Impact Craters on the Moon
Craters form when an object strikes the surface of a planet, moon, or other object in outer space. Craters are also found here on Earth as well. The energy from the impact of an object such as a meteorite or asteroid is transferred to the surface that it strikes. The energy from the impact forces the surface it strikes to move. Material from the surface is thrown from the impact area to form a ring of material calledejecta. The crater can contain rocks that were changed from the impact, which are oftenbroken or melted. Craters arecircular, andabout 10 times larger than the diameter of the object that formedit.
The size, mass, speed, and angle of the falling object determine the size, shape, and complexity of the resulting crater. Small, slow-moving objects have low impact energy and cause smallcraters. Large, fast-moving objects release a lot of energy and form large, complex craters. Very large impacts can even cause secondary craters, as ejected material falls back to the ground, forming new, smaller craters, or a series of craters.
Craters can be classified into 3 basic types:
Simple impact cratershave bowl-shaped depressions, mostly with smooth walls. This type of crater generally has a diameter less than 9 miles (15 km). Their depth is about 20% of their diameter.
Complex impact cratershave one or more peaks in the middle of the crater. These craters have diameters between about 12 and 110 miles (20 and 175 km), and the central uplift is usually one or a few peaks. Craters with a diameter over 110 miles (175 km) can have more complex, ring-shaped uplifts within the crater.
AnImpact Basinis an impact crater that has a rim diameter greater than 185 miles (300 km). There are over 40 impact basins on the Moon. These catastrophic impacts cause faulting and other crust deformations. Material ejected from impact basins is distributed over wide areas.
The total mechanical energy of an object is the sum of its kinetic energy (KE) and potential energy (PE). A meteor, asteroid, or some other object in deep interplanetary space loses potential energy and gains kinetic energy as it falls toward and impacts the surface of the celestial body.Since initial PE equals final KE at the point where the space object collides with a celestial body’s surface, the impact velocity of object can be calculated using the math formula:
Where “h” represents height and the gravitational constant, “g” is the acceleration of the object due to gravity. This acceleration is about 9.8 meters per second on Earth.
Problem:
Simulate impact crater formation.
- Metric ruler
- Forceps
- Newspaper
- Small shallow pan or box
- White baking flour
- 1 medium-sized rock
- Images of craters on the Moon and other planets
- Calculator (optional)
- Prepare for the investigation by placing the newspaper on the floor.
- Fill the pan with flour to a depth of 5 cm.
- Shake the pan gently to smooth the surface and then place it on the newspaper.
- Using the metric ruler, drop the rock sample from a height of 25 cm above the surface of the flour.
- Use the forceps to remove the rock.
- Measure and record the depth of the crater and diameter of the crater
- Measure the distance between the crater and wheremost of the flourwas ejected (ejecta) when the rock hit.
- Repeat steps 4 through 7, dropping the same rock from a height of 50 cm, 75 cm, and 100 cm (one meter) above the surface of the flour in different parts of the pan. (The higher the drop height, the faster the rock will hitthe flour surface.)
- Record the depth of each crater in a table similar to the one below..
- Make three trials for each height and compute the average values.
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Drop Height
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Crater Impact Measurement Data
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|||||
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25 cm
|
DepthofCrater Diameter of Crater Ejecta Distance |
Trail 1
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Trail 2
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Trail3
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Total
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Average
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50 cm |
Depth of Crater DiameterofCrater Ejecta Distance |
Trail 1
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Trail 2
|
Trail 3
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Total
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Average
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75 cm |
Depth of Crater Diameter of Crater Ejecta Distance |
Trail 1
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Trail 2
|
Trail 3
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Total
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Average
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100 cm
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Depth of Crater Diameter of Crater Ejecta Distance |
Trail 1
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Trail 2
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Trail 3
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Total
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Average
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- Calculate the rock’s impact velocity when it strikes the surface of flour by using the formula.
|
Drop Height |
Height in Meters
|
Acceleration due to Gravity |
Impact velocity (m/s) |
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25 cm
|
980 m/s2
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50 cm
|
980 m/s2
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||
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75 cm
|
980 m/s2
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||
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100 cm |
980 m/s2
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- Using graph paper or a computer equipped with Excel® use the data written in the two tables and plot a series of line or bar graphs of the following:
Average Crater Diameter vs. Rock Velocity
Average Crater depth vs. Rock Velocity
Average Ejecta Length vs. Rock Velocity
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