# Questions about shock waves from explosions and impacts

#### autodidude

1) How does an explosion or impact (e.g. meteorite) create a pressure wave? In the case of a meteor, if kinetic energy is being transferred into the wave, how does this conversion take place?

2) Is it the shock wave from an explosion or impact (e.g. meteorite) just the collision of air molecules as they bumping into each other and transferring the energy? How does the explosion/impact cause this (in meteorite case, I suppose it's mostly the kinetic energy that's transformed, but how does that happen?)

3) How does this kill or maim you? What happens on a molecular level?

4) In a car accident, how does the force/energy hurt you (especially if the vehicle has no crumple zone)?

Thank you

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#### davenn

Science Advisor
Gold Member
a dictionary definition...
(Physics / General Physics) -- a region across which there is a rapid pressure, temperature, and density rise, usually caused by a body moving supersonically in a gas or by a detonation

Wikipedia entry -- A shock wave (also called shock front or simply "shock") is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or in some cases in the absence of a material medium, through a field such as the electromagnetic field. Shock waves are characterized by an abrupt, nearly discontinuous change in the characteristics of the medium.[1] Across a shock there is always an extremely rapid rise in pressure, temperature and density of the flow. In supersonic flows, expansion is achieved through an expansion fan. A shock wave travels through most media at a higher speed than an ordinary wave.

Im sure others will add more comments :)

Dave

#### Drakkith

Staff Emeritus
Science Advisor
2018 Award
1) How does an explosion or impact (e.g. meteorite) create a pressure wave? In the case of a meteor, if kinetic energy is being transferred into the wave, how does this conversion take place?
The meteor impacts air molecules and transfers kinetic energy to them. These then impact other air molecules and so forth.

2) I suppose it's mostly the kinetic energy that's transformed, but how does that happen?)
Not sure what you mean by "How".

3) How does this kill or maim you? What happens on a molecular level?
The impact of the molecules in the shock wave exert enough force to break the bonds of the molecules in your body.

4) In a car accident, how does the force/energy hurt you (especially if the vehicle has no crumple zone)?

Thank you
The primary effect is that your body is decelerated at a very high rate. A modern vehicle is designed to absorb and dissipate energy over the course of the accident. This, and the addition of things like seat belts and air bags, causes your body to decelerate slower. So instead of your face crashing into the hard steering wheel at 70 mph and decelerating to 0 in a small fraction of a second, the seat belt and air bags cause you to take a much longer amount of time to decelerate. So instead of your brain hitting the front of your skull at 70 mph, which may kill you, it is greatly reduced.

#### autodidude

1) So, basically the molecules are hitting each other at a very high speed?

2) I mean how kinetic energy is transferred into the medium, if that makes sense

3) So when the wave hits you, it's the molecules hit yours with a lot of force?

4) What if you were completely strapped down so that none of your body parts could go flailing?

#### Drakkith

Staff Emeritus
Science Advisor
2018 Award
1) So, basically the molecules are hitting each other at a very high speed?
Yep. Note that MOST explosions are accompanied by large amounts of shrapnel which work just like bullets.

2) I mean how kinetic energy is transferred into the medium, if that makes sense
By the force of whatever is hitting the molecules and atoms in the medium. The interactions between atoms and moleucles are governed by the Electromagnetic force until you get into extremely high energies far beyond what a normal explosive would be.

3) So when the wave hits you, it's the molecules hit yours with a lot of force?
Technically I think it should be called kinetic energy and momentum.

4) What if you were completely strapped down so that none of your body parts could go flailing?
Depends on what you were strapped down with. If it were cables made of extremely strong metal that didn't give at all it would be almost as bad as impacting part of the vehicle. Remember that YOU have to slow down as well as the car in an accident. The longer it takes you to slow down the less g-force your body experiences. This is a simplification, as other things come into effect, but thats the basics.

Have you ever ridden a roller coaster at a theme park? At the end of the ride you typically brake very hard for a couple of seconds and your body wants to go flying forward. Imagine if instead of taking 2-3 seconds, it took 1/10th of a second. You would probably not survive, at least not without some pretty bad injuries.

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