The best replacement for inertia is momentum.

The best alternatives to inertia are rated as following:
★★★★★  momentum
★★  gas shotgun
★★  mass
★★  gravity
★★  friction
★★  gas operated
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★  torque
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★  mechanical trigger
★  gas operated shotguns
  moment of inertia
  impulse
  section modulus
  centrifugal force
  kinetic energy

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Speaking about inertia, one probably shouldn't forget about torque.

Other search terms related to inertia and their ratings are:
★★★★★ torque
★★ triple integrals
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inertia
momentum
gas shotgun