Physics Dept. Demonstration Manual

DLD03 - Inertia Sphere, Breaking Thread


To demonstrate the inertia of a body at rest or in motion.

  • Inertia ball
  • Stand and 3-finger clamp
  • Pre-cut string, with Bowlines at ends
  • Hammer, small (nylon, reverse woven)
  • Absorber


Inertia ball is suspended on the string. The second section of string is attached to the lower end of the ball. The hammer is attached to the lower free end.

  1. With a steady pull, the top supporting string breaks.

  2. With a quick jerk, the string below the sphere breaks, due to the inertia of the sphere.