One reversible type of this object is named after Henry Kater, while one of them named after Persoz can be used to measure hardness.   
One reversible type of this object is named after Henry Kater, while one of them named after Persoz can be used to measure hardness.   The equation of motion of the simplest type of these objects can be solved by using Jacobi elliptic functions, while the double one of them is a famous example of a system displaying chaotic behavior.  A physical one's motion depends on the value of its moment of inertia about its pivot point, while the simple one's equation of motion is often simplified by making the sine of theta = theta small angle approximation, in which case it exhibits simple harmonic motion. FTP, name these oscilatting devices, one of which was used to demonstrate the rotation of the Earth by Foucault.
One reversible type of this object is named after Henry Kater, while one of them named after Persoz can be used to measure hardness.   
{pendulum}