PURPOSE: To show the formation of a crater from a meteor and to discuss craters.
DESCRIPTION: A box holds dry sea sand covered with a fine layer of cocoa powder, as shown above. One tosses small ball bearings into the sand to form craters. The craters can be either elliptical or round, depending on the angle that you toss it. And the craters are always much larger than the 'meteor' ball bearing that formed it. This demo can be used to point out why its craters are not like craters from actual meteors traveling near the speed of sound.
The craters that are formed by this demo are much larger in size than the size of the small 'meteor', as shown in the right photo above. This is because you cannot easily throw something at the speed of a shockwave, which is at or above the speed of sound in sand. A real meteor travels at speeds near or greater than the speed of a shockwave in sand, so the crater from a real meteor is always about the same size as the meteor that formed it. And a real meteor always makes a round crater, never an elliptical one, as shown in the lower right hand corner of the right photo.
EQUIPMENT: Sand box, as photographed. It is effective to present this demo with a video camera and projector.
SETUP NOTES: 1/2 hour.
Deep Impact: The Physics of Asteroid/Earth Collisions
Donald Metz and Arthur Stinner
Phys. Teach. 40, 487 (2002)