where f is the frequency in hertz, T is the tension in kilogram meters per second squared (newtons), u is the mass per unit length of the string in kilograms per meter, and l is the vibrating ...where f is the frequency in hertz, T is the tension in kilogram meters per second squared (newtons), u is the mass per unit length of the string in kilograms per meter, and l is the vibrating length of the string in meters. In this experiment, the tension, T, is simply the product of a suspended mass (kilograms) times the acceleration due to gravity (9.8 meters per second squared).