The physics of items sinking in the ground

[Rich jaws]

Have been doing a lot of detecting the past couple of months and have found a lot of clad and some silver and gold jewelry. Have found two large cent pieces and a number of wheats but no pre 1964 silver coins. Of course it depends on the type of soil, conditions, rainfall, temperature, etc. but does anyone else wonder what the sink rate of items would be in the soils they normally search. Just trying to understand the physics a little. It is a fascinating hobby metal detecting.

 

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[CoinHunterAZ]

I believe that the majority of items get covered up rather than sinking. Leaves, pine needles, and blown in dirt layers in over the top of stuff. In some areas around here there is a clay layer beneath the topsoil. I have found items just on top of the clay layer, usually 7-9" deep at most, but never below it. In some places I take a rake with me to remove detritus from the top so I can get to the actual dirt and increase depth a bit. There are areas along some old trails here that people used to camp beneath large trees. Several times when I have raked, I have found old bottles as well.

 

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[finderskeepers]

Working a site right now, where I've raked off 4" of detritus and pulled up 2"-3" layer of roots/rhizomes. Still concerned about depth as the site returned to forest over 100 years ago. Hope I can beat the ground freeze.

Yes, Coinhunter, nothing moves in that clay, including water. I'm lucky, not much of it up here at all.

 

[JackalopeZL1]

Physics, Gravity, mass and density have been proven. There are many factors that help a coin get deeper into the soil. Sinking is of or them

 

[ConceptualizedNetherlandr]

 

[RustyGold]

I wonder if earthquakes are another factor that cause the coins to sink lower into the dirt!
I'm almost sure vibrations from the pounding of the waves on the seashore helps items to sink further into the sand!

 

[Higgy]

I wonder if earthquakes are another factor that cause the coins to sink lower into the dirt!
I'm almost sure vibrations from the pounding of the waves on the seashore helps items to sink further into the sand!

Kind of like when panning for gold? Agitate the pan so all the heavies sink? Intriguing idea!

 

[maipenrai]

Since the sinking of coins in dirt has been mostly solved, what about the movement of coins at the beach? Everyone knows, that if you drop a coin or ring in the sand, it will be very hard to find, even when you know exactly where it was dropped, now where do the coins go in the surf? What kind of movement is there, horizontal and vertical?

 

[Treasure_Hunter]

I have to respectfully disagree with those of you who believe that coins don't sink. Coins and other objects absolutely do sink into the ground, and I will explain how.

If someone were to drop a penny into a glass of water what happens? It drops through the water and to the bottom of the glass. The reason this occurs is because the penny has mass, and gravity takes an effect on it. In a simplified explanation, as gravity pulls down on the coin, the molecules of water under it move out of the way, or displace, allowing the penny to sink to the bottom. This is a fairly simple concept.

Now drop a penny onto the ground. Of course it doesn't disappear into the ground right away because the dirt doesn't move out of its way. However, over time it does. Some folks theorize that rather than sinking, the coin gets buried as dirt and organic matter is deposited on top of it. Although this contributes to the coin disappearing into the ground, the more influential factor is that the ground beneath the coin does actually move, allowing the coin to sink.

So taking the same principles as the water example, in order for a coin to sink the molecules beneath it (in this case the particles of dirt), have to move out of the way. This does occur by a variety of means.

First of all, and the most powerful, is water. Put a coin on a patch of dry dirt. Now wait for it to rain. After the rain stops, pick up the coin. Obviously the dirt will be wet underneath it. This is because the water flowed under the coin. What happens when water flows? It erodes the ground and moves the particles of dirt. Whether it be rain or sprinklers, we have now begun the slow process of moving the dirt particles out from under the coin. The sinking process has begun.

Now enter grass. When grass or other plants grow, they produce roots. Roots extend into the ground and under the coin. The roots move (displace) the dirt so they can take up the space they need as they grow. Any mildly experienced detectorist has dug up a coin that had been encased in grass roots. Well eventually those roots under the coin die. Because plant material is mostly made of water, when that organic material dies it decomposes and reduces in volume. What is left is a void, or space under the coin, where this small root once was. So what happens? This minuscule hole collapses, allowing the coin to ever so slightly fall (aka sink).

Let's add some earth worms into the mix. Worms essentially eat dirt. They take in dirt, digest the organic material in it, and discard the rest. So when a worm burrows under a coin, it leaves yet another void (hole) in the ground. Eventually the mass on top of this void, be it the coin or otherwise, is pulled down by gravity and the hole collapses and fills in the void. Well the coin has now sunk just a bit more.

Now let's add rain and snow melt into the equation. The water seeps into the ground and by simple physics, it will flow into areas of lesser concentrations of dirt. Basically it will fill in those voids left by dead roots, worms, etc. And when water flows, it causes erosion. Dirt is moved which allows the coins to sink further into the ground.

This is why most coins, even the oldest of colonial ones, are typically found no more than ten inches deep. This first few inches is where there is the most activity in the ground occurs. The roots of grass and other foliage only grow so deep. When it rains, water only soaks so far into the ground. Worms and bugs eat organic material so they burrow only as far down as they need to find food. For these reasons, coins don't sink farther and farther into the ground over time. They do reach a limit because at some point there is very little occurring under the coin to cause the dirt to move. But they absolutely DO sink some over the years.

I mean no disrespect, but the jar example that Jason In Enid gave is flawed. Of course a coin dropped into a jar of wet dirt won't sink. But that jar and its contents aren't exposed to any environmental factors, such as weather, plant growth, etc.. A closed jar is a static environment. The real world is not.

If you still think that coins don't sink and instead are covered up over time, think about this. My family owns a house that was built around the turn of the century. I have hunted the property and have found many old coins along the cement walkway that leads to the house, as well as along the cement sidewalk in front of the house. These coins are routinely five or six inches deep, below the level of the sidewalk and walkway. So if you subscribe to the theory that coins don't sink, then it would have to be concluded that the sidewalk and walkway have raised up five or six inches over the years. And since the walkway to the house still meets the foundation of the house at the same place it did 100 years ago, then it would have to be concluded that the whole house has also raised up five or six inches over the years. And this was all occurring while the coin was staying in the same spot on the ground and just being covered up. Obviously this isn't what happened.

Water, plants and worms aren't the only factors that contribute to coins and other objects being able to sink into the ground. The freezing and thawing of the ground during the seasons can have an effect, as well as other things. But the bottom line is this: over periods of time and with the right conditions, coins do sink into the ground. The rate by which they do and the depth that they get is determined by a number of factors.

Very good post. Just like at the beach, items that are denser than beach sand sink into the sand.

“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[Treasure_Hunter]

Since the sinking of coins in dirt has been mostly solved, what about the movement of coins at the beach? Everyone knows, that if you drop a coin or ring in the sand, it will be very hard to find, even when you know exactly where it was dropped, now where do the coins go in the surf? What kind of movement is there, horizontal and vertical?

Lots of movement in the water. One year i recovered an engraved silver ring a mother gave her son for Christmas that was lost at least 50 yards from where I found it. It was lost in 3-4 ft surf with strong current running parallel to shore.

“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[DadOfTwo]

Physics, Gravity, mass and density have been proven. There are many factors that help a coin get deeper into the soil. Sinking is of or them

And disproven, in the case of gravity.

 

[Frankn]

OK, I almost got banned over this on TN years ago.
Objects do not sink in soil normally. Yes maybe a swamp or quicksand, but that involves water.
Objects are covered by layers of decayed organic material (earth).
There are other factors like erosion by wind or water.
If there is no decaying organic material (desert area) the item will remain on the surface. Wind or water can alter this factor.
I have seen items in the desert while prospecting that have probably been laying on the surfase for 100 years.
Now for the sinking density argument. All those dense Head stones are still up in the grave yards.

You can't tell when a coin was dropped by the date, but in my area with seasonal foliage dropping, You can get an idea by the depth.
Most coins dropped in my area in the 40's will be app.3"-4" down Items dropped 200 years ago will be app. 10" down, judged by actual finds.

The beach has it's own rules. A coin set on the sand will set there forever unless acted upon by an outside force like the ocean , people moving around, wind blown sand ,etc.

I had a good physics course in school, lol. Frank

 

[Rich jaws]

Decaying organic matter doesn't explain why that 2004 coin next to the cement path is 4 inches down while the cement path is still at the same height as the lawn. Using the decaying matter argument, wouldn't the cement path be below grade? I am convinced water plays a key role in the sinking coin combined with freeze/thaw, worm action and root action.

 

[Frankn]

Decaying organic matter doesn't explain why that 2004 coin next to the cement path is 4 inches down while the cement path is still at the same height as the lawn. Using the decaying matter argument, wouldn't the cement path be below grade? I am convinced water plays a key role in the sinking coin combined with freeze/thaw, worm action and root action.

I see you subscribe to all the popular missconceptions, lol I have gone by what I have see in the past 77 years and what I have been tought in physics.
You make an unbacked statement. How old is the cement path? Was the coin planted by a child? How high was the cement when it was installed. Is a grass catcher used when the grass is mowed. You see there are many variables. I just used basic facts backed up by actual experience, not one shot examples with no backup. Frank

 

[Rich jaws]

Sorry, I missed the "basic facts" in your unsupported conclusions. You state that where there is no decaying matter, items will remain on the surface although rain and wind can alter that factor. If there was no rain, no wind, no worms, no root activity in an area, of course items would remain on the surface. Just like the jar in the closet experiment described earlier in this thread. Under your theory, wouldn't the headstones also be getting covered by decaying vegetation? Perhaps all cemeteries use grass catchers? The reason headstones don't sink readily is likely primarily because of the relatively large surface area of the headstone against the ground. Coins dropped in the 40s will be 3-4 inches down? How can you possibly know how long ago items were dropped? All we can know with certainty is that the coin was dropped sometime after it's mint date. We can guess how long the coin was in actual use by its wear but nothing more. My whole point was that there are a lot of factors and variables involved, not just decaying vegetation.

 

[Treasure_Hunter]

I have also found fairly recent coins 4+ inches in ground in parks by picnic pavilions, and sidewalks that are 20+ years old..

“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[Frankn]

Sorry, I missed the "basic facts" in your unsupported conclusions. You state that where there is no decaying matter, items will remain on the surface although rain and wind can alter that factor. If there was no rain, no wind, no worms, no root activity in an area, of course items would remain on the surface. Just like the jar in the closet experiment described earlier in this thread. Under your theory, wouldn't the headstones also be getting covered by decaying vegetation? Perhaps all cemeteries use grass catchers? The reason headstones don't sink readily is likely primarily because of the relatively large surface area of the headstone against the ground. Coins dropped in the 40s will be 3-4 inches down? How can you possibly know how long ago items were dropped? All we can know with certainty is that the coin was dropped sometime after it's mint date. We can guess how long the coin was in actual use by its wear but nothing more. My whole point was that there are a lot of factors and variables involved, not just decaying vegetation.

Well Rich, I think it went by you so I will take one last point by point for you.
I liked the jar in the closet explanation. Basicly he is saying, ITEMS DON'T SINK IN THE GROUND which this post is supposed to be about.
Now for the head stones. I am talking about those old , tall, heavy headstones The point is they are still there where they were placed not sunken in the ground and they are a lot heavier and denser than coins. You don't have to complicate it by adding surface area. They have more pounds per square inch weight than coins.
My coin measurement came from a search of a 200 year old home lot. All coins found from the 40's were between 3" and 4" The ax head I found there was 10" down and was probably used to clear the lot 200 years ago. The house was built 200 years ago. I think I mentioned that other factors were involved.
Here's the house and some of the items mentioned. This is my last responce to you on this thread. I don't want to lock the guys thread. Frank
Note, I didn't show all the coins on this picture.

 

[Rich jaws]

Well Frankn, you obviously missed a lot of points I made. You can not simply ignore surface area when you are talking about things settling or sinking into the ground just as one can't ignore gravity. It all factors into the equation. You are simply speculating on how long those objects were in the ground and any conclusions based there on are nonsensical. Also, what is your conclusion with regard to the tombstones? What because the tombstones have more pounds per square inch than a coin they will not get buried by the decaying grass and leaves? Just trying to understand your thinking. Basing conclusions one one test case (one 200 year old house) is called bad science. Enough said.

 

[Treasure_Hunter]

Stop the insults ..

“A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed.”
― James Madison
The Constitution of the United States of America

 

[RustyGold]

Why do old tombstones lean? Is it because they have sunk a little? Or is that just the way they illustrate them in halloween cartoons!

 

[thumper]

Its hard to explain coin depth...i have dug a zinc cent at 9" and a merc dime at 3" within a foot of each other...who knows?