This resource supports any classroom study of Mars Exploration. It is especially effective used in conjunction with the following Yes I Can! Scientific Adventure:

See Yes I Can Science! Home Page for further information regarding archived, current and planned Scientific Adventures.

Purpose

To learn about the mechanics of impact cratering and the concept of kinetic energy; and to recognize the landforms associated with impact cratering.

Materials

For each student group: Sand, tray, colored sand, drop cloth, screen or flour sifter, slingshot, safety goggles(one for each student), triple beam balance, ruler, lamp, calculator

Projectiles: 4 different sizes of steel ball bearings: 4 identical ball bearings of one of the intermediate sizes, one each of the three other sizes; 3 identical sized objects with different densities (large ball bearing, marble, wood or foam ball, rubber superball)

Introduction

Impact craters are found on nearly all solid surface planets and satellites. Although this exercise simulates the impact process, it must be noted that the physical variables do not scale in a simple way to compare with full-size crater formation. In other words, this exercise is a good approximation but not the real thing.

Impact craters form when objects from space, such as asteroids, impact the surface of a planet or moon. The size of the crater formed depends on the amount of kinetic energy possessed by the impacting object. Kinetic energy (energy in motion) is defined as: KE = 1/2 (mv ² ), in which m = mass and v = velocity. Weight is related to the mass of an object. During impact the kinetic energy of the object is transferred to the target surface. Safety goggles must be worn whenever the slingshot is in use!

Procedure and Questions

Part A

Place the tray on the drop cloth. Fill the tray with sand, then smooth the surface by scraping the ruler across the sand. Sprinkle a very thin layer of the colored sand over the surface (just enough to hide the sand below) using the flour sifter. Divide the tray (target area) into four square shaped sections, using the ruler to mark shallow lines in the sand.

In one section produce a crater using the slingshot to launch an intermediate size steel ball bearing straight down (at 90 degrees, vertical) into the target surface. The slingshot should be held at arms length from sand surface (70 to 90 cm) facing straight down into the tray. Do not remove the projectiles after launch. Use the space on the following page to make a sketch of the plan (map) view and of the cross section view of the crater. Be sure to sketch the pattern of the light-colored sand around the crater. This material is called ejecta. Label the crater floor, crater wall, crater rim, and ejecta on the sketch.

1. a. Where did the ejecta come from?
   b. What would you expect to find beneath the ejecta?
   
   Sketch Area
   
   
   
   
   
   
   
   
   
   
   
   
   c. Would you expect the ejecta to be of equal thickness everywhere?
   d. What is the ejecta distribution and thickness in relation to the crater?
   
   In the next section of the target tray, produce a crater using the slingshot to launch a steel ball bearing (the same size as above) at 65 degrees to the surface. The angle can simply be estimated. The end of the slingshot should still be 70 to 90 cm from tray. Be certain no one is "down range" in case the projectile ricochets. Sketch the crater and ejecta in plan view on the space provided below.
   
   Sketch Area
   
   
   
   
   
   
   
   
   
   
   
2. Is there an obvious difference between the two craters or ejecta patterns?
   
   In the third section of the target tray, produce a crater using the slingshot to launch a steel ball bearing (the same size as above) at 45 degrees to the surface. Again, estimate the angle. The end of the slingshot should still be 70 to 90 cm from the tray. Be certain no one is "down range" in case the projectile ricochets. Sketch the crater in plan view on the space provided on the following page. As above, label the parts of the crater.
   
   Sketch Area
   
   
   
   
   
   
   
   
   
   
   
   In the fourth section of the target tray, produce a crater using the slingshot to launch a steel ball bearing (the same size as the previous exercise) at about 5 to 10 degrees to the surface. Again, estimate the angle, and make sure not to hit the rim of the tray. The end of the slingshot should still be 70 to 90 cm from tray. Be sure no one is "down range" in case the projectile ricochets. Sketch the crater in plan view and cross section on the space provided below.
   
   Sketch Area
   
   
   
   
   
   
   
   
   
   
   
   Examine the sand craters and your sketches.
3. How does ejecta distribution change with impact angle?
   Examine Figure 4.1, a photograph of the lunar crater Messier.
4. a. Was this a high angle or low angle impact?
   b. Did the meteoroid which formed Messier impact from the east or west?

Part B

Remove the four steel ball bearings from the sand tray and thoroughly mix the sand and colored sand to produce a uniform mixture. Smooth the target surface with the ruler. The remaining experiments will be performed without a colored upper layer of sand. Divide the target area into four sections as before.

• Produce four craters on the smooth target surface, using the same four identical steel ball bearing as in Part A. Find the mass of one of the projectiles before launching it and enter the value in the table below. Make the first crater by dropping the projectile from a height of 10 cm above the surface. Measure the diameter of the crater formed and enter the value in the table.
• For the second crater, drop the projectile from a height of 2 meters. Measure the crater diameter and enter it in the table.
• The third projectile should be launched with the slingshot 70 to 90 cm above the tray and with the rubber tubing pulled back slightly (extended ~3 cm). Measure the crater diameter and enter it in the table.
• For the last crater, extend the slingshot ~15 cm. The slingshot should still be 70 to 90 cm above tray. Measure the crater diameter and enter it in the table.
• Calculate the kinetic energy of each projectile and enter the values in the table.

	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
Shot 1
Shot 2
Shot 3
Shot 4

* velocities are approximate

Part C

Remove the projectiles and smooth the target surface with the ruler. Divide the target into four sections. Find the mass of each projectile and enter the values in the table below. Produce four craters by dropping 4 different sized steel ball bearings from a height of 2 meters above the target surface. Measure the crater diameter produced by each impact. Enter the projectile mass and resultant crater diameters in the table below. Calculate the kinetic energy of each projectile and enter the values in the table on the next page.

	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
Shot 1 (smallest)	6.3
Shot 2 (next larger)	6.3
Shot 3 (next larger)	6.3
Shot 4 (largest)	6.3

Part D

Remove the projectiles and smooth the target surface with the ruler. Divide the target into three sections. Find the mass of each projectile and enter the values in the table below. Produce three craters by dropping 3 identical size, but different mass, projectiles from a height of 2 meters above the target surface. Measure the crater diameter produced by each impact. Enter the projectile mass and resultant crater diameters in the table below. Calculate the kinetic energy of each projectile and enter the values in the table below.

	Velocity (m/sec)	Mass (kg)	KE (Nm = kg m2/sec2)	Crater Diameter (cm)
Shot 1 (steel)	6.3
Shot 2 (glass)	6.3
Shot 3 (wood)	6.3

5. Examine the results of parts B, C, and D. Use the completed tables to answer the following questions.
a. How does kinetic energy of the projectile relate to crater diameter?
b. How does velocity relate to crater size?
c. How does mass relate to crater size?
d. How does the size of the projectile relate to crater size?
e. Which is the most important factor controlling the crater size; the size, mass, or velocity of the projectile?

*Part E

Remove all projectiles from the sand tray and smooth the target surface. Divide the sand into two equal halves. In one half form a ridge of sand about 10 cm high and 15 cm wide, and leave the other half smooth. Use intermediate size steel ball bearings and form one crater on the side of the ridge. Form another crater on the flat section, launching it with the slingshot from 70 to 90 cm above the tray. Compare the two craters.

*6. What can you say about crater preservation on rugged terrain versus smooth terrain?