According to this law, a system or body will move from a state of order to another state of disorder naturally. Next, consider the difference between a stretched polymer and a relaxed polymer. Jan 04, 2018 however, rubber bands actually have a very good reason for being stretchy, and the full explanation relies on thermodynamics. Pdf exploring the thermodynamics of a rubber band semantic. Materials such as these, which are capable of undergoing large. Physics isa stretching rubber band free pdf file sharing. Exploring the thermodynamics of a rubber band oregon state. H is negative for stretching the rubber band and positive when the rubber band contracts. The key lies in the reason for the stretchiness of the rubber band. To determine how the entropy of a rubber band changes as the rubber band is stretched. Flir ir thermal imaging camera showing how a rubber band will cool below ambient temperature when stretched, held until it cools back down to ambient, and th.
Pdf exploring the thermodynamics of a rubber band researchgate. Theoretical background the thermodynamic identity for a rubber band is du. Comparison with ideal gas compressions a go over the sample problem on the thermodynamics of stretching a rubber band. An example of such a material is natural rubber, obtained from the plant hevea brasiliensis. Ppt the thermodynamics of a rubber band powerpoint.
In fact, it is this crosslinking that help the rubber band retain its shape after being stretched out. Heating causes the rubber band to contract, and cooling causes expansion. It as nothing to do with with adiabatic expansion because there in no expansion. It has to do with the tension in a rubber band and the work required to stretch or compress the rubber band. Rubber bands, the second law of thermodynamics, and entropy. Rubbers thermodynamic phenomenology is also often counterintuitive. Rubber band thermodynamics module 8 university of minnesota chemistry 4501. Thermodynamics of a ru bber band in this lab, we will measure the tension of a rubber as a function of length. Next, observe the ml beaker and convert the distance the rubber band could stretch from ml to cm. Chem 4501 introduction to thermodynamics, 3 credits kinetics, and statistical mechanics module number 8active learning answers and optional problemssolutions 1. The frozen rubber bands were just the opposite with the shortest length of 52cm, and were able to sustain the greatest amount of force of 33. By making this measurement at several di erent temperatures, we will be able to use a maxwell relation to determine the change in internal energy uand entropy sfor a rubber band that is stretched at xed temperature. The stretching of the rubber band is an isobaric expansion a b that increases the energy but reduces the entropy this is a property of a rubber bands due to rubber elasticity. So, if we stretch a rubber band, the work will be w fl,tdl l 1.
According to this law, a system or body will move from a state. Warm up a hair dryer, and then aim it at the rubber band. Think of it this way, when an elastic polymer is in its relaxed state, these molecules are all tangled up with each other and have no particular direction to them, but when you apply a force, i. Gale rhodes department of chemistry university of southern maine portland, maine 041049300. For an elastic rubber band of length lt,p at temperature t and under a. Theory of rubber elasticity thermodynamics, statistical mechanics and chain statistics kelvin, kuhn, guth, mark, james, treloar and flory second law of thermodynamics. Materials such as these, which are capable of undergoing large reversible extensions and compressions, are called elastomers.
Is there any temperature change as the rubber band is stretched and allowed to contract. Then measure the length of the rubber band within the marks just drawn. By utilizing the thermal properties of the rubber band, then a lot of research is made to study rubber bands as material conversion of heat engine to change heat to mechanical energy 2 345. Thermodynamics at work stretching a rubber band 1 stretch a rubber band quickly then hold it, still stretched, against your lower lip. The rubber band obeys the thermodynamic relations that are analogous to those of a gas. Then summarize briefly 1 the analysis of the reversible work of stretching the band at different t that tells us a how the free energy changes with length aaal at each t and. Adiabatic stretching of a rubber band physics forums. Article exploring the thermodynamics of a rubber band. The entropy change for the stretching of rubber is calculated by statistical methods, neglecting intermolecular attractions and deformation of bonds and bond angles. Using the same effect, a stretched rubber band will contract on its own when heated.
Pdf thermodynamics of rubber elasticity jose manzanares. Fys2160, thermodynamics and statistical physics, fall 2018. The deformation of a surface involves twodimensional. Features like loops in the relaxed state are indicative of larger degeneracy. So, a stretched rubber band has less disorder than a relaxed one. To examine and explain the effect of temperature on elastomers. Then summarize briefly 1 the analysis of the reversible work of stretching the band at different t that tells us a how the free energy changes with length aaal. Thermodynamics and equilibrium 145 here is a simple experiment.
Each spoke is cut, and the ends remaining on the wheel are bent into hooks so the rubber band can be looped around them. Place the rubber band flat on a table and mark two lines from where the rubber band s elasticity will be measured. Science and education temperature changes in adiabatic stretching the entropy s of a rubber band at constant volume can be evaluated, by using eq 1 and maxwells relation. Aug 15, 20 quickly stretch the rubber band out, and keep it stretched. Mark the maximum stretch length of the rubber band.
The thermodynamics of a ru bber band 1 the thermodynamics of a ru bber band. The odd behavior of rubber bands materials education matedu. Article exploring the thermodynamics of a rubber band id. Pdv work must be done on the rubber band to stretch it, and that work is given by. We can safely assume that the volume change of the rubber band is negligible for small stretches, in which case for an isothermal stretch.
Another surprising phenomenon is that a rapidly stretched rubber band will heat up, while a stretched band that is suddenly released will cool to below the. A spontaneous process is a process that occurs without outside intervention. The heated rubber bands were most elastic, stretching to the farthest distance of 69. The whole subject of thermodynamics depends essentially upon the following kind of consideration. Rubber bands provide an appealing subject for a ther. In classical physics, work is equal to force times distance. The crosslinks keep the polymers tied together in spite of them. Materials box of large rubber bands procedure hand out rubber bands to the class. Dec 20, 2012 we describe an upperdivision experiment in thermal physics where students measure the tension of a rubber band as a function of temperature and length and use a maxwell relation to find the change in internal energy and entropy for an isothermal stretch. This investigation would fit into units on thermodynamics and polymers. Rubber s thermodynamic phenomenology is also often counterintuitive.
Stretch a rubber band and allow it to contract while it is in contact with your upper lip. Aug 03, 2015 rubber s thermodynamic phenomenology is also often counterintuitive. By heating the rubber band, we increase the entropy. To test this, stretch a rubber band and press it to your forehead, lip, or wrist. The stretching was so rapid that heat transfer to the surroundings was negligible. In order to feel the heat from the rubber band the student needs to physically stretch the rubber band. In the following you will calculate the temperature and entropy change of stretching and. The rst law of thermodynamics for an in nitesimal reversible deformation. We describe an upperdivision experiment in thermal physics where students measure the tension of a rubber band as a function of temperature and length, and use a maxwell relation to find the change in internal energy and entropy for an isothermal stretch.
We are all familiar with the very useful properties of such objects as rubber bands, solid rubber balls, and tires. The results were pretty consistent, providing a reliable conclusion to the project. The frozen rubber bands were just the opposite with the shortest length of 52cm, and were able to sustain the greatest. An interesting effect of rubber bands in thermodynamics is that stretching a rubber band will produce heat press it against your lips, while stretching it and then releasing it will produce an endothermic reaction, causing it to. L 2 we have to pull to stretch the rubber band, which. This allows students to experimentally check the predictions of the entropic spring model for elastomers and observe that the entropy does indeed decrease as a rubber band is. A resource for teachers a script for classroom demonstration illustrating dg dh tds. If this is true, rubber without hysteresis must obey the laws of thermodynamics. Summarize relevant thermodynamic concepts using pedagogical example stretching a rubber band then discuss how. To measure partial derivatives experimentally and test the validity of the cyclic rule of partial differentiation. Statistical thermodynamics of rubber rubber chemistry and. The variables involved are fthe tension of the rubber band measured in newtons lthe length. Holding the rubber band in tension at ambient temperature is an. The rubber band experiment can be modeled as a thermodynamic cycle as shown in the diagram.
Watch rubber band to see if it will stretch spontaneously. Ask them to stretch the rubber band, then place it on their upper lip. The internal energy of the rubber increases because you have done work on the rubber band when you stretched it. Rubber band thermodynamics this problem deals with an extension of ideas that you learned in class about equations of state and work. Stretch the rubber band with both hands, and then quickly place it against your forehead. When the elastic band is not stretched, these molecules are all tangled up with each other and have no particular direction to them, but when you stretch the elastic they all become lined up with one another, at least to some. The spokes on a bicycle wheel rim are replaced with rubber bands. Stretching a rubber band a restoring force f is present when a rubber band is stretched to be longer than its equilibrium lengthfor modest displacements, f is a constant independent of length l. The odd behavior of rubber bands materials education. Examining a rubber band rubber is a long chain of polymerized isoprene monomers chain can stretch compress upon thermal changes changes in internal energy and entropy rubber contracts with heat, increasing force expands with cooling. But, bottom line, show that a rubber band should heat if you stretch it suddenly kids, do try this at home. Entropy change during stretching of a rubber band youtube. Chem 4501 introduction to thermodynamics, kinetics, and.
When we stretch the rubber band it heats up due to viscous friction of the molecules sliding over each other as we stretch the object. An elastomer has rather unusual physical properties. Is the contraction of a rubber band a spontaneous process. What happens if you release the stress applied to a crosslinked coil. Stretching and contracting a rubber band 1 take a rubber band which is about 5 mm wide, stretch it and allow it to contract. Exploring the thermodynamics of a rubber band public deposited. Some of that work went into changing the potential energy of the band while some went into heat. Thermodynamics temperature affects the elasticity of a rubber band in an unusual way. Entropy of a rubber band department of chemistry university of. By stretching the rubber band, you had to apply a force through a distance, i. A little more free energy, then thermodynamics of rubber, proteins. Add weights to the bucket, weights that are heavy enough to stretch the rubber band use whatever is available. A heat lamp is placed near one area of the rubber bands.
Amsterdam, 32, 1235 1929 it was shown that the heating effect which takes place in stretched rubber must be due to hysteresis, because from thermodynamic considerations it is obvious that a substance with a positive coefficient of elongation shows a cooling effect. To examine and explain the effect of temperature on elastomers rubber bands introduction. The calculation involves the probability of finding the system with a given distribution of molecular configurations. When a rubber band is stretched rapidly, heat is given off. To determine the number of polymeric chains per unit volume in a rubber band. A simple cartoon contrasting a polymeric solid in both a stretched and relaxed state. Exploring the thermodynamics of a rubber band exploring the thermodynamics of a rubber band david roundy department of physics, oregon state university, corvallis, oregon 97331 michael rogers filename. Thermal expansion caused the rubber bands to react as they did. Rubber band thermodynamics general chemistry, ch102 spring 2011 1. Roussel department of chemistry and biochemistry university of lethbridge february 21, 2009 a rubber is a material that can undergo large deformations e. Pdv work must be done on the rubber band to stretch.
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