Imagine you are working on a project "The evolution of clocks".
Read the text and answer the questions:
What caused the invention of a pendulum? Was it an important invention? Why/why not?
In the old days people told the time by the size of the shadow cast on the ground by a post. Sundials which developed from this primitive method are used as decorations in the gardens today.
A burning rope with knots at regular intervals was another ancient method of telling the time. It took the fire the same amount of time to reach each knot.
One more method of telling the time was a sand glass measuring minutes, hours, etc., by the amount of time it took the sand to run into the lower glass.
Water clocks work in a similar way, using water instead of sand.
Later mechanical clocks were made, but the first ones kept time so badly that it was not worth putting a minute-hand on them.
Galileo, the great scientist, born 400 years ago, showed what a perfect timekeeper a pendulum was. So, clocks were controlled by a pendulum and they were correct to a second.
You can try making a pendulum. Tie a piece of cotton, two feet long, to a big button. Let it hang from a table while you hold down the other end of the cotton with a book.
Start swinging the cotton and look at the second hand of a watch to see how long it takes to do twenty movements. Do this with small swings, then with bigger ones.
You will find almost no difference in time. Big swing or small, it takes the pendulum the same amount of time. That is why the pendulum is used to control the speed at which the wheels of the clock go round.