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IMPACT CRATERING
Purpose of the laboratory exercise:
Students learn to take their own data, record it, analyze it, and create a scientific
hypothesis from it. These hypotheses will enable the students to make a prediction.
Students also learn to work with the metric system.
Objectives:
- To form impact craters in a classroom environment
- To understand the formation process and structure of impact craters on the Earth
and terrestrial planets.
- To learn the effects impact cratering has had and will have on the Earth and the
planets.
Materials:
- Large tray (aluminum Turkey Roasting pan works well) 70cm x 70cm (2'x2' at least)
between 10-15cm deep
- Sand to fill tray to ~3" deep, fine sand is best
- Three balls of the same size, about 1", of differing weight (e.g. a ballbearing,
a wooden ball, and a styrofoam ball)
- Three marbles of different size
- 2 dark colors of dry tempera paint, e.g. purple and green, or colored sand and salt-
you will need 2 colors besides the plain sand
- ruler (in cm preferably)
- Safety goggles, if desired
- scale to weigh projectiles, or known weight of projectiles
- meter stick, if desired
- Plant sprayer (optional part)
- Plastic shovels or cups (for scooping sand)
Motivation:
Since the formation of the solar system, meteorites have been forming impact craters
on the surface of all the solid planets and their moons. This process has been important
in the evolution of the planets. Cratering caused early melting on the planets and excavated fresh sub-surface material. One motivation for these lessons is to learn
about mass extinction, one effect impacts have had on life on Earth. The planets
that do have hard surfaces, like Earth, are called terrestrial planets. The surfaces
of these planets are covered, in some cases almost entirely, by impact craters. The
nearest example of a heavily cratered surface is the Earth's own moon. It has preserved
many of the craters formed by the meteorites that have impacted it since its formation. The last stage of planetary formation, about 3.9 billion years ago, is when
the moon acquired most of its craters. At this time in the history of the solar
system, there was an abundance of rock, ice, gas and debris pieces floating in space,
crashing into any terrestrial surface in the area. The craters formed on Earth at that time
have long since been destroyed by geologic processes such as weather, erosion and
continental drift; many of these processes are unique to the Earth and her atmosphere.
After 3.9 billion years, the number of meteorites loose in our part of space decreased
to what it is today.
Part 1: Formation of Impact Craters
In this part of the lab exercise, we will be forming impact craters. You will need
to be able to do these things:
- Take measurements in the metric system (not inches)
- Work together in a group
- Follow instructions carefully
Pre-question: Ask the class what factors they think will effect the size of the craters
they are going to make.
How Mass Affects Impact Craters
Class should make a prediction on what they think the effect of mass will be on the
craters - what will a small mass make versus a large mass.
Procedure:
Note:
If a scale is not available and the mass is unknown, just use numbers to rank the
masses, e.g. 1,2,3 for the light, medium, and heaviest masses.
Step 1: Fill the tray with sand, about 1/3 full.
Step 2: Smooth the sand out with the meter stick or ruler, sprinkle a thin layer of
salt on top, enough to cover the sand.
Step 3: Fill in the mass of each object in the table below, ask your teacher the
mass of each object or weigh it yourself if scales are available.
Step 4: Drop your first ball into the tray, measure the distance across the crater,
which is called the diameter, and record it in the chart.
Step 5: Smooth the sand out with the meter stick or ruler, sprinkle a thin layer of
salt on top, enough to cover the sand.
Step 6: Drop the second ball into the sand, measure the diameter of the crater, and
record it in the chart.
Step 7: Smooth the sand out with the meter stick or ruler, sprinkle a thin layer of
salt on top, enough to cover the sand.
Step 8: Drop the third ball into the last area, measure the diameter of the crater,
and record it in the chart.
OBJECT OBJECT TYPE OBJECT MASS CRATER DIAMETER
BALL #1 g cm
BALL #2 g cm
BALL #3 g cm
QUESTIONS
1. Compare your 3 craters- which crater is the largest? Which ball created it?
2. What's the only difference in the way you made the craters?
3. Finish this statement: The ____________the mass, the _____________the crater.
(bigger/smaller) (bigger/smaller)
ADVANCED ACTIVITY
For more advanced grades, have the students plot the data for each section. For this
section, the graph of the trials should be a straight line ( plot mass vs. crater
size -- x vs. y). Then you can draw the line as far out as you want to obtain an
estimate of crater size for really large objects. Try for 1 metric ton, 2,000 kg!
How Speed of Meteorites Affects Impact Craters
Class should make predictions on how a greater or smaller speed will effect the size
of the crater.
Note:
Explain to the class that the farther a marble falls, the greater its speed (within classroom limits).
Step 1: Take out the big marble.
Step 2: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 3: Drop the marble from a height of 10cm, record the crater diameter on the chart
Step 4: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 5: Drop the marble from a height of 1 meter, record the crater diameter on the
chart
Step 6: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 7: Drop the marble from a height of 2 meters, record the crater diameter on the
chart
Step 8: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 9: Ask your teacher to throw the marble into the sand, or ask you teacher for
permission to throw it. Record the crater diameter.
Drop # velocity height crater diameter
1 140 cm/s 10 cm cm
2 443 cm/s 100 cm cm
3 626 cm/s 200 cm cm
4 1000 cm/s 200 cm cm
QUESTIONS
1. Compare your craters. Which is the largest?
2. What in the only difference in the way you made the craters?
3. Finish this statement: The __________ the velocity, the ___________ the crater.
(bigger/smaller) (bigger/smaller)
ADVANCED ACTIVITY
For this graph, the relationship is not a straight line, instead try to fit a curve
to the points, do not juse connect them. The curve should be half a parabola if
the data is accurate.
How Size of Projectiles Affects Impact Craters
Class should make a prediction on how a greater or smaller size projectile will effect
the size of the crater.
Step 1: Take out the 3 different size marbles
Step 2: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 3: Drop the smallest marble from a height of 2 meters
Step 4: Without disturbing the sand, measure the crater's diameter
Step 5: Record the diameter in the chart below
Step 6: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 7: Drop the middle size marble from a height of 2 meters
Step 8: Without disturbing the sand, measure the crater's diameter
Step 9: Record the diameter in the chart below
Step 10: Smooth out the sand with the ruler, sprinkle a thin layer of salt on top,
enough to cover the sand.
Step 11: Drop the biggest marble from a height of 2 meters
Step 12: Without disturbing the sand, measure the crater's diameter
Step 13: Record the diameter in the chart below
Object marble diameter crater diameter
small marble cm cm
middle marble cm cm
big marble cm cm
QUESTIONS
1. Compare your craters. Which is the largest?
2. What in the only difference in the way you made the craters?
3. Finish this statement: The __________ the marble, the ___________ the crater.
(bigger/smaller) (bigger/smaller)
ADVANCED ACTIVITY
For the graph of this section, the relationship should be linear, although with such
small, slow moving projectiles, the data can be inaccurate. Nevertheless, try to
fit a straight line to your data and extend the line (you may want to change the
scale of the graph) to look at a 15 km diameter meteorite. This is about the size of the
meteorite that is believed to have killed the dinosaurs.
OPTIONAL --Advanced Exercise Kinetic and Potential Energy
In this activity there are two types of energy involved in the marble's fall, kinetic
and potential. Let's look at potential and kinetic energy and then study their relationship.
When you hold the marble above the sand, it has a mass and gravity is pulling down
on it. Believe it or not this marble has energy you hold it there. the energy is
called potential energy; it is the energy representing the force of the Earth's gravitational pull.
In this case, the ball is being held up by the table, thus its potential energy is equal to its:
mass x the height of the table x gravity.
The formula for calculating potential energy is (mass)x(gravity)x(height), or m g h,
where gravity = 980 cm/s/s, the height is in cm, and the mass is in grams.
Calculate
the potential energy for the marbles in the velocity experiment.
Marble 1:
Marble 2:
Marble 3:
Marble 4:
When you released the marbles they no longer had the same potential energy, in fact
as they fell, their potential energy became kinetic energy. Kinetic energy is the
energy of bodies in motion. The formula for calculating kinetic energy is (1/2)x(mass)x(velocity)x(velocity) or 1/2 m v v or 1/2 m v2.
Calculate the KE for each marble.
Marble 1:
Marble 2:
Marble 3:
Marble 4:
Since the only energy involved here (for our purposes) is Kinetic and Potential, then
the energy we just calculated should be equal. Why is it not equal for marble 4?
What was different about the way Marble 4 was "launched"?
answer: Marble 4 was given extra acceleration when you threw it into the sand, therefore
it had extra speed so the kinetic energy came partly from potential energy and partly
from your kinetic energy! The other marbles had only kinetic energy from their potential energy.
Part 2: Crater Structure
We have just seen that 3 factors effecting the size of a crater are mass, speed and
size of impacting meteorite. One of the best ways to examine a crater's structure
is to make a fresh young crater. In this continuation of the Impact Cratering Lab,
we will look at the parts of a fresh, young crater.
In this part of the lab exercise we will again be forming impact craters. You will
need to need to be able to do these things:
- Sketch at least one view of your crater
- Make observations and hypotheses about the crater parts
- Follow instructions and work in groups
A. Procedure and Questions
Pre-question: Ask the class what they think the crater will look like since they have
just formed a lot of them in their trays.
Parts of an Impact Crater
Note: it's important that layers completely cover each other
Step 1: Smooth out your first layer of sand and coat it with a generous layer of
salt. It should be a little thicker thatn the thin layers you've used before.
Step 2: Sprinkle a layer of tempera paint over the salt
Step 3: Take the large marble and drop or throw it from a height of ~2m
Step 4: Observe the crater: make a drawing from overhead labeling (guess) the rim,
ejecta and crater floor.
Step 5: Measure the crater diameter. How does it compare with the diameter from
the last big marble drop?
QUESTIONS
1. Where is the ejecta thickest?
right along the rim
2. If the sand layers from top to bottom are youngest to oldest, where in the new
crater do you find the oldest rocks (beside the floor)?
in the surrounding ejecta blanket
+ Return to Lesson Plan List
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