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== Age ==
{| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
| [[Astronomy]]:
| Crater Formation
|-
| Grade Range:
| [[Elementary School]], [[High School]]
|-
| Format:
| [[Hands-on]]
|}


Elementary School,Middle School,High School
The Crater Box is a simple way to show how craters form. This is an easy hands-on experiment that younger students will enjoy, if only because they get to throw balls in a sand box. This demonstration fits well into a high-school astronomy course, since you can demonstrate how to calculate the size of an object based on the dimensions of the crater it leaves behind.


== Format ==
== Materials ==


Hands-on
* A Large, Flat Box
* A Mix of Coarse and Fine Sand
* Small Balls of Varying Size and Mass
* Yard Stick
* Ruler (optional)


== Materials ==
    Sandbox
    Sand of varying grain size
    Steel balls of varying sizes


== Safety Precautions ==
== Safety Precautions ==


Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Safety glasses to prevent sand being kicked into eyes. Don’t let the kids throw the balls into the sand, only drop!
Please read the Physical Demonstration section of the [[Demonstration Safety]] page before performing this demonstration.


== Preparation ==


Sand needs to be filled in boxes that have high enough walls to keep in most sand and from being kicked out into eyes
== Demonstration ==


== Demonstration ==
# Ask a student to drop one of the balls into the box, from about one foot above the sand. Let them drop a few different types of balls, so they can see how the mass of the ball affects the outcome.
# Ask the student to now drop a ball from two feet up. Can they see a difference in the depth of the crater? What about the width?
# Ask the student to now drop a ball from three feet up. Ask again if they can see a change in the width or depth of the crater.
# Optional: If students would like, they can use the ruler to measure the width and depth of the hole at the different heights. Do they see a trend forming?


Drop varying sizes of balls into sandboxes with grains of varying sizes. Demonstrate that impacts form craters because the material is pushed aside by the projectile, often times throwing material upwards/outwards. Show that as the height increases, the diameter and depth don’t increase nearly as much as the height. Explain that this is due to the sand acting as a solid at the moment of impact.


For the latter part of the demonstration, repeat the experiment in a vacuum to demonstrate that the lack of air causes a the craters to look different. (Further research is needed to explain why).
== Why This Works ==


== What to Say ==
===Short Explanation===
Crater formation is easy to see and understand. An object comes in from outer space, strikes a planet or moon, and that impact results in a hole on the surface. We can replicate this using this box of sand and set of balls, and look at what you need to make bigger craters.


Start by discussing the craters of the moon and asking if they know where they originate. Introduce the concept of meteor impacts in the early solar system and how the moon and planets would have been bombarded by meteors early in their history. If asked why there were many meteors explain that when the solar system was formed there was lots of debris left over that formed many meteors.
When you drop the different balls in at different heights, you see that the more mass the ball has, the bigger the crater it makes. This is because the amount of energy our ball has depends on two things: how big it is, and how fast it is going when it hits the sand. Since we are dropping the balls instead of throwing them, we can have them all be moving at about the same speed when they hit the sand. This means that the only thing that changes the outcome is how much mass each ball has. In other words, the bigger and heavier the ball, the bigger the hole it will make!


Show the different sized balls and different boxes of sand and explain what they’ll be doing. After the kids drop some of the balls and made craters, explain the concept of transfer of energy and how it relates to the demo. Explain how the craters get larger when the ball is dropped from a greater height and touch on the notion that the sand acts like a solid at the moment of impact which causes the ball to lose energy and how that causes the crater size and depth to be not directly proportional to each other (meaning that if the height is doubled, the crater size/depth is not doubled).
We can see that the craters are all forming in similar ways, whether they are big or small. This is because craters have three stages of formation. The first stage is the '''Contact Stage''', when the ball hits the surface. The second stage is the '''Excavation Stage''', when some of the sand is sent flying by the impact, and we see the hole widen up from the ball's impact. The final stage is the '''Modification Stage''', when we see the walls of the hole collapse a bit, and the flying sand lands again. The craters are not very big, however, and that is because it takes a lot of energy to make the sand move out of the way ''without'' scooping it. In fact, to double how wide the hole is you need to drop the ball eight times higher, and to double how deep it is you would have to drop the ball from sixteen times higher!


Explain that there is no air in space and perform the demonstration in the vacuum tube and note the difference in structure. This would simulate how impacts affect the moon as opposed to the earth.
===Full Explanation===
Crater formation is easy to see and understand. An object comes in from outer space, strikes a planet or moon, and that impact results in a hole on the surface. However, the dimensions of the crater formed, and what factors into the dimensions of it, are a bit harder to comprehend.


A demo might go something like this:
When we drop a ball into the sand, and as we drop it from higher heights, we can see the three stages of crater formation happening. We first see what is called the '''Contact Stage''', when it first strikes the surface. The ball will sink into the surface, compressing some of the sand, and creates a pressure wave in the sand itself. As this pressure wave travels out through the sand, it pushes some of the sand around the ball up and away from the impact. This is the '''Excavation Stage''', when we see the bits of sand being flung up around the ball, and we see the crater's width form. Right after this we see the '''Modification Stage''', when some of the sand forming the crater wall collapses into it, finishing the shape and size of the crater.


    “How many of you have ever looked at pictures of the moon and seen all those craters all over it?”(likely they have)
When we drop the ball from differing heights, we are affecting how much energy it has when it strikes the sand. In this case, we are looking at the relationship between '''Potential Energy''' (''PE = mgh'') and '''Kinetic Energy''' (''KE = 1/2 mv^2''); By increasing the drop height, we are increasing the final velocity of the ball, which affects the final dimensions of the crater. When a crater forms, the initial crater before any collapse will normally be spherical, and will have a depth and width that are proportional to the size of the object. If we measure the width and depth of the craters formed by the balls in the sand, we should start to see a trend that both of these factors are increasing. They both increase slowly, however, with the width of the crater growing faster than the depth of it. This is because of the spherical shape a crater takes on; the volume of a sphere can be calculated with a cubed diameter, and the crater formed will never have a volume greater than 1/3 of an imaginary sphere placed within it. We can combine these terms to find:
    “Well, where do all of those come from?” (likely no one will know)
    “Well, when the solar system was first forming, there was all kinds of left over stuff floating around in space. This stuff was a bunch of meteors, which are really just rocks floating in space. All these meteors were constantly smashing into the planets and the moon. What we’re going to do is make our own craters!” (kids oo-ing and ah-ing)
    “What we have here are sandboxes with different kinds of sand from fairly normal sand to really fine grain sand (point out the boxes to show the difference) and a bunch of balls to drop into the sand to make craters! What I want you to do is to try dropping different sized balls into the sand from different heights and see what happens.” (after kids have dropped several balls proceed)
    “So what’s happening is that when the ball hits the sand it pushes the sand away and a lot of times kicks it into the air. This is because of something called “transfer of energy”. The ball is transferring the energy from its fall into the sand and because the sand is loose, it gets pushes it aside before stopping.”
    “You may have noticed that when you dropped the balls from a really high place, the crater got bigger, but not much bigger. It gets bigger because the ball has lots more energy when it hits the sand when it starts from a higher spot (demonstrate to be sure they see it) but, when the ball hits the sand it’s going so fast that the sand acts sort of like a solid and doesn’t let the ball push it away so some of the energy it got from falling is taken away. Since it doesn’t have as much energy; it doesn’t push as much sand.” (This is quite a lot to say at once, try to include some demonstration in the speaking to break up the monotony and hold attention. It may be opening a can of worms to talk about how it acts like a solid at impact in this demo and would be accompanied well by the Outrageous Ooze demonstration so they can see how this works for themselves)
    The comparison can be made to water where it’s easy to place your hand in the water, but if you jump from a high place it can hurt (belly flops).
    “So this works pretty well here on earth, but on the moon there’s almost no air. So now were going to try this out in a vacuum tube. A vacuum tube is just a tube that we sucked the air out of.” (do the demonstration and show how it looks different than when it’s dropped in air)
    “This is a lot like what the moon is like.”
    “So why don't we see any craters on the earth like we do on the moon? (random explanations) Well, the earth has a lot of geological activity. Geological activity is something like wind blowing things around, water washing things away, earthquakes, tornadoes, rain, snow and any sort of weather that can change the way the land looks. So on the earth, all this activity covers up the craters.” (Demonstrate this by shaking the box)
    “The moon doesn't have this geological activity, so the craters will stay there for a loooonng looonng time.”
    “Any questions?”


== Why It Is ==
{| class="wikitable" style="color:black; background-color:#ddd; text-align: center; margin: auto"
| '''Diameter d<sup>1/3</sup>'''
| '''∝'''
| '''1/2 mv<sup>2</sup>''' = '''mgh'''
|-
| '''Depth d<sup>1/4</sup>'''
| '''∝'''
| '''1/2 mv<sup>2</sup>''' = '''mgh'''
|}


Notice that the proportionality is not a one to one correspondence (doubling the height does not double the crater size or the depth). This is because at the moment of impact, the granular medium “seizes up” and reacts similar to a solid causing energy to be lost.
If we want to see the crater from the two foot drop get twice as wide, we would have to drop it from eight feet high! Also, in order to see the crater get twice as deep, we would have to drop the ball from sixteen feet! If we drop objects from the edge of the atmosphere, however, they will reach a max velocity because of the air slowing it down. In that case, we would instead have to adjust the object's mass is in order to see larger craters. This is why little meteoroids falling to earth don't usually leave a mark, but bigger ones will!


The above equations state, in simpler terms, that to double the diameter of the crater, the height must be increased by a factor of sixteen and to double the depth of the crater, the height needs to be increased by a factor of eight!


== Real Life Examples ==
== Additional Information ==


Impact craters on the moon, walking in the sand on a beach, water splashes, anything being dropped.
* For high school students, this demonstration would pair well with any videos or simulations of meteor impacts with the earth. That way, it helps them to see the increase in effect as the size of the object gets larger.
* You can ask students why the craters on the moon stay around, while any craters on earth do not. Encourage them to think about geological activity, such as earthquakes and volcanoes, or processes such as the water cycle and erosion.
* You can also try having an object drop into sand while in a vacuum, to show how collision with air affects the creation of craters.
* This demonstration is a part of the [[Astronomy Show]].

Latest revision as of 14:51, 25 March 2016

Astronomy: Crater Formation
Grade Range: Elementary School, High School
Format: Hands-on

The Crater Box is a simple way to show how craters form. This is an easy hands-on experiment that younger students will enjoy, if only because they get to throw balls in a sand box. This demonstration fits well into a high-school astronomy course, since you can demonstrate how to calculate the size of an object based on the dimensions of the crater it leaves behind.

Materials

  • A Large, Flat Box
  • A Mix of Coarse and Fine Sand
  • Small Balls of Varying Size and Mass
  • Yard Stick
  • Ruler (optional)


Safety Precautions

Please read the Physical Demonstration section of the Demonstration Safety page before performing this demonstration.


Demonstration

  1. Ask a student to drop one of the balls into the box, from about one foot above the sand. Let them drop a few different types of balls, so they can see how the mass of the ball affects the outcome.
  2. Ask the student to now drop a ball from two feet up. Can they see a difference in the depth of the crater? What about the width?
  3. Ask the student to now drop a ball from three feet up. Ask again if they can see a change in the width or depth of the crater.
  4. Optional: If students would like, they can use the ruler to measure the width and depth of the hole at the different heights. Do they see a trend forming?


Why This Works

Short Explanation

Crater formation is easy to see and understand. An object comes in from outer space, strikes a planet or moon, and that impact results in a hole on the surface. We can replicate this using this box of sand and set of balls, and look at what you need to make bigger craters.

When you drop the different balls in at different heights, you see that the more mass the ball has, the bigger the crater it makes. This is because the amount of energy our ball has depends on two things: how big it is, and how fast it is going when it hits the sand. Since we are dropping the balls instead of throwing them, we can have them all be moving at about the same speed when they hit the sand. This means that the only thing that changes the outcome is how much mass each ball has. In other words, the bigger and heavier the ball, the bigger the hole it will make!

We can see that the craters are all forming in similar ways, whether they are big or small. This is because craters have three stages of formation. The first stage is the Contact Stage, when the ball hits the surface. The second stage is the Excavation Stage, when some of the sand is sent flying by the impact, and we see the hole widen up from the ball's impact. The final stage is the Modification Stage, when we see the walls of the hole collapse a bit, and the flying sand lands again. The craters are not very big, however, and that is because it takes a lot of energy to make the sand move out of the way without scooping it. In fact, to double how wide the hole is you need to drop the ball eight times higher, and to double how deep it is you would have to drop the ball from sixteen times higher!

Full Explanation

Crater formation is easy to see and understand. An object comes in from outer space, strikes a planet or moon, and that impact results in a hole on the surface. However, the dimensions of the crater formed, and what factors into the dimensions of it, are a bit harder to comprehend.

When we drop a ball into the sand, and as we drop it from higher heights, we can see the three stages of crater formation happening. We first see what is called the Contact Stage, when it first strikes the surface. The ball will sink into the surface, compressing some of the sand, and creates a pressure wave in the sand itself. As this pressure wave travels out through the sand, it pushes some of the sand around the ball up and away from the impact. This is the Excavation Stage, when we see the bits of sand being flung up around the ball, and we see the crater's width form. Right after this we see the Modification Stage, when some of the sand forming the crater wall collapses into it, finishing the shape and size of the crater.

When we drop the ball from differing heights, we are affecting how much energy it has when it strikes the sand. In this case, we are looking at the relationship between Potential Energy (PE = mgh) and Kinetic Energy (KE = 1/2 mv^2); By increasing the drop height, we are increasing the final velocity of the ball, which affects the final dimensions of the crater. When a crater forms, the initial crater before any collapse will normally be spherical, and will have a depth and width that are proportional to the size of the object. If we measure the width and depth of the craters formed by the balls in the sand, we should start to see a trend that both of these factors are increasing. They both increase slowly, however, with the width of the crater growing faster than the depth of it. This is because of the spherical shape a crater takes on; the volume of a sphere can be calculated with a cubed diameter, and the crater formed will never have a volume greater than 1/3 of an imaginary sphere placed within it. We can combine these terms to find:

Diameter d1/3 ∝ 1/2 mv2 = mgh
Depth d1/4 ∝ 1/2 mv2 = mgh

If we want to see the crater from the two foot drop get twice as wide, we would have to drop it from eight feet high! Also, in order to see the crater get twice as deep, we would have to drop the ball from sixteen feet! If we drop objects from the edge of the atmosphere, however, they will reach a max velocity because of the air slowing it down. In that case, we would instead have to adjust the object's mass is in order to see larger craters. This is why little meteoroids falling to earth don't usually leave a mark, but bigger ones will!


Additional Information

  • For high school students, this demonstration would pair well with any videos or simulations of meteor impacts with the earth. That way, it helps them to see the increase in effect as the size of the object gets larger.
  • You can ask students why the craters on the moon stay around, while any craters on earth do not. Encourage them to think about geological activity, such as earthquakes and volcanoes, or processes such as the water cycle and erosion.
  • You can also try having an object drop into sand while in a vacuum, to show how collision with air affects the creation of craters.
  • This demonstration is a part of the Astronomy Show.
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