An inertial propulsion engine, or inertia drive, is any one of a class of devices that purport to produce a linear motion with no net momentum exchange. Invariably the devices fail to operate under controlled conditions, and are found to rely on a non-linear effect of the supports they sit on. Classic examples include devices that inch along a tabletop or when floating in water, but stop working once they are suspended or in vacuum.
There are hundreds of such devices, but typical components include either vibational or rotating masses, in which one portion of the cyclical motion is high-speed, and the other low-speed, or alternately high and low impulse. The result is that for some of the motion there is a high force being generated, enough to overcome friction. However on the "return stroke" the force is not high enough, and any motion occurring in the first portion is not reset. In this way the devices "steal" working mass from their supporting surface, a fact that may not be apparent to casual observation. Another class of similar devices uses interaction with the air in a similar manner. As such they are physically uninteresting, as wheels and propellors are far more efficient ways of moving a vehicle in reaction to air or ground.
In most cases the devices in question are supported by a single inventor who claims they are on the brink of solving all of the world's problems, as soon as someone takes them seriously. Invariably when the device fails in a controlled test, "big science" is blamed for the failure.
Examples of IPE's:
- Henry Bull's Impulse Engine
- Thornson Inertial Engine
- Cook Inertial Propulsion Engine
