(This is the eleventh Astronomy 210L laboratory at Cuesta College, San Luis Obispo, CA. This course is a one-semester, optional adjunct laboratory to the Astronomy 210 introductory astronomy lecture, taken primarily by students to satisfy their general education science transfer requirement.)
Let's first consider impact events from the distant, and also not-so-distant past.
Notably the "K-T" (Cretaceous-Tertiary) extinction event about 65 million years ago.
What would happen if you were a dinosaur living at that time? According to this artistic depiction, the ceratopsid on the left may have already perished from the blast wave, or maybe has just laid down due to the sheer despair of acknowledging its impending doom. Or maybe you would feel more like the plesiosaur on the right, either surfing its last killer wave, or asphyxiating from lack of oxygen.
Consider a much smaller event about a century ago in remote Siberia.
The air blast from this event devastated the landscape below, fortunately far away from inhabited areas.
So why wait around for the next impact event to happen on Earth?
Which is what you get to do in laboratory today.
By dropping objects of different mass, or different height, you can create different energy impact events.
By plotting the different impact energies versus impact crater diameters, you can determine the cohesion of a material, and the type of cratering process in this material.
Plotting different impact energies versus crater diameters should result in a linear data set, as graphed with "log-log" scales.
And by drawing a best fit line (not just "connecting the dots") for your data set...
You can slide a slope template to find the impact cratering process that best fits your data set.
EQUIPMENT
15 cm rulers (small, flexible)
meter sticks
material containers
medium-grain playground sand
coarse water softener salt
fine-grain table salt
baking soda
stainless steel balls
digital weight scales
hanging mass set (10 g, 20 g, 50 g, 100 g, 200 g, 500 g, 1000 g)
"Impact Energy vs. Crater Diameter Log-Log Graph"
"Impact Process Template"
BIG IDEA
Depending on the specific circumstances, an impactor will create a crater in a target material principally due to one of four processes:
- Avalanche (splash): crater diameter set by how much material falls in around impactor.
- Surface crack/pulverization (thud): crater diameter set by surface disturbed by impactor.
- Compression (crunch): crater diameter set by material crushed beneath impactor.
- Excavation (spray): crater diameter set by material thrown outwards by impactor.
Students will conduct a series of inquiries about impact processes by varying different impactor and target parameters, and be able to quantitatively categorize different types of impact processes.
TASKS
(Record your lab partners' names on your worksheet.)
1. Exploration
- Carefully observe a stainless steel ball falling from 50 cm onto medium-grained sand, as measured from the top of the sand surface. Try this several times; note that you will need to cover your sand box and shake it vertically up-and-down a set number of times between each drop to consistently "reset" your sample surface between each drop.
Discuss in your group the hypothesized process(es) of crater formation (i.e., "splash, thud, crunch, or spray," and briefly explain what you observed to support your choice(s). Do not worry about guessing the "correct" answer, this is just a preliminary hypothesis. You may note dissenting opinions, if any.
Medium-grain sand crater process hypothesis: __________.
Explanation of choice: __________.
- How the diameter of an impact crater is measured is a qualitative decision. Thus it is important to measure these diameters consistently. In order to do this, first make several trial impacts from different heights (do not record data yet), and discuss and agree in your group on a consistent description of a crater edge that can apply generally for impactors dropped from heights ranging from 10 cm to 100 cm, as measured from the top of the surface. Also record the mass of your stainless steel ball, in grams.
Description/drawing of crater "edge" definition: __________.
Mass of stainless steel ball: __________ g.
- Release (do not throw down) the impactor from 10 cm to 100 cm, in 10 cm increments, as measured from the top of the surface of medium-grain sand (in order to vary its energy), and measure its crater diameter. Make at least three drops for each height in order to test for consistent results. Then for each drop height, calculate the impact energy (in kiloergs) = (mass, in g)*(height, in cm), and the average crater diameter. (Example: a 50 g impactor released from 20 cm would have 50*20 = 1,000 kiloergs of impact energy.)
Make a table compiling your drop heights (in cm), impact energies (in kiloergs), and crater diameters (in cm).
Impactor
height (cm):Impact
energy (kiloergs):
Crater diameters (cm):Average crater
diameter (cm):10 cm _____, _____, _____. 20 cm _____, _____, _____. 30 cm _____, _____, _____. 40 cm _____, _____, _____. 50 cm _____, _____, _____. 60 cm _____, _____, _____. 70 cm _____, _____, _____. 80 cm _____, _____, _____. 90 cm _____, _____, _____. 100 cm _____, _____, _____. - Plot the data points from (c) on a group "Crater Diameter vs. Impact Energy Log-Log Graph," and use a ruler to draw a straight best-fit line across the entire graph.
The slope of your "Impact Energy vs. Crater Diameter Log-Log Graph" is related to the specific cratering process involved. Place the "Impact Process Template" over your graph, and slide it left or right while keeping the horizontal and vertical baselines aligned to determine which impact process slope is most parallel to your best-fit line.
Does your data support or refute your original cratering process hypothesis? Explain your reasoning and provide specific evidence from data to support your reasoning.
3. What Conclusions Can You Draw From This Evidence?
The table below summarizes the results of dropping different mass impactors, all from the same height (20 cm) into medium-grain sand.
| Impactor
mass (g): | Impact
energy (kiloergs): |
Crater diameters (cm): | Average crater
diameter (cm): |
| 10 g |
| 3.0, 3.0, 2.8, 3.0, 2.5 cm |
|
| 20 g |
| 3.0, 3.8, 3.3, 3.5, 3.5 cm |
|
| 50 g |
| 3.5, 4.2, 4.9, 5.0, 5.1 cm |
|
| 100 g |
| 5.0, 5.2, 5.5, 5.0, 5.4 cm |
|
| 250 g |
| 6.0, 7.0, 6.2, 5.8, 5.9 cm |
|
| 500 g |
| 7.0, 8.8, 8.2, 7.5, 8.0 cm |
|
What conclusions and generalizations can you make from the information given above in terms of "Does varying impactor energy by varying mass (while keeping drop height constant), and by varying drop height (while keeping mass constant) give the same results for determining medium-grain sand cratering processes?" Explain your reasoning and provide specific evidence (a group "Crater Diameter vs. Impact Energy Log-Log Graph," with data points plotted, and best-fit line), to support your reasoning.
4. What Evidence Do You Need to Pursue?
Recall that you covered your sand box and shook it vertically up-and-down between each drop to consistently "reset" your sample. Consider the following claim:
"If the sand box is shaken side-to-side between each drop, the sand grains will sift and settle, becoming more tightly compacted for the next drop from the same height."Describe precisely what evidence you would need to collect in order to answer the research question of, "How does a 'side-to-side reset' for medium-grain sand affect the results of each subsequent drop from the same height?" You do not need to actually complete the steps in the procedure you are writing.
Create a detailed, step-by-step description of evidence that needs to be collected and a complete explanation of how this could be done--not just "drop the ball multiple times," but exactly what would someone need to do, step-by-step, to accomplish this. You might include a (blank) table and sketches--the goal is to be precise and detailed enough that someone else could follow your procedure.
5. Formulate a Question, Pursue Evidence, and Justify Your Conclusion
Design an answerable research question), propose a plan to pursue evidence, collect data, and create an evidence-based conclusion about an aspect that you have not completed before. (Have your instructor approve your whiteboard research question before proceeding further.)
Research report summary on whiteboards/poster paper, to be worked on and presented to the class as a group, should include:
- Specific research question.
- Step-by-step procedure to collect evidence.
- Data table and/or results (including graph(s)).
- Evidence-based conclusion statement.
Procedure adapted from Gary Parker, "Low Velocity Impact Craters In The Lab," presented at Cosmos In The Classroom 2004 (*.html).
No comments:
Post a Comment