tom swift among the diamond makers

 pendulums are amazing things. but kind of hard to understand first you must know that the pendulum is technically a weight attached to a bar. so it is free to swing these 2 girls make a pendulum and figure that every time you pull the weight back .let it goes it always comes back to the place it used to be from where it started. and then they attached another weight but this is just a cork. and it still does the same amount of swings in another it doesn't matter about the weights. they will stay the same amount of swings and it doesn't matter about the speed. they will always have the same speed and the same amount of swings.