Worlds in Collision

Table of Contents

Objective
Introduction
Materials
Procedure
Questions
Examples
Home

Objective:

Produce craters in sand to illustrate the cratering process in the solar system. Discover what determines the size of a crater.

Introduction

Craters are circular depressions seen on the moon, on all of the inner planets, and on moons and asteroids throughout the solar system. Craters are caused by collisions between objects within the solar system. Asteroids, meteoroids, and comets collide with planets and moons and did so much more frequnetly when the solar system was young. A recent example of this was the collision between Comet Shoemaker-Levy 9 and the planet Jupiter in July of 1994. Craters tell us much about the history of these moons and planets. New surfaces, formed by the flow of rock or ice, have few craters while the oldest surfaces are completely covered by craters.

Materials:

• A bucket or tub of fine, dry sand. (Flour is too fine, sugar and salt are too coarse. Sand of the right consistency is often sold in craft and hobby stores in a variety of colors.)

• A cup of fine, dry sand of contrasting color.

• A flour sifter or salt shaker.

• Projectiles: BBs, lead fishing weights, or the like.

Procedure:

Shake the bucket or tub of sand to level it off. Put a light dusting of the contrasting colored sand over the top of the sand in the bucket using the salt shaker or sifter. Drop projectiles such as BBs or lead fishing weights from different heights and observe the craters they produce in the sand. Make note of the size and weight of the projectile and the height from which it was dropped. Measure the width of the craters from a point on the peak of the rim to a point on the rim on the opposite side of the crater.

Questions:

• Where did the projectile go? (Is it visible on the surface or has it tunnelled below the surface?)
• Is the crater the same size as the projectile? Is it larger or smaller?
• If a projectile is thrown into the sand at an angle does it produce a round crater?
• How does the size of the crater depend upon the weight of the projectile when two projectiles are dropped from the same height?
• How does the size of the crater depend upon the height from which it is dropped when the projectiles have the same weight?
• Estimate the relative volumes of the ejecta (the material ejected out of the crater) by calculating the cube of the crater diameter. Millimeters are convenient units for measuring the diameters of these craters. (Note: The actual volume is given by Volume= p D² H/12 where D is the diameter of the crater and H is its height from deepest point to crater rim. Here we will assume that the height is proportional to the diameter so the volume is proportional to D³.)
• Compare the volume of the ejecta to the energy (weight times height) of the projectile. How do they compare?

Examples of craters left in sand by BBs dropped from heights of about a meter are shown to the left.  (Click on the picture for a larger image.) The deep sand was a dark gray craft/hobby sand. This layer was dusted with a thin layer of white sand to make the craters more visible. Multiple layers of colored sand can make for very interesting craters.

Authors:

Developed by Dr. David H. Hathaway, NASA/MSFC
Converted to HTML by Clifford Schlecht, a SHARP student from Hazel Green High School

August 1998