Solar System And Orbital Motion
Visão Geral
Somewhere on the wall of a building near you there is a satellite dish, bolted into the brickwork, pointing at an empty patch of sky. Nobody adjusts it. Nobody tracks anything with it. It was aimed once, on the day it was fitted, and it has not moved since, and the pictures keep arriving. That only works because a machine the size of a minibus, thirty six thousand kilometres above the equator, is circling the planet at a speed chosen so precisely that from the ground it appears to be nailed in place.
This lesson takes an inventory of the solar system and teaches you to separate a planet from a moon, a dwarf planet from an asteroid and either of those from a comet, on size and on the way each one moves. It steps back to the galaxy and then to the universe, sorts natural satellites from artificial ones, and sets the two orbits an engineer can choose between against the jobs they suit. Then it goes after the mechanics: what actually holds a satellite up, why an object going round a circle at a steady speed is nevertheless accelerating every second of the journey, and why a satellite close in is racing while one far out is dawdling. That second half is Extension Tier material, and this lesson marks it clearly, so you always know which parts of the topic your own paper will ask for.
Objetivos
- The Earth is one of eight planets orbiting the Sun (a medium sized star), which together with other smaller objects (asteroids, dwarf planets, comets) and moons orbiting several planets, make up the solar system. Students should be able to describe the principal differences between planets, moons, the Sun, comets and asteroids in terms of relative size and motion.
- Our universe is made up of: thousands of millions of galaxies that are each made up of thousands of millions of stars; our Sun is one of thousands of millions of stars in our galaxy called the Milky Way.
- Planets orbit the Sun and a moon is a natural satellite of a planet. Artificial satellites orbit the Earth and can be in geostationary or low polar orbits.
- Gravity provides the centripetal force that keeps planets and satellites (both natural and artificial) in orbit.
- The force of gravity acts towards the centre of the orbit. This unbalanced force causes acceleration towards the centre of the orbit, changing the direction of motion of the body (its velocity) but not its speed. The equation for calculating centripetal force is not required.
- The centripetal force due to gravity decreases as the separation of orbiting masses increases, resulting in lower orbital speeds.
- At a particular separation of the masses, the centripetal force results in a particular orbital speed. To stay in a stable orbit at a particular distance, the planet or satellite moves at a particular speed. A change in orbital speed results in a change in orbital radius. Students should be able to explain the motion of moons and artificial satellites and be able to apply this to the design of satellite placing where the speed will determine the radius of the satellite’s final position.
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Nota de Aula
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- Which of these objects orbits a planet rather than orbiting the Sun directly? A. A comet B. An asteroid C. A moon D. A dwarf planet Answer: C
- What provides the centripetal force that keeps the Earth in orbit around the Sun? A. Friction B. Gravity C. Magnetism D. Air resistance Answer: B
- Starting with the smallest, which list puts these in order of increasing size? A. Earth, Sun, Milky Way, Universe B. Sun, Earth, Universe, Milky Way C. Earth, Milky Way, Sun, Universe D. Milky Way, Universe, Earth, Sun Answer: A
- A satellite moves around a circular orbit at a constant speed. Which quantity is changing? A. Its mass B. Its speed C. Its velocity D. Its distance from the centre of the orbit Answer: C
- Satellite X orbits the Earth at a radius of 7.0 x 10^6 m and satellite Y at a radius of 4.2 x 10^7 m. Which statement is correct? A. X travels faster than Y and takes less time for one orbit B. Y travels faster than X and takes less time for one orbit C. X and Y travel at the same speed D. X travels more slowly than Y and takes more time for one orbit Answer: A
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