Rubber band stretch experiment

There is an interesting demonstration experiment that you can do with a rubber band, preferably a large and/or thick one. Touch the unstretched rubber band to your lips. Then, stretch the rubber band... 

Design your first experiment to observe whether heat is given off or absorbed by a rubber band as it is stretched. Have your teacher approve your plan. 

Use the remaining items in the list of materials to design a third experiment to test what happens to a stretched rubber band as it is heated. Have your... 

You can easily perform the following experiments with a rubber band that is at least 0.5 cm wide. Quickly stretch the rubber band and then press it against your lips. You will feel a slight warming effect. Next, reverse the process. Stretch a rubber band and hold it in position for a few seconds. Then quickly re-... 

The experiment can be adapted in a simplified manner to everyday life We touch a thick rubber band with the upper lip and after waiting a short while for equalization of temperature, it is stretched quickly and powerfully and immediately pressed again against the upper lip. The band feels noticeably warm. When the stretched band is allowed to contract to its original length and then quickly pressed against the upper lip, there is a noticeable cooling. 

Suppose you stretch a rubber band, (a) Do you expect the entropy of the system to increase or decrease (b) If the rubber band were stretched isothermaUy, would heat need to be absorbed or emitted to maintain constant temperature (c) Try this experiment Stretch a rubber band and wait a moment. Then place the stretched rubber band on your upper lip, and let it return suddenly to its unstretched state (remember to keep holding on ). What do you observe Are your observations consistent with your answer to part (b) ... 

In all the experiments shown in figure 4 the injected polymer seemed to remain intact over the entire length of the test section and it is believed that they formed an elastic network. This conclusion was confirmed by an experiment in which the discharge of water was abruptly stopped. For several meters from the injection point the polymer strands were seen to relax like a stretched rubber band. 

It is essential to note that elastomers do not always behave in the manner known from stretching a rubber band at room temperature. Some of us might have seen an experiment when such a rubber band was put into liquid nitrogen, became brittle, and when stretching was attempted the band broke into little fragments. Thus, in general the type of behavior of an elastomer depends on the temperature. This is shown in Fig. 24.25 the elastic modulus E (for a certain fixed time after the imposition of a force) as a function of temperature T. At low temperatures we have the brittle behavior—as the rubber band in liquid nitrogen ... 

John s stretching vs temperature experiments were shown to be reversible i.e., a stretched rubber band contracted when heated and elongated when cooled. When thermometers which were as sensitive as John Gough s lips became available in 1859, Joule quantified Gough s experiments. John also showed that a stretched rubber band lost much of its elasticity when placed in cold water but this property was recovered when the water was heated. 

A strip of rubber warms on stretching and cools on being allowed to contract. (This experiment can easily be confirmed by a student using a rubber band. The rubber is brought into contact with the Ups and stretched rapidly, constituting an adiabatic extension. The warming is easily perceived by the temperature-sensitive lips.)... 

Equation (9.15) implies that you can get the entropic component of the force, dSld )T, from a very simple experiment. Hold the rubber band at a fixed stretched length T (and constant pressure) and measure how the retractive force depends on the temperature (see Figure 9.1). The slope of that line, (df jdT)(, will give - (dSld )r. The positive slope in Figure 9.1 indicates that the entropy decreases upon stretching. 

Everyday experience with common liquids teaches us that they have no preferred equilibrium configuration so that, at rest, they take the shape of the container they happen to be in. if we stir such a fluid, the drag will depend on how rapidly it is stirred and not on how much we deform it (e.g. how many revolutions one stirs). Conversely, the resistance one feels in stretching a rubber band depends on how far it is stretched and not on how fast this is done. Furthermore, there is a preferred shape — the unstretched length — that the material likes to return to. 

There is an interesting demonstration experiment that you can do with a rubber band, preferably a large and/or thick one. Touch the unstretched rubber band to your lips. Then, stretch the rubber band rapidly and immediately, retouch it to your lips. The rubber band will be warmer. This motion creates a thermodynamic cycle in which the system goes through a series of different states and then returns to its original state. The cycle acts as a heat engine. 

Fourier transform infrared spectroscopy (FTIR) has emerged as a valuable tool for rubber analysis. Siesler monitored the onset, progress and decay of strain-induced crystallization of a sulfur-cured NR during a cyclic experiment. The infrared absorbance of NR at 1126 cm assigned to C-CH3 in-plane deformation vibration is a band sensitive to crystallinity. A thickness reference band was taken to be the 1662 cm one assigned to v(C=C) stretching. The ratio of the absorbance bands at 1126 cm and 1662 cm revealed the reversible nature of strain-induced crystallization of NR. 

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