The Gauss gun (often called a Gauss rifle or Gauss cannon) is a device that uses permanent magnets and the physics of the Newton's cradle to accelerate a projectile. Gauss guns are distinct from and predate coil guns, although many works of science fiction (and occasionally educators) have confused the two. Typical use of the Gauss rifle is to demonstrate the effects of energy and momentum transfer, however, self-assembling microbots based on the principle have been proposed for tissue penetration.