Hysteresis

Hysteresis is a phenomenon in physics whereby changes in physical properties of objects lag behind alterations in the forces that allow those properties to exist. Scientists exemplify hysteresis most often in relation to magnetism. The phenomenon can be observed when a magnetized object remains magnetized even after the magnetic force is removed. Opposite magnetic force must sometimes be applied to the object to eliminate its magnetization. The hysteresis in this case indicates the presence of a kind of magnetic memory in the object. Hysteresis can occur in any system containing objects to which forces are applied. The forces are called input. The objects' corresponding reactions to the forces are called output. In addition to the field of magnetics, hysteresis can occur in a variety of other areas, such as biology, mechanics, and economics.

Background

The word hysteresis derives from Greek and means "a coming short" or "a deficiency." Scientists explain hysteresis most often in the context of magnets. This is because the application of magnetic forces to objects creates ideal systems for hysteresis to occur. Certain basic conditions must always be met for hysteresis to take place in magnetic contexts. To be affected by magnetic force at all, an object must be ferromagnetic. Ferromagnetism is the ability of a material to magnetize, or to react strongly to magnetic forces. Ferromagnetism depends on an object's temperature, chemical composition, crystalline structure, and subatomic particle arrangement. Metals and metal alloys, or mixtures of different metals, are the most well-known ferromagnetic materials. Metals such as iron and nickel react particularly readily to magnetic forces.

Magnetism exists because of the electrical charges of the particles that compose atoms, the smallest units of matter. These charges create magnetic fields that allow objects to react to magnetic forces. Particles called electrons, which exude negative electrical charges, create most of the magnetic fields for an object. All electrons create magnetic fields naturally by moving. Scientists do not know for certain why this happens.

All atoms' electrons create magnetic fields, but not all matter reacts to magnetic force. This is because the fields of many objects' electrons are chaotically arranged and point in all directions. Magnetic fields that cross paths are canceled out. Magnetic fields that travel in the same direction, however, create net magnetic fields, or those that allow objects to react to magnetic forces. Objects that do not react to magnetism, such as human beings and plants, feature electrons with chaotic magnetic fields; people would be able to stick to other objects with magnetic force if their electrons produced directionally aligned magnetic fields. The electrons of highly magnetic objects such as metals create organized magnetic fields.

Overview

Hysteresis occurs in both natural and created systems. Natural systems are simply processes that occur in nature. Created systems are made by humans and include machines, businesses, and political processes. Incidents of hysteresis are measured on input-output graphs. The graphs plot points across their planes to measure how objects or characteristics of those objects change as certain forces are applied to them. In the context of hysteresis, input-output graphs usually measure how ferromagnetic objects react to magnetic force. The physical points and lines plotted on the graphs help scientists see exactly what happens when hysteresis occurs.

For example, a ferromagnetic object that has been magnetized with a powerful magnetic force can be charted on an input-output graph, with the force being the input and the magnetization of the object being the output. Input-output graphs are standard four-planed graphs. Lines are used to show how a ferromagnetic object's magnetic field increases as the magnetic force applied to it increases. The line representing this rises from the intersection of the x and y axis through the upper right quadrant, or square, of the graph. Hysteresis is represented by a second line that descends the graph after the magnetizing force has been removed. The hysteresis line does not follow the trajectory of the original line. Instead, it takes a longer, more indirect arc back to the point of zero magnetization, even though the magnetizing force has been removed. The point at which the object continues displaying magnetization despite the absence of the magnetizing force is known as the point of retentivity. It shows that the object has retained some residual magnetism, or kept a memory of its fully magnetized state. This phenomenon is hysteresis.

Hysteresis can also occur in other kinds of systems, such as biology. Human tissues, for instance, can experience hysteresis through physical therapy. The repetitive training of ligaments to bear large amounts of weight will, over time, allow the ligaments to grow and therefore be able to bear that same weight even after the therapy has ended. Hysteresis, therefore, can help people rehabilitate their bodies following an injury or simply to strengthen their ligaments and muscles through exercise.

Economics is another system that supports hysteresis, although in different, nonphysical ways. Economic hysteresis generally appears when an economy experiences ripple effects over time from a single disturbance in normal economic activity. An example is widespread unemployment that gradually damages a national economy. The disturbance is the country's unemployment rate reaching a certain level.

Over time, more people become accustomed to the lower standards of living associated with being unemployed. They simultaneously become less motivated to escape their situations by finding work. As a result, unemployment becomes socially acceptable. This large-scale unemployment harms the overall national economy. Even when the job market recovers, these people may still not be interested in finding work. All this economic damage resulted from one depressed period in a nation's economy. The lag in the disturbance's effects is hysteresis.

Bibliography

Bertotti, Giorgio. Hysteresis in Magnetism: For Physicists, Materials Scientists, and Engineers. Academic Press, 1998, 31–33.

Fox, Stuart. "How Do Magnets Work?" Live Science, 8 June 2010, www.livescience.com/32633-how-do-magnets-work.html. Accessed 27 June 2017.

"Hysteresis." Investopedia, www.investopedia.com/terms/h/hysteresis.asp. Accessed 27 June 2017.

"The Hysteresis Loop and Magnetic Properties." NDT Resource Center, www.nde-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.html. Accessed 27 June 2017.

James, Richard D. "Figure 1: Typical Hysteresis Loops in Hard, Soft and Autarkic Magnets." Nature, 21 May 2015, www.nature.com/nature/journal/v521/n7552/fig‗tab/521298a‗F1.html. Accessed 27 June 2017.

Meyer, Don. "Ligament Hysteresis, Creep, Recovery and Plastic Deformation." American Journal of Clinical Chiropractic, 11 Sept. 2011, www.chiropractic-biophysics.com/clinical‗chiropractic/2011/9/12/ligament-hysteresis-creep-recovery-and-plastic-deformation.html. Accessed 27 June 2017.

Morris, K.A. "What Is Hysteresis?" University of Waterloo, www.math.uwaterloo.ca/~kmorris/Preprints/Morris‗hysteresis‗final.pdf. Accessed 27 June 2017.

Parks, Natasha. "List of Ferromagnetic Metals." Sciencing, sciencing.com/list-ferromagnetic-metals-8479101.html. Accessed 27 June 2017.