**PURPOSE: **To illustrate the measurement of inertial mass using SHM.

**DESCRIPTION: **A mass is placed on the platform and set into motion, executing SHM horizontally. The period of the oscillation T = (1/2 pi) SQRT ((M=m)/k), where M is the mass of the platform and m is the unknown mass. Making period measurements with and without the unknown mass m one can determine its inertial mass.

**SUGGESTIONS: **

**REFERENCES: ** (PIRA 1F10.11) See Demonstration Reference File for article discussing the difference between inertial mass and gravitational mass.

**EQUIPMENT: **Inertia balance, 500g, two 200g, and 100g masses, unknown mass, and digital timer.

**SETUP TIME: **None.