One of these devices named for Persoz can measure 
One of these devices named for Persoz can measure a sample's hardness. The double type of this object is a classic example of chaotic behavior. A useful approximation when working with these objects involves assuming that "sin theta equals theta." These objects have period approximately equal to "two pi times the square root of quantity length over gravitational acceleration." These devices exhibit simple harmonic motion, and one of these was used to show the rotation of the earth by Leon Foucault. For 10 points, name these devices consisting of a weight suspended from a pivot.
One of these devices named for Persoz can measure a sample's hardness.
{pendulums}