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A balloon hovercraft & the CMS particle detector?!



Extended list of materials and tips:

  1. A smooth surface (glass is ideal, a table works usually fine)
  2. A CD or DVD (if you have an old one laying around)
  3. Super glue (or any glue that bonds to plastic well)
  4. A sports bottle cap (ideally, with a protruding rim)
  5. A cardboard tube
  6. A balloon

Delving a little deeper into the physics:

Our DIY hovercraft, just like the CMS detector’s feet [3], pushes air underneath it, creating pressurized air cushions which work like a wedge between the faces. The air is like a lubricant, meaning that it forms a slim film that supports the weight, which enables the hovercraft to glide parallel to a smooth surface. [2] For example, we can see the same phenomenon when we throw a playing card across the surface of a table: it slides surprisingly far. If the surface is rough or the card has holes in it, then it does not glide at all. It is an example of a hydrodynamic bearing, where the pressure is generated automatically by the movement of the sliding parts. There are also hydrostatic bearings, for which the necessary lubricating film pressure is achieved by external pressure generation. This is the case for our hovercraft, for which the pressure is generated by the flow coming from the deflating balloon. Air hockey tables or large scale hovercrafts work according to the same principle. [1]

Links for further information:

  • [1] Steve Mould, The self-levitating Kingsbury aerodynamic bearings (2020). More about hydrodynamic and hydrostatic bearings, and a cool demonstration with a syringe.
  • [2] Etienne Guyon, Jean-Pierre Hulin, Luc Petit and Catalin D. Mitescu, Physical Hydrodynamics (2015). Fluid mechanics textbook chapter on lubricated flows.
  • [3] CERN, The closing of the CMS experiment (2022). A more in-depth video about moving the CMS detector slices.