Pulling forces

By applying a pulling force at a portion of the solute molecule in a specific direction (see chapters of Eichinger et al. and Schulten in this volume), conformational transitions can be induced in specific directions. In order to reconstruct information about the underlying potential function governing protein motion, the irreversible work performed on the system by these forces must be discounted ([Balsera et al. 1997]). 

Fig. 4. Typical AFM rupture experiment (top) Receptor molecules are fixed via linker molecules to a surface (left) in the same way, ligand molecules are connected to the AFM cantilever (right). When pulling the cantilever towards the right, the pulling force applied to the ligand can be measured. At the point of rupture of t he ligand-receptor complex the measured force abruptly drops to zero so that the rupture force can be measured.

Traction is typically used to align a bone by a gende, constant pulling action. The pulling force may be transmitted to the bone through skin tapes or a metal pin through a bone. Traction may be used as a preliminary treatment, before other forms of treatment or after cast immobilization. 

It should be recognized that tensile properties would most likely vary with a change of speed of the pulling jaws and with variation in the atmospheric conditions. Figure 2-14 shows the variation in a stress-strain curve when the speed of testing is altered also shown are the effects of temperature changes on the stress-strain curves. When the speed of pulling force is increased, the material reacts like brittle material when the temperature is increased, the material reacts like ductile material. 

We conducted spindle-severing experiments in the wild-type one-cell stage C. elegans embryo to investigate whether extra-spindle pulling forces participate... 

Nurse With respect to the astral microtubules emanating towards the cortex, which are shorter in the gyg-8 mutant, are the pulling forces a consequence of the microtubules in wild-type being attached to the cortex, or are they due to attachment sites in the cytoplasm and associated motors, which means that if you extend longer into the cortex you would have a bigger pulling force than if you are shorter ... 

Fig. 5. Monte-Carlo simulation of the stretching of a chromatin chain. A 100 nucleosome chain with 200 bp repeat and 11 bp linker DNA was first equilibrated and then exposed to a pulling force as indicated below the drawings. For displaying the full chain, the scale of the picture was changed with increasing force. An unwinding of the chromatin fiber and sliding of the nucleosomes can be readily observed.

A pulley consists of a wheel with a grooved rim in which a pulled rope or cable is run. Pulleys are commonly used with ropes or steel cable to change the direction of a pulling force or to add mechanical advantage. 

Pulleys are often used to lift things. For instance, a pulley could be attached to the ceiling of a room. A rope could be run from the floor, up through the pulley, and back down to a box sitting on the floor. The pulley would allow you to pull down on the rope and cause the box to go up. That is, the pulley causes a change in direction of the pulling force. 

You may have seen pulleys used in a warehouse to lift heavy loads. Another use for a pulley is on a large construction crane. The cable extends from the object being lifted up to the top of the crane boom, across a pulley, and back down to the electric winch that is used to pull on the cable. In this situation, the pulley again causes a change in direction of the pulling force, from the downward force of the winch that pulls the cable to the upward movement of the object being lifted. 

The key to solving spring problems is to draw a diagram of the arrangement, if one isn t already provided, and follow the pulling force through the system. 

When three identical springs are arranged in series and a pulling force of 10 pounds is applied, the total stretch is 9 inches. If these same three springs were arranged in parallel and the same 10-pound force were applied to the new arrangement, what would be the total distance of stretch ... 

If a subcooled (below the boiling point) liquid at point A is expanded isothermally, it will boil at point B ordinarily. However, if the liquid is of good purity and its container is not contaminated, it is easy to proceed along the line toward C. Such a liquid is then under tension that is, an external, mechanical pulling force is being resisted by the liquid. Numerous investigators have demonstrated the existence of liquids in... 

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