When they said that
It was when you ignore loss of Energy,
In Real life you have Air resistance dude to which you lose Energy,
But if you don't have that Loss, The Pendulum will continue forever... Because of First Law of Motion
Anyways I got an Idea for you
You should do an experiment where you see how much energy , Here is how its mentioned in our textbook
The total energy of the bob of a simple pendulum executing simple harmonic motion, :
OR ANOTHER WAY HERE :
Setup :
You also need a stopwatch
Procedure :
Set the Pendulum to oscillate with suitable amplitude, and simultaneously start the stopwatch (make sure to get one)
Note down the Amplitude after every one minute
Observation Table :
Why A
2 -> Because if you plot a Graph of A2 vs T, You'll get it
Theory : The Energy of a Particle performing SHM is given as :
Which means E is Directly proportional to A square
Hope It helped ,
Regards