This should imply the entropy of the rubber band has decreased, but how does the entropy of the whole universe increase here. Roussel department of chemistry and biochemistry university of lethbridge february 21, 2009 a rubber is a material that can undergo large deformations e. Exploring the thermodynamics of a rubber band david roundy department of physics, oregon state university, corvallis, oregon 97331 michael rogers department of physics, ithaca college, ithaca, new york 14850 received 27 february 2012. Most rubber bands are manufactured out of natural rubber or, especially at larger sizes, elastomer, and are sold in a variety of sizes. A resource for teachers a script for classroom demonstration illustrating dg dh tds.
The calculation involves the probability of finding the system with a given distribution of molecular configurations. First, stretch a rubber band and hold it in position for a few seconds. In rubber the elastic force is due to the thermal interactions of the molecules within the material. Pdv work must be done on the rubber band to stretch it, and. Following this a discussion of the applicability and the limitations of the theory is presented. A refrigerator that works by stretching rubber bands youtube. Thermodynamics of a rubber band, american journal of physics 31 5. Thermodynamics of rubber bands recommended for chapters. To measure partial derivatives experimentally and test the validity of the cyclic rule of partial.
Then measure the length of the rubber band within the marks just drawn. Gale rhodes department of chemistry university of southern maine portland, maine 041049300. Next, observe the ml beaker and convert the distance the rubber band could stretch from ml to cm. To determine how the entropy of a rubber band changes as the rubber band is stretched.
On stretching a rubberband does the entropy increase or decrease. Daniels department of physics, nc state university, 2401 stinson drive, raleigh, nc 277058202, usa dated. This are exercises that to accompany the textmap organized around raymond changs physical chemistry for the biosciences textbook. The odd behavior of rubber bands materials science and. The key lies in the reason for the stretchiness of the rubber band. Watch your teachers demonstration and answer the following. Dwrev3d pdv, and occasionally with work in onedimension. Thermodynamics of rubber bands university of california. In the following you will calculate the temperature and entropy change of stretching and. 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. Rubber heats up on stretching and cools on retraction. Second, and third laws of thermodynamics, energy minimization and entropy maximization, fundamental equations, intensive vs. The individual molecules that make up the rubber band are called polymers. An elastomer has rather unusual physical properties.
The rubber band was patented in england on march 17, 1845 by stephen perry. Rubber band thermodynamics a refrigerator powered by stretching rubber bands ok so its only a 2. So he observed that stretched rubber contracted on heating and elongated. Thermodynamics demonstration originally prepared for the coursera mooc. Adiabatic stretching of a rubber band physics forums. Statistical physics and thermodynamics physik freie universitat. And, in fact, if we apply a gas flame to a rubber band holding a weight, we will see that the band contracts abruptly fig. Fys2160, thermodynamics and statistical physics, fall 2019 due. 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 second law of thermodynamics is centered around the concept of. And entropy can be defined as lack of order in a system. According to this law, a system or body will move from a state of order to another state of disorder naturally.
My text says that on stretching, the arrangement of particles become m. Band heats on sudden stretching constant s entropy decreases on stretching molecules unfold. If we stretch slowly in air at room temperaure, we have a reversible, isothermal process with q professor of chemistry thermodynamics in two dimensions surface tension. In order to feel the heat from the rubber band the student needs to physically stretch the rubber band. Exploring the thermodynamics of a rubber band david roundy department of physics, oregon state university, corvallis, oregon 97331. A refrigerator that works by stretching rubber bands duration. August 3, 2015 abstract entropy is a di cult concept to teach using realworld examples. We are not stretching the actual polymer molecules, just sort of changing.
Rubber bands provide an appealing subject for a ther. Students stretch a rubber band from a hook in a stopper at the bottom of a glass tube to a chain connected to a force meter at the top of the tube. Rubber is an attractive choice for undergraduate education because simple and tractable thermody. Equation of state and molecular structure objective to determine the macroscopic thermodynamic equation of state of an elastomer, and relate it to its microscopic molecular properties. By using the following basic equations for helmholtz free energy and its discussion about entropy, the force generated from the deformation of a rubber chain from its. Abstract a thermodynamic study of an isotropic rubber band under uniaxial stress is presented on the basis of its equation of state.
Following this a discussion of the applicability and the. As the middle of the string moves, the ends of the. So it is true that when we heat a rubber band it pulls, and this fact is definitely related to the fact that when we release the tension of it, it cools. Then quickly release the tension and press the rubber band against your lips. Pdf the behaviour of rubber differs from that of conventional materials. Our case is an unsual presentation of the rubber band tied around the arm during native treatment of bone fracture causing superficial skin necrosis, circumferential scar and discharging sinus. Statistical thermodynamics of rubber rubber chemistry. The rubber bands grow warmer as they expand and cool as they contract. H is negative for stretching the rubber band and positive when the rubber band contracts. Entropy change stretching and contracting at constant t. The flory theory of rubber elasticity has pointed out the rubber elasticity has primarily entropic origins. Using the same effect, a stretched rubber band will contract on its own when heated. Place the rubber band flat on a table and mark two lines from where the rubber bands elasticity will be measured. The entropy change for the stretching of rubber is calculated by statistical methods, neglecting intermolecular attractions and deformation of bonds and bond angles.
The sample may be deformed in one direction as in stretching a rubber band in the zdirection, or in two directions as in simultaneously stretching a film in the x,y. By heating the rubber band, we increase the entropy. Does this mean a rubber band gets colder on stretching. Umr chemlabs thermodynamics of rubber elasticity pch 599 gary l. Release the tension on the rubber band and touch it to their upper lip, the rubber band will feel cooler. It is fundamentally different from the restoring force in a spring, which relies on the mechanical stiffness of the material. Have the students touch the rubber bands to their lips. In simple cases from which, tension in rubber is an effect of entropy. Students stretch precut rubber bands to their lips, stretch the rubber bands, and then allow them to contract. Since the stretching of the rubber band was an adiabatic change, there. Rubber as an aid to teach thermodynamics indian academy of.
Thermodynamics and equilibrium 145 here is a simple experiment. Heating the stretched rubber band causes segments of the molecules to move more vigorously, which can be represented by wiggling the middle of the string back and forth. Introduction we are all familiar with the very useful properties of such objects as rubber bands, solid rubber balls. The behavior of the rubber band is compared with both that of an ideal elastomer and that of an ideal gas, considering the generalized joules law as the ideality criterion.
Rubbers thermodynamic phenomenology is also often counterintuitive. Pdv work must be done on the rubber band to stretch it, and that work is given by. An equation of state relating the tension, length, and temperature of a rubber band is then derived. Exploring the thermodynamics of a rubber band oregon state. If f 0 when the band is pulling inward, then work f dl is done on the band when it is stretched through a distance dl0. In an effort to address these obstacles, we have developed a simple laboratory activity, the stretching of an elastic rubber sheet, intended to give students handson experience with the concepts of entropy, temperature and work in both adiabatic and quasistatic processes. When i stretch a rubber band, the fibers straighten out causing lesser randomness and more order. Bertrand, professor of chemistry thermodynamics in two dimensions surface tension.
Because most errors are due to ratedependent hysteretic and plastic effectswhich tend to be systematic, rather than. We can safely assume that the volume change of the rubber band is negligible for small stretches, in which case for an isothermal stretch. Pdf exploring the thermodynamics of a rubber band researchgate. It seems that on stretching a rubberband, entropy or the degree of disorder is likely to increase. Rubber band thermodynamics a refrigerator powered by. Dec 23, 2011 homework statement for a stretched rubber band, it is observed experimentally that the tension f is proportional tot he temperature t if the length l is held constant. A thermodynamic analysis of these two experiments can tell us something about the molecular structure of rubber. Second law of thermodynamics exercises chemistry libretexts skip to main content. Jun 05, 2017 entropy change stretching and contracting at constant t. Jan 27, 2016 thermodynamics demonstration originally prepared for the coursera mooc. The odd behavior of rubber bands thomas stoebe university of washington seattle, wa.
Heat is produced in the rubber band as it is stretched. Ask them to stretch the rubber band, then place it on their upper lip. To determine the number of polymeric chains per unit volume in a rubber band. To measure partial derivatives experimentally and test the validity of the cyclic rule of partial differentiation. Equivalently, we can say that the tension p depends on the length land temperature t. When a rubber band is stretched rapidly, heat is given off. Consider a rubber band under tension, f, with length per. Homework statement for a stretched rubber band, it is observed experimentally that the tension f is proportional tot he temperature t if the length l is held constant. Quickly stretch the rubber band and then press it against. The adiabatic contraction of the rubber band produced many more. C differential but it is a differential made by rubber band thermodynamics.
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