Meter Based on Seconds Pendulum

This section introduces an old definition of 'meter' which uses a seconds pendulum. A 'meter' is the length of a seconds pendulum, which swings a full cycle in 2 seconds in small angles.

The French National Assembly also accepted another definition of 'meter' to be "the length of a pendulum with a half-period of one second" in year 1790.

This definition is based on the factor that a small angle pendulum with a half-period of one second will have a length of about one meter, as illustrated in the picture below:

Since "meter" is defined more accurately now with the speed of light, the accurate length of a seconds pendulum at the sea level is 0.994 meter.

With this knowledge, you can acutually create your own 1 meter string as a measuring tape.

• Get a long thing string and tie a small rock at one end.
• Hold the other end of the string and lift the rock in the air.
• Push the rock to let it swing freely in small angles.
• Using a stop watch to count the number of seconds it takes to swing 10 full cycles. One fule cycle is a forward swing and a backward swing.
• Adjust the holing position of the string until you count 20 seconds for 10 full swing cycles.
• Stop the swing. The distance between the holding position and the center of the rock is 1 meter.
• Cut extra parts of the string and you get a 1-meter string.

Last update: 2014.