Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Minimum speed of an explosion

  1. Dec 23, 2003 #1


    User Avatar

    How slow can an explosion possibly be?
  2. jcsd
  3. Dec 23, 2003 #2
    I'm not sure whether there is an accurate/helpful answer to your question as it is stated. The term explosion is very general as it applies to the release of mechanical, chemical, or nuclear energy (however Feynman once stated that nuclear bombs are really electrical bombs: it's true).

    If you are referring to high explosives, there is a term you should read into: (VOD) or Velocity Of Detonation. VOD is defined as the rate at which the detonation wave travels through the explosive product. It usually falls in the rage of 2000-8000 m/s. VOD only pertains to high explosives and really has no usefull meaning in the context of low explosives. Remember that high explosives don't involve combustion reactions (oxidation reduction reactions) but rather detonation (a type of molecular dissassociation).

    Some reading:

    The Explosives and Weapons Forum.
    This site represents is a VERY competent forum community. I highly reccomend its material.

    BTW. Please be responsible with this information. I would hate to see an obituaries section added to PF.

    Edit - Grammar
    Last edited: Dec 23, 2003
  4. Dec 23, 2003 #3


    User Avatar
    Science Advisor

    I think the generally accepted difference between "detonation" and "combustion" is wether the reaction takes place at supersonic speed for the medium being burned.

    In an internal combustion engine, for example, care is taken to avoid a feul/O2/pressure combination that will "detonate" the fuel in the cylinder, because such an explosion will damage the piston heads (this is one of the main engineering obsticals to Pulse Detonation Engines). Although I've never seen it explicitly stated, the difference between detonation and combustion is always discussed in terms of a supersonic or a subsonic shockwave.

    For example, http://www.popsci.com/popsci/aviation/article/0,12543,473272-2,00.html no pulse detonation states that...


    Not a clear-cut definition, as most people would refer to what goes on inside an engine cylinder as an "explosion".
    Last edited by a moderator: Apr 20, 2017
  5. Dec 23, 2003 #4
    Thanks for catching my mistake.

    As you said. The wavefront seems to be the key factor in HE.
    It's funny though how many high explosives will not detonate without a sufficiently energetic shock wave. They are not combustible in the usual sense of the word. Even when they are exposed to intense flame many types remain stable and will not detonate or will not do so efficiently. The oxidation (for most HE) occurs only after the molecules have been "cracked open."
    Also HE usially carries mos of its own oxidizer in the compund.

    On a side note: I really do hate changing those head gaskets after a bad tank of fuel.
    Last edited: Dec 23, 2003
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook