p.s. in point of fact, the pressure is a bit lower than the above formula, because of (and as I recall), essentially two things -- first the metal acting as a heat sync, second, because some of the coin squishes into the die making the area change over time. But those are relatively small factors, from what I understand of the physics. (It's been a long time since deformable bodies classes in college.)
Just to stress Leadfoot's answer (F = P * A or P = F / A) normal coin force = 400 tons (about right) coin area = 1 (a little smaller than a half) Pressure = 400 / 1 = 400 T/sqin Off center strike = 400 tons coin area = 0.5 pressure = 400 / 0.5 = 800 T/sqin
All of your physics note one solid push against another solid. No where does that forumla take into account a partial strike. You have 1/2 of the die(solid) striking 1/2 of the coin(solid). The other half of the die is striking empty space, which allows the metal to flow outward and move. The high heel is not the same example. In the case of the high heel you are reducing the size of the area, but not what it is striking(still solid). Think like this - you walking on a 1 foot high side walk nothing on the sides, each step is consistent. So your forumla works. Now put 1/3 of step on the side walk and 2/3 over the edge - what happens? You did not change the pressure of you step they are still consistent - but your ankle now rolls and off the side walk you go. So in the case of a coin not all of it is struck - not totally solid versus solid as the formula suggests. I just don't think it takes into account all the variables. So in my mind did the planchet move when first struck? What did the metal flow do? Not all off center strikes are well struck examples over the complete surface - or you would have complete rims. Were the dies worn? Were they lose? All of that will play into the strike on the coin. Now having said all that I do not dispute that weak struck coins or coins in general cannot have planchet flaws which Doug disputes. To me it is still how to tell the difference on some coins and if they should be ignored or not. Still neither side has won me over - yet.
Define solid. How about (from wiki, but it is what I learned); Somehow a coin just does not quite fit the definition of a solid during the minting process - at least not to me. Different materials change states under pressure/vacuum etc. As an "also", a step is not pressure, but a force. You take that force and divide it by the area and then you get pressure.
At no point during the minting process is the coin ever in a liquid state. Even the hardest alloys will demonstrate a measure of malleability under enough compressive stress. While it might serve as and interesting side discussion, the temperature increase of the planchet during the striking process is no where near the annealing temperatures much less the melting temperatures of the metals involved.
I won't get into the discussion of whether the coin is actually a solid or liquid. (I think you will find that point a little more debatable than you state.) However, I think you will agree that the laws of physics more resemble those of a liquid than a solid at those pressures. BTW, I am referring to high school physics, not special relativity physics.
Well I am not really arguing physics - just that this simple equation while true just will not always contain all the variables for a strong strike or not. I think even part strikes will still have die contact marks - maybe not on the high points but around the rims. Plus even for partial strikes planchets will not be 100% identical. So some will have strong strikes all over - no die marks as doug suggests, but to the die marks moved because of the off center strike and minute imperfections in the planchet. To me some are caused by the planchet and some by the dies and some by just not everything is always perfect in the world. Gee - did I just explain choas theory - I really agree with John - I hate that character. Bottom line - still not got an explanation that covers it enough to explain it. I am still seeing where both sides of the coin
easy: E=MC 2 no problem, just insert the #'s and solve the equation. as you will see the answer is obvious.
You guys are leaving something out of your equations to determine pressure. Consider - when a coin is struck normally, it is in a confined space. Now what happens when that same amount of force is applied to something that is not in a confined space ? Pressure is reduced. Every single time.
Of course there is a reason. The reason is because they believe in the genrally accepted idea. But the thing about generally accepted ideas is that they are sometimes proven to be wrong. And every single that happens it starts with 1 person disputing that idea.
Then just where does this force go if not into pressure?. Something has to resist this force, What? I would love to continue this, but I have grand kids and a zoo.
Easy, if the coin is dropped in a flat horizontal plane, what other part would you expect to come into contact with something except the high point ? Now that's just one way. Another way would be that the coin came into contact with something that had an unever surface and the high point of that uneven surface came into contact with the high point of the coin. That depends entirely on what it is that the coin is coming into contact with. Not all contact marks are caused by other coins. Wear shows on the high points first because when the coin is laying flat on a surface (which it usually is) only the high points touch that surface, assuming that surface is flat and smooth, which it usually is. You might think so, but there are several other perfectly reasonable explanations as well, not just one. Another is that the high point is the most likely to come into contact with any other surface, just like wear does. Exactly !
That is true, sometimes. The times it is true is if the contact mark is newer than the rest of the surface of the coin. But if a contact mark is old, then the exposed metal inside the contact mark will have just as much time to tone as the rest of the surface of the coin does. And then it will not look fresh. Also, as I said previously, not all contatc marks are caused by other coins, which have sharp edges. Some contact marks can be caused by surfaces or objects that do not have sharp edges. And those marks will not look "sharp". You can assume that might be the reason - but that doesn't mean that it is.
Yes, there is a subtle difference in the luster of a not fully struck area. And if you look at the examples I have posted you can see those differences on the highest points. Which proves that the struck areas have a weak strike.
It's not that something does not resist the force - it is that the pressure is never created to begin with. A coin planchet is a compressable object. And pressure only reaches its maximum, and it is the pressure that creates a full strike not the force, when that object is compressed within a confined space. The confined space is defined by the dies and the collar. The planchet is trapped betwen these 3 things. And when force is applied to the planchet in that confined space, the planchet is squished, compressed. And when it is compressed the pressure increases because it cannot escape. The metal cannot flow beyond the confined space so the pressure inside that space increases. It can do nothing else. But apply that same amount of force to the planchet when it is not in a confined space, which it cannot be if it is an off center strike because the collar is not there confining it, and the pressure only reaches a fraction of what it does when there is a confined space. And with reduced pressure, the coin cannot be fully struck.
Here is my unscientific graphic showing one reason why off center strikes will indeed have strong stikes on the main design. when the dies come together you can bet they will not come down even with that much preasure with the planchet not being centered. the design to the center of the die should be fully struck with aurguably more preasure. The dies will not come down flat, they will flex at an angle.
You are ignoring the fact, not opinion fact, that equal pressure cannot be achieved because there is no confined space for the pressure to build in.
After reading this again, I'm still in the camp that total "plastic deformation" has not occurred 100% to eradicate marks that the surface of the planchet received during fabrication and in no how, no way those characteristic occurred out side the Mint. The grading should not be intimidated by these areas on the high points of coins because they left the Mint facility struck "as is" and is just part of the over all characteristics of a normal procedure.
OK, I understand where you're coming from. Always have. But if what you say is true, then why do we not see similar marks on every single weakly struck coin there is ? Now the Jefferson nickel is a wonderful example of this because just about every one ever struck is weakly struck.
