Results are out! Find what you need...fast. Get quick advice or join the chat
Hey there Sign in to join this conversationNew here? Join for free

Random Physics related question

Announcements Posted on
Got a question about Student Finance? Ask the experts this week on TSR! 14-09-2014
    • Thread Starter
    • 0 followers
    Offline

    ReputationRep:
    If a bomb went off and you are relatively close to the proximity of the detonation - BUT not close enough to be killed by the inferno / flame of the explosion - Could you be killed by the shockwave?

    random question I was contemplating.
    • 13 followers
    Offline

    ReputationRep:
    Like an ordinary wave, a shockwaves carries energy and can propagate through a medium (solid, liquid, gas or plasma) Shock waves are characterized by an abrupt, nearly discontinuous change in the characteristics of the medium.Across a shock there is always an extremely rapid rise in pressure, temperature and density of the flow. Thus, I have troth that it may, although, I may be wrong.
    • 1 follower
    Offline

    ReputationRep:
    (Original post by freedomyak)
    If a bomb went off and you are relatively close to the proximity of the detonation - BUT not close enough to be killed by the inferno / flame of the explosion - Could you be killed by the shockwave?

    random question I was contemplating.
    Yes.

    Explosives rarely kill by the chemical reaction alone, in fact that is the one method they don't kill by, because with the exception of Hydrogen bombs you will have died by another means first.

    The two main means that explosives kill are -

    1. Shrapnel and debris - lots of very fast moving bits of razor sharp metal, easily as lethal or more so than bullets, and with the added benefit of being much more likely to hit as they radiate in all directions.

    2. The shock-wave - the force hitting you if you are close by is enough to break bones, rupture internal blood vessels and knock the brain around inside the skull. May not kill instantly, but may well be fatal.
    If a shock-wave isn't sufficiently strong to kill you, it may well leave you unconscious or concuss or similarly disorientated, and likely with some injuries.

    Shrapnel is the most likely killer, then the shock-wave if you're somehow shielded from the shrapnel.
    • 0 followers
    Offline

    ReputationRep:
    Im not OP, but are shockwaves basically air moving really fast from the explosion? Like wind?
    • 1 follower
    Offline

    ReputationRep:
    (Original post by DonWorryJockIsHere)
    Im not OP, but are shockwaves basically air moving really fast from the explosion? Like wind?
    Pressure waves in fact. Wind actually displaces the air permanently, but as a shock-wave passes the air moves away, then back, and returns to its original position. (it will move a bit after because the explosion created extra gas, but that will be slower than the shock-wave)

    The force you would feel is because the wave is near-discontinuous, so you have a sharp spike in pressure at the front of your body with normal air pressure at the back, and this mismatch produces a force which throws you backwards.

    Effectively it's the same physics as sound, just in a rather more abrupt, forceful form.
    • 0 followers
    Offline

    ReputationRep:
    (Original post by The Mr Z)
    Pressure waves in fact. Wind actually displaces the air permanently, but as a shock-wave passes the air moves away, then back, and returns to its original position. (it will move a bit after because the explosion created extra gas, but that will be slower than the shock-wave)

    The force you would feel is because the wave is near-discontinuous, so you have a sharp spike in pressure at the front of your body with normal air pressure at the back, and this mismatch produces a force which throws you backwards.

    Effectively it's the same physics as sound, just in a rather more abrupt, forceful form.
    Oh wow thats really intersting, would you be able to survive a shockwave then, if you hid behind a wall? you would not be able to feel anything?

    And also, suppose that two bombs went off and produced separate pressure waves that were travelling in opposite directions. Assuming the waves were coherent and in phase would it be possible to get constructive interference and produce an even bigger 'shockwave' when they cross?
    • 1 follower
    Offline

    ReputationRep:
    (Original post by DonWorryJockIsHere)
    Oh wow thats really intersting, would you be able to survive a shockwave then, if you hid behind a wall? you would not be able to feel anything?

    And also, suppose that two bombs went off and produced separate pressure waves that were travelling in opposite directions. Assuming the waves were coherent and in phase would it be possible to get constructive interference and produce an even bigger 'shockwave' when they cross?
    You'd still feel something.

    Being a wave, effectively the same as sound, the shockwave is able to both diffract around walls and also pass through the solid.

    However, as a shock-wave consists of many different frequencies, different parts would diffract or pass through different amounts, so a lot of energy would be dissipated. It would be less powerful. Providing the wall survives.

    Interference could occur between two shockwaves, but again because of the range of frequencies involved it would not look like a normal standing wave. At the moment they meet you would get a very high-pressure point, but this would not last as the different frequencies will only all be in-phase at one point.

    Also shockwaves are characterised by having much higher pressure on one side of a small volume than the other, whereas if two met then both sides would have the same, high pressure. The result would be a crushing force, not the push shockwaves normally are associated with.

    It's not right to talk about shock-waves as having a single, well defined phase, because they consist of an infinite range of frequencies. At the boundary, all these components are in phase for a brief time, but at any other point or time they are in a random phase distribution creating no overall effect.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: April 20, 2012
New on TSR

Writing your personal statement

Our free PS builder tool makes it easy

Article updates
Reputation gems:
You get these gems as you gain rep from other members for making good contributions and giving helpful advice.