So, my question is. If, for example, I use a four-legged stool to set my subject on (a flower) and the camera is on a tripod. The tripod does not seem to vibrate, but he stool does.
What could I place under the four legs of the stool to dampen vibrations?
Why not just put the flower pot on another tripod if the camera on the tripod is not vibrating?
If you put a weight on a spring, then stretch the spring, then let it go, the weight bounces up and down, a little less each time, and eventually stops. That is damping. The time it takes to stop is related to the mass (the heavier the quicker it stops) and the stiffness (= elastic modulus) of the spring (the stiffer the quicker it stops). So making the stool heavier or of stiffer material - steel rather than wood, eg - will damp the vibrations better.
But if the vibrations are, eg, from nearby trains or trucks and reaching your floor through the earth damping will help but is not enough, because the vibrations do not happen in an instant and then decay. You need uncoupling, as Bjorn says (which is probably why the tripod is not vibrating: it is very stiff and poorly coupled to the floor).
Uncoupling, however, is a bit counter-intuitive. It requires that the vibrations cross
boundaries between materials of different density. It is not that soft material, such as rubber, "absorbs" the vibrations, it is that they are lost at the interfaces between the light and heavy materials. The loss depends on the difference in density, so steel on either side of rubber is
much better than concrete either side of rubber, which is a poor choice because concrete is usually only a little denser than hard rubber. Steel either side of bubble wrap is excellent. Because only the interfaces matter it does not matter how thick the layers of material are: thin metal sheets are as good as thick ones and one layer of bubble wrap is as good as several - but many interfaces with different densities is many times better than one.
