Tutor profile: Tomas S.
Subject: Physics (Newtonian Mechanics)
Why does the Earth orbit the Sun and not just fly away?
The main reason the Earth orbits the Sun is because there is a gravitational force between the Earth and the Sun that keeps the Sun in orbit. If the Earth were not moving, it would simply be pulled into the Sun and burn up. The only reason the Earth is able to stay in orbit is because it is moving at a high enough speed to not fall into the Sun. The Earth does not fly away because the gravitational force is constantly pulling the Earth back toward the Sun as it travels in its orbit.
Subject: Physics (Electricity and Magnetism)
Describe the process that creates Earth's magnetic field. Where does this process occur within the Earth?
The Earth's magnetic field is created by what is called a dynamo. The liquid iron in the outer core of the Earth is constantly moving around due mostly to the rotation of the Earth. This liquid iron carries a charge with it and charge in motion (or current) produces a magnetic field. The magnetic field that is produced within the core is highly complex and it is thought that the magnetic field lines are dragged around through the core along with the chaotic flow of the liquid iron. At the surface of Earth, however, the field lines look mostly like that of a bar magnetic (with anomalies due to the complexity of flow within the outer core).
Describe the lifecycle of a main sequence star. How does a star form? What elements is it producing at each stage of its life? How does it change in size, mass, and temperature? What does it become at the end of its life?
A star is formed in areas of high gas density (e.g. interstellar gas clouds) that are at very low temperatures (approximately between 10K and 20K). When a gas cloud accumulates a high enough density, it collapses under the weight of its own gravity and clumps into smaller cloud fragments which eventually form what are called protostars. In a protostar, the center is denser than the rest of the cloud, and matter begins falling onto the center until the process of nuclear fusion begins in the star. This star formation process takes ~10 million years. At the first stage of its life, the star fuses hydrogen into helium. Once the star begins to run out of hydrogen, it expands to become a red giant. At this stage, the star is cooler and is now fusing helium into carbon at its core. The next stage the star moves to is determined by its mass. For low-mass stars like our Sun, the core collapses once the helium runs out and the outer shells of the star are expelled to form a planetary nebula. The core is left behind as a white dwarf which eventually turns into a black dwarf. For a high-mass star (~10 time the mass of our Sun), the star undergoes a supernova explosion. Then the remnants will either form a neutron star if they are 1.4 to 3 times the mass of our Sun or a black hole if they are more than 3 times the mass of our Sun.
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