#### by Robin Riordan

**Aims and objectives**

To investigate the way the diameter of a projectile affects the final form of an impact crater. To compare the results from this activity with real craters observed on the Moon and Mars.

## Apparatus

- 1 large high-sided bowl (preferably ~30cm diameter)
- 2 bags of flour
- 2 pots of dry powder paint (one each of two colours)
- 1 flour sifter
- 1 sieve (optional)
- assorted projectiles (of different diameters)
- 1 measuring balance
- 1 ruler
- 1 compass
- 1 pair of tweezers
- 1 spoon
- Aprons and old newspaper / table covering
- data tables / paper / pens

## Experiment, Observations and Measurement

- Preparation
- Put on your apron and roll up your sleeves – this could get messy. Put down some old newspaper or a table covering to catch any “overspill” from the bowl.
- Put an even layer of flour in the high-sided bowl to a depth of approximately 5-6cm. Cover with a thin layer of dry coloured powder paint (any colour will do as long as it contrasts well with the flour underneath. A flour sifter often helps at this point to get an even layering).
- Measure the mass and diameter of each impactor, and record this on your data chart. Use a compass to measure the diameter of spherical projectiles.

- The Experiment Part I: Straight Drop. This is a 90 degree drop.
- Take projectile #1 and drop it onto the prepared surface from a height of 30cm.
- Make a note of the diameter and depth of the crater, and of the number of rays and their length. To measure the diameter, a compass may once again be useful. To measure the depth of the crater, the projectile will have to be removed very carefully with tweezers beforehand. Alternatively, you can measure the depth to the top of the projectile, and add on its diameter to that value. The rays will be visible as white streaks radiating from the crater. Measure each and take an average value. Record all information in your data table.
- Record any other observations you make about the crater.
- Repeat the above with projectile #1, this time dropping it from 60cm, and 90cm. Remember to record all information in your data tables.
- Now repeat all of the above steps for projectiles #2 and #3. Use the data tables provided to record information, or create your own.

**Part II: Angles**

In this part of the experiment you will use the same three masses, whose masses and sizes you have already measured. But, instead of dropping the masses straight down you will be launching them from from two different angles, 60 degrees (a pretty steep angle) and 30 degrees (a pretty shallow angle). Try to make the height of the launch about 1 meter.

Record the same data as you did in Part I.

Projectile | Mass (g) | Diameter (cm) |

1 | ||

2 | ||

3 |

Projectile | Angle(degrees) | Height(cm) | Crater Depth(mm) | Radius of Streaks(cm) |

1 | 90 | 30 | ||

2 | 90 | 60 | ||

3 | 90 | 90 | ||

1 | 60 | 90 | ||

2 | 60 | 90 | ||

3 | 60 | 90 | ||

1 | 30 | 90 | ||

2 | 30 | 90 | ||

3 | 30 | 90 |

## Data Analysis

- Plot graphs using the data you recorded in your tables. Plot Graph 1 as the average crater diameter vs. projectile height and Graph 2 as average ray length vs. projectile height. Plot a line for each projectile on the same graph, using different symbols to identify each projectile.
- Explain what each graph tells you about the relationship between the projectile and the crater.
- If the projectile was dropped from a height of 6m, estimate the size of the final crater from your experimental data.
- Describe and discuss where possible errors could occur in your experiment. In particular, how could your experimental setup and procedure differ from those of another group carrying out the same experiment with the same instructions?
- From your experimental observations, describe the appearance of an impact crater. Give reasons why your craters differ from the real craters observed on the Moon and Mars.