2. Chu Wai Kit Regional Support Section, Information Systems Division, Education Department, HK.

3. Gunpowder and firework were invented and used by the Chinese in the 14th century. Later the gunpowder was tranferred to Europe and was widely used in wars from 15th century onwards.

4. Where will it hit? Although the guns were improved and became bigger and bigger, the problem of calculating the hit position was not solved.

5. The famous Greek philosopher Aristotle (384 B.C.) believes the path should follow two straight lines.

6. Later his idea was revised and an arc was inserted in between the straight lines. The path was “found” by geometric construction.

7. There was no breakthrough until Galileo Galilei (A.D. 1564) put forward his explanation base on concept of forces. The hit position can be predicted accurately.

8. Issac Newton (A.D.1642) further developed Galileo’s work. He suggested as a very fast shell falls down due to gravitational force, it may follow the curvature of the Earth and keeps flying above the ground.

9. Galileo was great in calculating the hit position. Newton was great to predict a shell never hits and moves around the Earth if it is fast enough. This is proved by satellites 300 years later.