern of lines has moved towards the red end of the spectrum
• The positions of the lines have changed because of the Doppler effect. Their wavelengths have increased (and their frequencies have decreased).
• Astronomers have found that the further from us a star is, the more its light is red-shifted. This tells us that distant galaxies are moving away from us, and that the further away a galaxy is, the faster it's moving away.
• Since we cannot assume that we have a special place in the Universe, this is evidence for a generally expanding universe. It suggests that everything is moving away from everything else.

What is the ultimate fate of the universe? The Universe's ultimate fate depends on how fast its expanding and the total mass:

• To calculate how fast its expanding we need to be able measure long distances but the Universe is too large to measure it accurately
• an we need to observe the motion of the objects but light pollution hinders this
• It is also hard to measure mass becuase most of it is invisble light/dark matter which can only be detected by the way it affects the movement of objects we can see

Some say the Universe will continue to expand neverendingly. I there is too much mass the gravity will be strong enough to pull everything back together and it will collapse with the Big Crunch

What is Wegener's theory? He proposed the idea that all the continents were once joined together in the supercontinent Pangaea but had drifted apart 

Evidence:The continents fit together like a jigsaw. There were fossils of the same land animals on different continents. The mountain ranges and sedimentary rock patterns matched up on different continents

Rejection: He was a meteorologist( an amateur geologist) so his findings were not taken seriously. There was no mechanism as to how the continents had drifted and no one could feel the movements of the continents. Also there were other theories like the Land Bridge Theory that explained the evidence better.

Acceptance: In the 1950s they found that in the Mid Atlantic Ridge magma was rising up through the seafloor and solidifying to form underwater mountains either side of the ridge - which showed the seafloor was spreading. As well as that they found that as the magma erupted out the gaps the iron particles aligned themselves to the Earths magnetic field. The Earth's magnetic field swapped direction every half a million years so the rocks had alternating bands of magnetic polarity. Which convinced people that the seafloor was spreading and the continents had drifted.

What is a P Wave?

• P-waves (P stands for primary) arrive at the detector first. They are longitudinal waves which mean the vibrations are along the same direction as the direction of travel. Other examples of longitudinal waves include sound waves and waves in a stretched spring.

What is a S Wave?

• S-waves (S stands for secondary) arrive at the detector of a seismometer second. They are transverse waves which mean the vibrations are at right angles to the direction of travel. Other examples of transverse waves include light waves and water waves.

How can they be used?

• Both types of seismic wave can be detected near the earthquake centre but only P-waves can be detected on the other side of the Earth. This is because P-waves can travel through solids and liquids whereas S-waves can only travel through solids. This means the liquid part of the core blocks the passage of S-waves.

Amplitude: As waves travel, they set up patterns of disturbance. The amplitude of a wave is its maximum disturbance from its undisturbed position. Take care: the amplitude is notthe distance between the top and bottom of a wave. It is the distance from the middle to the top.

Wavelength: The wavelength of a wave is the distance between a point on one wave and the same point on the next wave. It is often easiest to measure this from the crest of one wave to the crest of the next wave, but it doesn't matter where as long as it is the same point in each wave.

Frequency: The frequency of a wave is the number of waves produced by a source each second. 

The speed of a wave - its wave speed (metres per second, m/s)- is related to its frequency (hertz, Hz) and wavelength (metre, m), according to this equation:

wave speed = frequency x wavelength