Attractive restoring force

Pulling the atoms apart results in the development of an attractive restoring force between them that tends to pull them back together. The opposite is true if one tries to push the atoms together. 

In the usual situation illustrated in Fig. XIII-6 the particle is supported at a liquid-air interface against gravitational attraction. As was seen, the restoring force... 

This lowering of frequency of 250—500 cm-1 as a result of bridge formation is caused by the restoring force of the normal OH bond being reduced by the attraction acting in the opposite direction due to the acceptor atom of the bridge. 

Elastomers. Elastomers are polymeric materials with irregular structure and weak intermolecular attractive forces. Elastomers are capable of high extension (up to 1000%) under ambient conditions. That is, they have the particular kind of elasticity characteristic of rubber. The elasticity is attributed to the presence of chemical and/or physical crosslinks in these materials. In their normal state, elastomers are amorphous, and as the material is stretched, the random chains are forced to occupy more ordered positions. Releasing the applied force allows the elongated chains to return to a more random state. Thus, the restoring force after elongation is largely because of entropy. (Fig. 14.3)... 

The release techniques discussed here do not prevent adhesion from occurring during micromachine operation. Microstructure surfaces may come into contact unintentionally through acceleration or electrostatic forces, or intentionally in applications where surfaces impact or shear against each other. When adhesive attractions exceed restoring forces, surfaces permanently adhere to each other causing device failure—a phenomenon known as in-use stiction. ... 

The potential function in figure A1.2.1 has several cmcial characteristics. It has a minimum at a certain value Rq of the intemuclear separation. This is the equilibrium intemuclear distance. Near i Q, the function V(R) rises as R increases or decreases. This means that there is an attractive mechanical force tending to restore the nuclei to Rq. At large values of R, V(R) flattens out and asymptotically approaches a value which in figure Al.2.1 is arbitrarily chosen to be zero. This means that the molecule dissociates into separated atoms at large... 

The spring constants as well as the retardation constants of the polymer materials will be temperature dependent. Molecular excitation by heating will produce easier bending of the bonds in the chains. In addition, the expansion of the structure will increase the average spacing between the atoms of the structure which will weaken the restoring forces produced by polar and Van der Waals attraction effects. 

Figure 3.26. Force-separation curve, as in Fig. 3.25, with jump-in and jump-out shown for a cantilever of given spring constant. The dashed line is the restoring force for an oscillating cantilever, rest position r, which always exceeds the attractive force.

This case is relevant to an oscillating cantilever, as in IC-AFM. Figure 3.26 shows the case where the fixed position is at a far distance, and the restoring force always exceeds the attractive force, even though the spring constant of the cantilever is low. The oscillating tip does not jump in or out of contact. 

Figure 3.3 Parallel plate electrostatic actuator with a mechanical spring that provides a restoring force F in opposition to the attractive electrostatic force The initial gap is go-...

The top plate of capacitor Ci has been released and the bottom plate is fixed in position. The spring provides a mechanical restoring force to the attractive electrostatic force when a voltage Vs is applied. Both the top and bottom plates of capacitor C2 are fixed. 

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