Task: Text Categorization
Input (English): This law can be written in the Voigt notation as a six by six compliance matrix. One form of this law is the expression for the free energy of a deformed isotropic body, and includes the Lam coefficients. A generalization of it includes Young's modulus, and simple harmonic motion occurs when it is obeyed. This law includes a negative sign because the force exerted is always directed opposite to the displacement of the object. FTP name this law that governs springs and is stated as F equals negative k times x.
Output (English): Science