The individual molecules that make up the rubber band are called polymers. 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. This thermodynamics makes the rubber band gradually breach the skin and remain in the planes of the limbs depending upon the place and its position. 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. It is fundamentally different from the restoring force in a spring, which relies on the mechanical stiffness of the material. Heat is produced in the rubber band as it is stretched.
Adiabatic stretching of a rubber band physics forums. To measure partial derivatives experimentally and test the validity of the cyclic rule of partial. Jan 27, 2016 thermodynamics demonstration originally prepared for the coursera mooc. Rubber heats up on stretching and cools on retraction. 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. First, stretch a rubber band and hold it in position for a few seconds. 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. The rubber bands grow warmer as they expand and cool as they contract. Band heats on sudden stretching constant s entropy decreases on stretching molecules unfold. When a rubber band is stretched rapidly, heat is given off. This are exercises that to accompany the textmap organized around raymond changs physical chemistry for the biosciences textbook. Equivalently, we can say that the tension p depends on the length land temperature t.
A resource for teachers a script for classroom demonstration illustrating dg dh tds. Gale rhodes department of chemistry university of southern maine portland, maine 041049300. The adiabatic contraction of the rubber band produced many more. And entropy can be defined as lack of order in a system.
Pdf the behaviour of rubber differs from that of conventional materials. 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. Rubber band thermodynamics general chemistry, ch102 spring 2011 1. To determine the number of polymeric chains per unit volume in a rubber band. According to this law, a system or body will move from a state of order to another state of disorder naturally. Because most errors are due to ratedependent hysteretic and plastic effectswhich tend to be systematic, rather than.
In simple cases from which, tension in rubber is an effect of entropy. Abstract a thermodynamic study of an isotropic rubber band under uniaxial stress is presented on the basis of its equation of state. Abstract the entropy change for the stretching of rubber is calculated by statistical methods, neglecting intermolecular attractions and deformation of bonds and bond angles. We can safely assume that the volume change of the rubber band is negligible for small stretches, in which case for an isothermal stretch. Introduction we are all familiar with the very useful properties of such objects as rubber bands, solid rubber balls. 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. A refrigerator that works by stretching rubber bands duration. Rubber is an attractive choice for undergraduate education because simple and tractable thermody.
Thermodynamics of rubber bands university of california. Daniels department of physics, nc state university, 2401 stinson drive, raleigh, nc 277058202, usa dated. August 3, 2015 abstract entropy is a di cult concept to teach using realworld examples. Ask them to stretch the rubber band, then place it on their upper lip. 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. It seems that on stretching a rubberband, entropy or the degree of disorder is likely to increase. Statistical physics and thermodynamics physik freie universitat. Second law of thermodynamics exercises chemistry libretexts skip to main content. To determine how the entropy of a rubber band changes as the rubber band is stretched. Does this mean a rubber band gets colder on stretching. Jun 05, 2017 entropy change stretching and contracting at constant t. 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. 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.
Bertrand, professor of chemistry thermodynamics in two dimensions surface tension. 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. Thermodynamics of a rubber band, american journal of physics 31 5. 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. To measure partial derivatives experimentally and test the validity of the cyclic rule of partial differentiation. Watch your teachers demonstration and answer the following. So he observed that stretched rubber contracted on heating and elongated. This should imply the entropy of the rubber band has decreased, but how does the entropy of the whole universe increase here. In the following you will calculate the temperature and entropy change of stretching and. Rubber as an aid to teach thermodynamics indian academy of.
Pdv work must be done on the rubber band to stretch it, and. Place the rubber band flat on a table and mark two lines from where the rubber bands elasticity will be measured. Dwrev3d pdv, and occasionally with work in onedimension. The flory theory of rubber elasticity has pointed out the rubber elasticity has primarily entropic origins. Second, and third laws of thermodynamics, energy minimization and entropy maximization, fundamental equations, intensive vs. Rubbers thermodynamic phenomenology is also often counterintuitive. Release the tension on the rubber band and touch it to their upper lip, the rubber band will feel cooler. A refrigerator that works by stretching rubber bands youtube. 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.
Pdf exploring the thermodynamics of a rubber band researchgate. Then quickly release the tension and press the rubber band against your lips. Umr chemlabs thermodynamics of rubber elasticity pch 599 gary l. Rubber bands provide an appealing subject for a ther. Another surprising phenomenon is that a rapidly stretched rubber band will. Since the stretching of the rubber band was an adiabatic change, there. H is negative for stretching the rubber band and positive when the rubber band contracts. Roussel department of chemistry and biochemistry university of lethbridge february 21, 2009 a rubber is a material that can undergo large deformations e. The calculation involves the probability of finding the system with a given distribution of molecular configurations. Exploring the thermodynamics of a rubber band david roundy department of physics, oregon state university, corvallis, oregon 97331. Next, observe the ml beaker and convert the distance the rubber band could stretch from ml to cm. When i stretch a rubber band, the fibers straighten out causing lesser randomness and more order. I have the students pick up a rubber band as they come into the room. Thermodynamics demonstration originally prepared for the coursera mooc.
Students stretch precut rubber bands to their lips, stretch the rubber bands, and then allow them to contract. An elastomer has rather unusual physical properties. 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. Following this a discussion of the applicability and the. C differential but it is a differential made by rubber band thermodynamics. 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. Using the same effect, a stretched rubber band will contract on its own when heated. In rubber the elastic force is due to the thermal interactions of the molecules within the material.
By heating the rubber band, we increase the entropy. On stretching a rubberband does the entropy increase or decrease. 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. My text says that on stretching, the arrangement of particles become m. The odd behavior of rubber bands thomas stoebe university of washington seattle, wa. Statistical thermodynamics of rubber rubber chemistry. Rubber band thermodynamics a refrigerator powered by. The key lies in the reason for the stretchiness of the rubber band. In order to feel the heat from the rubber band the student needs to physically stretch the rubber band. Thermodynamics of rubber bands recommended for chapters. 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.
A rubber band also known as an elastic band, gum band or lacky band is a loop of rubber, usually ring shaped, and commonly used to hold multiple objects together. The rubber band was patented in england on march 17, 1845 by stephen perry. Exploring the thermodynamics of a rubber band oregon state. The entropy change for the stretching of rubber is calculated by statistical methods, neglecting intermolecular attractions and deformation of bonds and bond angles.
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. 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. Thermodynamics and equilibrium 145 here is a simple experiment. Then measure the length of the rubber band within the marks just drawn. Extensive variables 1 the following equations of state each violate at least one basic principle of. A thermodynamic analysis of these two experiments can tell us something about the molecular structure of rubber. As the middle of the string moves, the ends of the. Following this a discussion of the applicability and the limitations of the theory is presented. The odd behavior of rubber bands materials science and. Fys2160, thermodynamics and statistical physics, fall 2019 due. Rubber band thermodynamics a refrigerator powered by stretching rubber bands ok so its only a 2. Consider a rubber band under tension, f, with length per.