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By James Dacey
When you think of cutting-edge experimental physics, you might picture the grandiose detectors of the Large Hadron Collider (LHC), or perhaps a lab-coat-wearing scientist hunched over a shiny new microscope. Sometimes, however, all you need is a bucket of sand, a balloon and a pin.
That is what we discovered on a recent trip to a physics lab at the Benemérita Universidad Autónoma de Puebla (BUAP) in Mexico. Researcher Felipe Pacheco Vázquez treated us to a quick demo of how craters form as a result of an explosion in a pressurized air cavity in a sand bed. These holes in the ground have different characteristics from the craters caused by something big from space smashing into the Earth.
See the video above to see Pacheco Vázquez give a quick demonstration of the process to Physics World editor Matin Durrani. Those of you interested in learning how to handle sharp objects in a safe fashion would be advised to give the video a skip!
This week, Pacheco Vázquez and his colleagues have published a report of their research in Physical Review Letters. Their findings could help to identify the origin of planetary craters and to understand the evolution of planetary terrains. To be fair, the experiments described in this published study require a bit more equipment – including a high-speed camera, a hosepipe and an air gun. Nothing excessively fancy though.
Matin and I were in Mexico on a fact-finding mission for a special report on the country, which will be available on this website in September.
It is normal that the explosion of a cavity under an “appropriate pressure” will lead to a crater. We often see huge and quite deep craters after the explosion of a bomb even at the surface of the ground.
Yes, something interesting is that the crater is always circular independently of the cavity shape if the cavity is located deep enough inside the sand. You can try with rectangular, trinagular, square-shaped, you always get a circular rim if a critical depth is considered.
The crater is always circular, because of the outwards isotropic(spherically symmetric) high pressure exerted by the the explosion point.