The Law of Universal Gravitation

In ancient times, people believed that the Earth was the centre of the solar system and tried to understand and explain the movement of the Sun, the Moon, the stars and the planets around the Earth. As scientific knowledge and technology improved over time, this idea (called the geocentric theory, from the ancient Greek words meaning Earth-centred) lost favour and new theories about the solar system were put forward.

Tycho Brahe (1546-1601) and Galileo (1564-1642) made accurate measurements of the heavens, which were the basis for later theories. Nicolas Copernicus (1473-1543) believed that the Earth was not the centre of the solar system but

just another planet revolving around the Sun, which itself never moved. This type of theory was called heliocentric. Johannes Kepler (1571-1630), an assistant to Brahe, used Brahe's measurements to support Copernicus' heliocentric theory. This led to his discovery of three laws relating to planetary movement, including the fact that the planets move in elliptical orbits around the Sun.

It was left to Isaac Newton to expand on these theories by testing and proving Kepler's laws. By observing things around him, Newton realised several things. One was that objects can be in one place, without moving. This is called inertia. Then, if the object moved, it moved toward another object. The phenomenon causing this pull of one object towards another was the force of gravity (or little g). Newton found that the mass of the two objects and the distance between them determined the strength of the force of gravity and developed an equation which expressed this relationship.

Continuing to test and expand his findings, Newton hypothesised that this relationship existed not only between objects on the Earth but also objects in space. This led in 1687 to Newton's Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy, usually called Principia) in which he wrote about his historic discovery of the Law of Universal Gravitation (or big G). By calling his discovery a la=w, it meant that the relationships he had discovered were true everywhere and in all cases.

Newton's discovery had a huge impact on scientific thinking for centuries afterwards. In fact, his findings were not improved upon until 1905, when Albert Einstein introduced his Special Theory of Relativity.

1. What were the theories about solar system?
2. When were these theories put forward?
3. What did Copernicus believe in?
4. What supported Copernicus' heliocentric theory?
5. What was left to Newton?
6. What is inertia?
7. What is the force of gravity?
8. What equation did Newton develop?
9. Why did Newton call his discovery a law?
10. Who improved Newton's findings? When and how?

1. people believed that the Earth was the centre of the solar system and tried to understand and explain the movement of the Sun, the Moon, the stars and the planets around the Earth.

2. Aprocsimatelly in 1503—1512 Copernicus was speeded his ideas.

3. Nicolas Copernicus (1473-1543) believed that the Earth was not the centre of the solar system

4. Brahe's measurements was supported Copernicus' heliocentric theory

5. three laws relating to planetary movement, including the fact that the planets move in elliptical orbits around the Sun.

6. inertia mean that objects can be in one place, without moving

7.it is force between two objects

8. Newton found that the mass of the two objects and the distance between them determined the strength of the force of gravity

9. Newton called Mathematical Principles of Natural Philosophy la=w.

10. Albert Einstein in 1905 improved Newton's findings. He improved this theory for high speeds.

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