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Page 4 of 10
 2. varying projectile size
The problem of this experiment will be something like “I want to find out if bigger projectiles make bigger craters.”
Think carefully about this problem. What do you mean by big? Is it size, mass? Will a large styrofoam ball make the same impact as a small steel ball? You see that it is very important to describe exactly what you do. Then think up a hypothesis.
Materials:
1-6
7. Ruler + 2 blocks, a calliper, pair of dividers, or other size-measuring apparatus, to measure the diameter of the projectiles.
Experiment 2:
It is important that you change one thing at the time. If you don’t, you will not be able to come to a good conclusion. For instance, if you drop a small steel ball from one metre in your first try and a big foam ball from two metres in the next you will never know if it was size or mass that made the difference. So, use the same material and height, and only vary the size of the projectile.
Make a table in which you note the diameters of both the projectiles and the craters. Don’t forget to note the height from which you dropped the projectiles.
| Projectile material: ...................... |
Drop height: ............cm |
| projectile diameter (mm) |
average crater diameter (mm) |
average ejecta ray length (mm) |
other observations |
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Measure the diameter of each crater. Since they will not be perfect circles you need to measure several diameters and calculate the average. Note that in your table. Make a graph of crater diameter against projectile diameter.
Measure the length of the ejecta rays. Again calculate average lengths for each crater. Make a graph of ejecta ray length against projectile diameter.
After a few experiments, you will need to level the surface again and sprinkle a fresh layer of coloured medium on it.
Conclusions:
Write down your conclusions. What did you learn?
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