Impact Crater experiments
Dick van der Wateren
When you have done the experiments below, you will be able to answer some of these questions, and maybe some more of your own. Remember: you are completely free to do the experiments as you like and set up new ones!
In these experiments we will find out what kind of craters are produced by meteorite impacts. We will start with a very simple experiment, just observing what happens when a projectile hits a surface. We will then vary, one by one, quantities that may influence the size and shape of your craters, for instance the size of the object hitting the surface, its speed, the composition of the surface.
The last experiments will allow you to predict the size, velocity and impact energy of the meteorites that produced the big craters on the Earth, the Moon etc.
You are completely free to expand these experiments, think of new research questions and to set up new projects.
making impact craters
Experiments are done to test ideas or theories. Before each experiment, think carefully about what you are going to investigate, why you want to do it and what you believe will be the result.
To help you do this, like any other scientist, you will think about the problem, or the research question you wish to answer. For instance:
- Problem: “I want to find out the shape of an impact crater.” (Experiment 1.1)
Or:
- Problem: “I want to find out if big projectiles make bigger craters.” (Experiment 1.2)
Next comes the hypothesis (or assumption), in which you state what you expect will be the result of your experiment. For instance:
- Hypothesis: “I expect that an impact crater has the shape of a circular hole.” (Exp. 1.1)
Or:
- Hypothesis: “A big projectile makes a bigger hole than a small one.” (Exp. 1.2)
Write down your problem and hypothesis before you start your experiment, so you can check it later with your results.
Like with any scientific experiment it is important that you make careful notes of what you do and observe. Record your measurements in tables and plot them in graphs. Make sketches, photos and (if possible) videos of your experiments.
Scientific experiments like these must be reproducible. That means you must perform them and describe them in such a way that others may repeat the experiment and get the same results.
1. simple experiment: crater shapes
Materials:
1. A shallow box or other container. A plastic or cardboard container, the size of A4 paper or larger is fine.
2. Surface material. This can be wheat flour, fine sand or equivalent dry granular medium. (You will later experiment with wet and more or less fluid materials, such as wet sand, wet plaster of Paris.)
3. Coloured medium to coat the surface. This can be cocoa powder, powdered paint, or table salt tinted with food colour. This makes it easier to identify and measure the impact craters.
4. Objects to use as projectiles. You can use a variety of objects, balls of different sizes of wood, styrofoam, steel, rocks, marbles.You may also experiment also with softer objects like blobs of clay or wet sand, water drops (Exp. 1.7).
5. Optional: grab, pair of tweezers, or a magnet on a string, which you need to retrieve your projectile without disturbing the surface medium.
6. Optional: newspaper or plastic sheet to keep the floor clean.
Experiment 1:
Fill the container with the surface medium (flour, sand etc.), using a sieve to distribute it evenly (not with wet sand or plaster of Paris, of course).
Sprinkle the surface lightly with the coloured medium (e.g. cocoa powder) with the use of a fine sieve.
| Before you start, don’t forget to write down the problem (research question) you are going to explore, as well as your hypothesis (assumption). |
Drop the projectile from different heights: knee-high, shoulder-high and as high as you can reach. Try to drop it on an undisturbed part of surface.
Carefully study the shapes of your first impact craters. Make sketches/photos.
Do all have the same shapes? If not, can you think of a reason?
Note also the material that has been thrown out of the crater, the ejecta. Count the number of ejecta rays and measure their lengths.
Do you find any relation between drop height and number or length of the rays?
Can you explain it?
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. Do they agree with what you expected? Do not be afraid that you made a mistake if they do not. This is how science progresses.
You have learned something new!
Now for the next experiment
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 |
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?
3. varying projectile mass
The problem of this experiment will be something like “I want to find out if heavier projectiles make bigger craters.”
By now, you will probably have got the hang of it. In this experiment, just vary the mass of the projectiles (steel, glass, wood, foam etc.), not their diameters or the height from which you drop them.
Materials:
1-7
8. Small scale. An electronic scale or balance is ideal to determine the mass of the projectiles.Make a table noting the projectile masses and crater diameters and construct a new graph.Make an other table noting the projectile masses and ejecta ray lengths and construct a graph.
4. varying impact velocity
The problem of this experiment will be something like “I want to find out if high velocity impacts produce bigger craters than low velocity ones.”
Again, think carefully before you set up your experiment. For instance, will doubling the impact velocity produce a two times bigger crater? What is big: diameter, area, or volume of the crater? Then think of a clever hypothesis.
Materials:
1-8
9. 2-metre graduated ruler, tape measure, or other height-measuring device (can be longer if you wish). You will need this to measure the height from which you drop the projectiles. You can build something similar to the diagram from bits of wood lying around. The platform is important since it ensures that you launch your projectile with zero starting speed every time. See illustration.
Repeat the experiment three times for different drop heights, doubled each time, e.g. 25, 50, 100 and 200 cm. Use the same projectile throughout. Measure diameters and depths of the craters as well as number and length of ejecta rays and be alert for changes in shape.
Record your observations in a table as usual and construct graphs (crater diameter and depth against drop height).
Does doubling your drop height also double the impact speed? Is there a way to measure the speed, or calculate it from the drop height?
5. varying impact angle
Use a one-metre long pvc tube or similar device to launch your projectile at different angles. Do not hold its lower end more than 5 cm above the surface.
Carefully measure the angle each time. Observe changes in crater shapes and number and length of ejecta rays. Think of a way to quantify the varying crater shapes (e.g. ratio between smallest and greatest diameter). Record your observations in a table and a graph.
6. varying surface medium
It’s now time to see what happens when you use some material other than flour to drop your model meteorite on. It is important that you find a way to compare the different results in a quantitative way (i.e. with numbers). Think about it and discuss it with your classmates.
A good way may be repeating some of the previous experiments with different surface materials. Compare the graphs.
Experiment with dry and wet sand. If you use wet plaster of Paris (sprinkled with powdered paint) you may let is harden. You can then hang your own meteorite crater on the wall of your room at home.
7. varying projectile composition
So far, you dropped projectiles that were harder than the surface. What happens when they are softer and disintegrate upon impact? Experiment with materials of a colour different from that of the surface material. You will then see how and how far the fragments of the projectile are scattered during impact.
You may use blobs of clay, wet plaster of Paris, wet sand, or even water drops. Find the best combination of projectile and surface materials.
Do you see any changes in the shape of the impact craters? Make photos and compare them with photos from craters on the Moon, Mars and other planets.
8. calculating velocity, acceleration, energy, force
If you are already familiar with mechanical equations you may have a go at calculating velocities and kinetic energies during impact. You will see that your graphs will be more useful than when you only recorded drop height.
The following equations will be helpful:
Impact Velocity: vf = vo + a·t, or: vf2 - vo2 = 2·a·d
where vf and vo are final and original velocity, respectively, a is acceleration, t is time and d is distance travelled.
Kinetic Energy: Ek = 1/2 m·v2,
where m is mass and v is velocity.
Now you can make predictions about meteorite and asteroid impact velocities for real craters, by extrapolating your plots to larger diameters and shapes. Start with predictions that you can check with an experiment, e.g. predict a drop height for twice the diameter of your largest crater. First extrapolate your plot to the new crater dimensions and read the predicted drop height from your graph. Experiment until you have found the correct drop height and check if your prediction was correct. If it was not, what could have been the reason? Use your new insight in the next experiment.
Make a prediction for ‘real-life’ impacts. From a database of craters on Earth select a few examples of small and large craters. Estimate the impact energies and velocities for these craters. Find out on the Internet if your predictions are at least halfway realistic. Can you improve your predictions?
9. Why do some parts of the moon and planets have more craters than others?
Only 171 impact craters have been recognized on Earth. Outside the Earth they are not so rare. If you look at the Moon, even with your naked eyes, you can see large circular spots marking its surface. Some of them may be volcanoes, like the majority of circular features on Earth. But most of them are impact craters.
Use a telescope, or a pair of binoculars, or find a map of the Moon. You will see many of these circular spots, some very large, some overlapping. The Moon’s surface is absolutely littered with them. It seems the Moon was bombarded by millions and millions of small and large objects.
Look at the beautiful maps of Mars that were made during the US and European missions to our neighbour planet (see links to ESA and NASA ). There are few places that are not covered with impact craters.
You will remember that all of the planets and their moons have been constantly bombarded since the beginning of the Solar System, billions of years ago. Now, if some surfaces show less scars than others, something must be different.
At this website you will learn about these differences and how you can find out the age of a surface by just counting the number of craters.
10. The dangers of Near Earth Objects – Guard the Earth
The Near Earth Objects Fact Sheet (link ) shows that there are thousands of objects that could threaten our existence on Earth.
Here you can take part in a project to identify and track the most dangerous Near Earth Objects (link ). See also this map of the Solar System with all known NEO’s.
You don’t need expensive equipment to become an Earth Guardian. You can see the bigger and most dangerous ones even with a small telescope. Maybe your school owns one, or you can go to an amateur observatory in your town.
verry nice we must make a movie from the impact Write Comment | |
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