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I remember watching a few years ago, a show on YouTube called "Is It A Good Idea To Microwave This?" The presenters regularly placed everyday items in a microwave and observed what happened.

Episode 167 - Airbag (YouTube)

On one episode, they place a car airbag inside the microwave and started it. Within a few seconds, it activated and blew the door of the microwave many feet away while almost injuring them.

My question is, how did the microwave activate without any physical shock? I was under the impression that airbags activate when sensors are triggered in a car crash by force. But in this case, there was no force, only microwave energy.

Could someone with a better understanding of physics please explain this?

Eric Hernandez
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  • "it activated and blew the door of the microwave many feet away while almost injuring them." Darwinian evolution isn't 100% repeatable. That attempt at demonstrating how it works failed. – alephzero Jun 25 '21 at 19:37

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how did the microwave activate without any physical shock? I was under the impression that airbags activate when sensors are triggered in a car crash by force.

That's only true when the airbag is used as part of a larger system.

An airbag inflator itself is a pyrotechnic device. It's activated by heating an "ignitor" that initiates a chemical reaction that propagates through a mass of propellant at high speed to create the gas that inflates the bag. The "shock sensors" (accelerometers) that you speak of are part of an electronic system that continually monitors conditions in the car (including, speed, acceleration, and whether or not there is somebody sitting in the seat). It's the electronic system that decides if and when it's time to fire the "ignitor" that initiates the air bag deployment.

The microwave energy may have created a spark somewhere within the inflator that initiated the chemical reaction, or it may have heated some metal part hot enough to initiate it.

Solomon Slow
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  • I was thinking more that the microwave induced a current on the igniter - nice little wires make good microwave antennas. – Jon Custer Jun 25 '21 at 12:43
  • @JonCuster that's a possibility, given that I've been able to generate sparks on a dish with a metal rim (ceramic plate) in a home microwave oven. – Carl Witthoft Jun 25 '21 at 12:46