Imagine this theoretical problem—you try to push a block on a horizontal, frictionless surface in a region of space that is free from gravity. It will still require some effort to move the block (i.e., change its motion). It is the mass of the block alone that makes it necessary to exert a force to change its motion. This mass is its inertial mass. How does this mass compare with its gravitational mass? With this apparatus, students will measure the periodic motion of the two blades in the inertial balance and identify the role gravity plays in its operation. Students will then determine the relationship between gravitational mass and inertial mass. Newton would be proud of them!