>Hunh? When was thelast time you compressed a spring by >hand??? Never. I just make this stuff up because it's sure to annoy someone. > Everyone I've ever compressed definitely >offers more resistance ( stiffness) the further it is >bent, or compacted. > Twoing Resistance (which is a force) is not stiffness (which is a mechanical property), in my definition of the terms. Stiffness is spring rate, or the amount of load required to cause a unit of deflection. If a spring (or a beam, or a soundboard) has a linear spring rate, then it takes twice as much load to deflect it twice as much, three times as much load to deflect it three times as much, etc. You have to put on more load to get more deflection, but the stiffness is not changing. Most common coil springs, made from wire of constant diameter, with coils at a constant spacing, have a linear spring rate within their working range. If you take one between your fingers and squeeze it you'll have to put on more and more load to compress it more and more. That doesn't mean it's getting 'stiffer'. If it takes 5 lbs to deflect your spring 1/4 inch, then the spring rate (or stiffness) is 20 lbs/in. So, it will take 10 lbs to deflect the spring 1/2 inch and 15 lbs to deflect it 3/4 inch. You have to increase the load or force on the spring to squeeze it down, but the spring rate is not changing. If you don't believe that, it's easy enough to demonstrate for yourself. Take a coil spring and an accurate gram-scale. Take a ruler or other measuring device with evenly space units on it - tape it or stick it to a block of wood or other support so that it will stand up on its own. Place the spring and the block with the ruler on the gram-scale. Zero the scale. Push the spring down some measurable amount on the ruler that would be within the normal working range of the spring. Note the reading on the gram-scale. Push the spring down so that the deflection on the ruler shows twice what it was when you took the first reading. Note the reading on the gram scale. It should be twice what the first reading was. It's taking more force to push the spring down farther, but the spring rate (load divided by deflection) has not changed. Phil Ford
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