To represent the concept of ammonite buoyancy, the model will operate on an up and down mechanism. The ammonite will move and up down corresponding with its weight because of a spring. The effectiveness of this system depends on the type of spring, and how the model interacts with it.
What type of spring should I use?
Compression and extension springs = compressed/extended linearly which creates a force that opposes that motion.
For this model, a compression spring would be most effective. The model will be able to stay down when the puzzle pieces are inserted, and rise back again once they are taken away. The spring will also fit into the tubing which will act as a stand for the model.
Hooke’s Law (Elasticity. Torsion. Force)
F = -kX
F = force applied to spring
X = displacement of spring
K = spring constant (stiffness)
Springs have certain stiffness to them which dictates the amount of displacement that they will endure when a force is applied (Hooke’s Law). Choosing the correct stiffness will be vital for the model as it needs to be soft enough so that the puzzle pieces affect the weight of the model and make it sink. It must also be stiff enough so that the model can rise up again once the puzzle pieces are taken out.
The spring will also need to have high strength to avoid creep – very slow plastic deformation over time. Enough strength in the spring will reduce maintenance needs.
The ammonite will be attached to the spring using mirror fixings. This means the model will be able to be taken off the stand if needed for presentation etc. It also makes repair work easier – if the spring deforms over time and needs replacing, the model can simply be detached and the spring slid out from the tubing and replaced.
In summary, the vertical motion of the ammonite rising and falling is created through a spring mechanism that operates based on changes in weight. The mechanism is simple and requires minimal maintenance. Ultimately, the mechanism grants opportunity for interactivity with the model while representing the concept of buoyancy.