The gravitational interaction between the planets and the Sun keeps the planets in (almost) circular orbits around the Sun, all in the same direction.
Similarly, it is the gravitational interaction between a planet and its moons or artificial satellites that keeps them in orbit.
The force needed to keep an object moving in a circle depends on the speed of the object and the radius of the circle.
The greater the speed and/or the smaller the radius, the greater the force needed.
If a satellite or planet slows down, it will be pulled in to a smaller radius orbit.
The solar system was formed over long periods from clouds of gases and dust drawn together by the force of gravity.
When a force is used to compress a gas, work is done on the gas, leading to an increase in temperature.
During the formation of a star such as the Sun, a cloud of gas is pulled together by gravity, its temperature increases and the hydrogen nuclei gain sufficient energy to fuse into helium nuclei, releasing more energy.
The Universe contains thousands of millions of galaxies.
The light coming from distant galaxies shows a red-shift that suggests that distant galaxies are moving away from us.
The further away a galaxy is, the faster it is moving away from us; this suggests that space itself is expanding.
Scientists' explanation for these observations is that the Universe began with a 'Big Bang' about 14 thousand million years ago.
The acceptance of the 'Big Bang' model to describe the early stages of the Universe depends on the interpretation of observations, as more observations were made, the theory became more secure.
Telescope designs have improved over the last 100 years, and modifications have made it possible to observe regions of the electromagnetic spectrum other than visible light.
Placing these instruments outside the atmosphere has improved the range and quality of data obtained, and these improved data have increased the confidence in the 'Big Bang' model. |
1. Recall the main features of our solar system, including the similarities and distinctions between the planets, their moons, and artificial satellites
Nuclear fusion in stars
In your practical work you will have investigated the relationship between the force, speed and radius of path for an object moving in a circle.
You will discuss the development of the 'Big Bang' model of the beginning of the Universe as an example to understand how scientific explanations become widely accepted. |
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