Pendulums are easy to make and fun to play with. All you need
is a piece of string, a weight to fasten to its end, and a clock
that gives you seconds.

The thing to know about pendulums is that the length of time it
takes for a one complete swing depends almost entirely on the length
of the string. At least, this true if you stay on the earth. Times
will vary on other planets because they have different gravity.
Keep this in mind on your next trip to Mars.

Enter your string length, then select a location
Length in inches
Select location Mercury Venus Earth The Moon Mars Jupiter Saturn Uranus Neptune Pluto

The period of your pendulum is