Impact Cratering notes

(draft 10/8/98)

Elizabeth E. Roettger, interpreting and synthesizing a standard activity from many sources.

Description: Participants drop objects into a grainy or powdery surface to simulate impact crators on various worlds in our Solar System.

This activity can be adapted for almost any age group or level of sophistication.

Possible Objectives

Participants will:

create and measure "craters" from three different impactors
create and measure "craters" from one impactor at three different energies (heights)
Examine other aspects of cratering, such as fluffiness of the medium, texture, angle of impact, and possibly non-powdery medium.

Materials/equipment (see other page for details and options):

Container (large bowl, tub, or box) for each team
Surface medium (sand or flour are fairly common)
Three impactors of different sizes and/or different densities (rocks, marbles, and steel balls are fairly common choices)
Surface coloring medium (cocoa powder is common; use shaker, sifter, or strainer to distribute)
Ruler
Optional: object retriever (magnet or pickle-grabber), slingshot or other means of adding energy to the impact, dropcloth
Optional: movie camera or regular camera and strong directional light source

Preparation:

1. Spread the drop cloth, if using. Fill the container to at least 1 inch (deeper is often better) with the surface medium.

2. Optional: pack the surface medium, perhaps smooth the surface, perhaps remove large lumps.

3. Lightly coat the surface medium with a powder of a contrasting color, so that any debris that is thrown out of the crater will be easily visible.

Procedure:

0. Look at images of impact craters on our Moon and other places in our Solar System.

1. In turn, drop each of the three impactors from a known height. With typical surface media, shoulder-height is a good starting point.

2. After each impact, measure the crater. I suggest measuring the diameter of the crater rim (in several directions if it is not round), the ejecta blanket (stuff that shoots out and lands on surface) - again several measurements may be appropriate, and the depth of the crater. HOWEVER, I strongly suggest making as many measurements as possible BEFORE removing the impactor(s). If the container is large enough, do three craters before removing the impactors. This also allows participants to see the effect of overlapping impacts. You may wish to photograph the results (put a ruler in the photo and light it at an angle for best effect), or film the actual impacts (in slow motion, this can be very impressive).

3. Retrieve the impactor that gave the most satisfying results. If needed, re-set the medium and re-coat with a contrasting color.

4. Drop the SAME impactor (or identical impactors, if available) from three different heights. The best heights depend a lot on the medium and impactor, but standing on a chair to achieve the highest is often quite effective. Measure as you go.

5. Compare the impacts. What affects the size and quality of the craters? Do more experiments as needed to check your answers. (I usually ask participants to look at one more characteristic - packing, angle of impact, medium, whatever they like. This can give some very creative and interesting results.)

6. Share your results with other teams. Compare your theories about what makes impacts different. Are your impacts different from the natural ones, in any aspect other than size?

Attributed, non-commercial distribution of these notes is encouraged. Comments and suggestions are appreciated.

Web version 8 November 1998
by Elizabeth E. Roettger.
URL: http://nthelp.com/eer/HOAimpact.htm