The first time you drop the ball the contact area is going to be small, essentially one point. Once it has crushed into the wood the contact area is larger, some portion of a sphere. So the next time you drop the ball the contact stress is going to be lower, so the ball won't indent as far on the second drop. So, I don't see that this experiment illustrates the phenomenon. However, I'll play with it to see if I can find a way to demonstrate (or not) the principle to myself. Phil F >Hi Phil. > >Take a nice piece of soft wood and drop a 100 gram steel ball on it from >say a 2 feet height. Measure very carefully the depth of the >indentation. Then repeat exactly the same drop in the same exact >place. Remeasure the depth. It most certainly wont be even half the >increase in depth as the first drop was. What the actual figures are for >any given type of wood I have no idea. But the principle in this case is >what is important. > >Cheers >RicB > >Phil writes: > >Another factor, of course, would be the wood getting stronger as it is >indented (work hardens, so to speak) - the phenomenon described by Ric >B. I've never seen any data describing this phenomenon.
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