OCR - P6: Matter – models and explanations

P6.5 How can scientific models help us understand the Big Bang? (separate science only)
Background to the topic What you should be able to do:

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.

2. Explain, for the circular orbits, how the force of gravity can lead to changing velocity of a planet but unchanged speed

3. Explain how, for a stable orbit, the radius must change if this speed changes qualitative only

4. Recall that the solar system was formed from dust and gas drawn together by gravity

5. Use the particle model of matter to explain how doing work on a gas can increase its temperature (e.g. bicycle pump, in stars)

6. Explain how the Sun was formed when collapsing cloud of dust and gas resulted in fusion reactions, leading to an equilibrium between gravitational collapse and expansion due to the fusion energy

7. Explain the red-shift of light from galaxies which are receding qualitative only

8. Explain that the relationship between the distance of each galaxy and its speed is evidence of an expanding universe model

9. Explain how the evidence of an expanding universe leads to the 'Big Bang' model