Chu Wai Kit

1
From Shell To Satellite

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

2
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.
3
Although the guns were improved and became bigger
and bigger, the problem of calculating the hit
position was not solved.

• Where will it hit?

4
The famous Greek philosopher Aristotle (384 B.C.)
believes the path should follow two straight
lines.
5
Later his idea was revised and an arc was
inserted in between the straight lines. The path
was found by geometric construction.
6
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.
?
7
Issac Newton (A.D.1642) further developed
Galileos 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.
8
The End
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.