Physics revision test 2 Flashcards
Name the eight planets in order
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
What is the sun
A star
Name a natural satellite
Moons
Where is the asteroid belt situated?
Between Mars and Jupiter
What are comets?
Frozen rocks that move around the Sun, often in very elliptical orbits
Where is our solar system?
In the Milky Way Galaxy
How was the sun formed?
1) A nebula was pulled together by gravitational attraction
2) The particles in the cloud got faster and collided more
3) The gas warmed up and became hot enough to glow (Protostar)
4) The protostar gets more dense, more collisions take place, and it gets hotter
5) The cloud gets hot enough for Hydrogen atoms to fuse, forming Helium (Main Sequence Star)
When was the sun formed?
4.5 billion years ago
Why does the sun remain in the Main Sequence stage?
The gravitational attraction still pulling on the gas is balanced by the outward force of the radiation from the nuclear fusion in the core. The forces are in equilibrium
Why do we have uranium?
Uranium (and other heavy elements naturally present on earth) can only be formed in a supernova explosion, so the sun must have formed from the remnants of a supernova
What will eventually happen to the Sun?
The star runs out of Hydrogen, its core collapses and the outer layers swell, cool and become a Red Giant.
Helium and other elements in the core fuse to form heavier elements. When there are no more light elements in the core, fusion stops and no more radiation is released. The star collapses and becomes a white dwarf. The stars eventually fade out, becoming black dwarfs
What would happen if the Sun was much bigger?
Bigger stars become red supergiants, then they collapse. The collapse is more violent and a supernova explosion occurs. Elements that are heavier than Iron can form from fusion.
The explosion compresses the core into a neutron star - an extremely dense object made of only neutrons. If the original star is massive enough, it becomes a black hole.
Why can we not see black holes?
The gravitational field of a black hole is so strong nothing can escape from it, not even light
What is a planet?
A planet orbits a star, enough gravity to make it spherical and sweeps out its own orbital path of other smaller objects
What is a satellite?
A satellite is something that orbits something else
What is a moon?
A moon orbits a planet
Give an example of a natural satellite:
The moon
T/F: There are artificial (man-made) satellites
True
What force allows planets and satellites to maintain their circular orbit?
Gravity. It is an example of a centripetal force because it is acting towards the centre of a circle
Describe a circular orbit
An object orbits another object at a constant speed. Its direction is constantly changing, so its velocity is changing. Therefore we say an object is accelerating towards the centre of the circle.
What is acceleration?
Change of velocity per second
What happens to the orbit of an object if its speed changes?
If an object in orbit slows down, it will fall into a lower orbit. If it gets too slow, it will crash to the surface.
If an object in orbit speeds up, it will move to a higher orbit. If it gets sufficiently fast, it will escape the gravitational pull of the object and fly off into space.
At the correct speed an object will orbit at a constant height and speed.
What is red shift?
Light waves are stretched out if a star or galaxy is moving away from an observer. The wavelength of the light increases. This is called red shift because the light is shifted towards the longer wavelength - red end of the visible spectrum
What is blue shift?
Light waves are shortened if a star or galaxy is moving towards the observer. The wavelengths would be compressed, making the wavelength shorter. When this occurs, we say the light has been blue shifted
What is red shift evidence for?
The faster a star or galaxy is moving away from the observer, the greater the effect of red shift. Red shift is observed in the large majority of galaxies so they are moving away from us and the more distant ones are moving away faster (speed of recession).
What did Edwin Hubble suggest (Hint: red shift)
Red shift is evidence for the universe expanding because everything is moving away from everything else
What does the big bang theory suggest?
The universe is expanding and originated as a very small and extremely hot and dense region. Red shift provides evidence for this theory because at some point earlier in time, the light must have been extremely short wavelength (high energy) and everything moving apart suggests that everything came from one point.
What other evidence is there for the big bang theory?
In 1965, scientists discovered microwaves coming from every direction in space. This microwave radiation had been red shifted, suggesting that 13.5(ish) billion years ago, there must have been a massively energetic event in one place to still have evidence of it today.
What does CMBR stand for?
Cosmic Microwave Background Radiation
What was the state theory?
The state theory suggested that the universe was expanding, but it had always been there and matter was created into the spaces that the universe expanded into. The state theory is no longer used as new data and evidence has been discovered.
What will happen to our universe?
Depending on the total mass of matter int he universe (unknown because we still have not observed dark matter, a strange substance that is needed for galaxies to maintain their shape) the universe could:
1. [If the universe is less dense than a certain amount] expand forever, the stars will gradually die out and the universe will cool (big yawn)
2. [If the universe is more dense than a certain amount] stop expanding and collapse (big crunch) - some scientists currently think the universe has gone through cycles of this.
