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# Laporan unit 2

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### Laporan unit 2

1. 1. FRICTION FORCE Nurul Qalbi Fadilah 1, Nurfajrina Mutmainnah 2, Muh Nurul Kamal Purnama 3, A.Sriatu Nurdianti Departement of Chemistry, FMIPA State University of Makassar 2013 Abstract. Have done experiment about friction force. The Purpose of experiment to (1) understand the factors that influenced friction force, (2) understand concept of static and kinetic friction, and (3) determine the coefficient of static and kinetic friction. Data obtained by using tools spring balance,table pulley,rough beam,smooth beam,rope/yarn,load,foundation board,incline plan,square beam,stopwatch,meter. First activity,observed attraction force of state object.second activity,find the relationship between normal force to friction force.third activity, find relationship between state of surface friction.fourth activity,determine coefficient of static friction on incline. Fifth activity, determine coefficient of kinetic friction inclined plane.Collect data on activities first to third activities that looked basically same tensile force on object is at montionless, ready to move and regular rectilinear motion only on activities that differentiate beams 1 and 3 used same mass but also activities 3 use two different types of surfaces, activities 2 use same type of surface and different normal force. While, activity 4 determine critical angle of objects with different gravity, activitiy 5 determine travel time by different mileage. So,conclusion of this practicum is frictional force is affected by normal force, coefficient of friction, critical angle, and type of surface. KEYWORDS: Friction force, static friction force, kinetic friction force, normal force, coefficient static friction,coefficient kinetic friction, condition object : montionless, ready to move, regular rectilinear motion. PREFACE Did you ever ride a bike ? If you have not , try it . What do you feel when riding a bike ? Why bike can move ? Is a moving bicycle can be stopped ? How do you stop it ? Encouragement , stroke , kick , pull , or other things that cause objects to move or stop the movement of the so-called style . In physics , force is defined as an impulse or a pull . If we pay attention to the movements of objects , such as speeding and stopping the bike , changing the direction of the ball for a kick , and the enlargement of the surface of the inflated balloon , it can be concluded that the force exerted on an object can cause changes in the body according to the force applied. If you pay attention to these forces, whether the source object given the force and force is always in contact? Yes, some styles can occur without a touch of force between the source and the object is given the force. This is the nature of the underlying force grouping into a force touch and don’t touch force. Touch force is a force act on an object with point on the surface of the object. friction force including tap force that appears if the surface of the two objects come into contact physically. Toward the direction of the friction surface and the touch area with a tendency toward motion whether it is motionless, ready to move, or regular rectilinear motion. If we look the statement above , there is a question why the frictional force influenced the state of objects at montionless, ready to move, and regular rectilinear motion? So the answer of these questions are at that time, the object who is montionless there’s no frictional force because the force that occurs of the object is very small objects then when the thing would be regular, the object will undergo static frictional force because the force that occurs on the object is large enough that the object is regular or the force act on an object is equal to the frictional force occurs, and when the object regular rectilinear, motion object has kinetic frictional force because the force that applied is greater than frictional force that occurs so that the object is regular rectilinear motion.
2. 2. Then the next question is what is the formula to determine the static and kinetic coefficient of friction? The answer to the question which is to determine the formula of the static friction coefficient using the formula (1) and to determine the formula of the kinetic friction coefficient using the formula (2). The classic rules of sliding friction were discovered by Leonardo da Vinci (14521519), but remained unpublished in his notebooks. They were rediscovered by Guillaume Amontons (1699). Amontons presented the nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together. This view was further elaborated by Belidor (representation of rough surfaces with spherical asperities, 1737) and Leonhard Euler (1750), who derived the angle of repose of a weight on an inclined plane and first distinguished between static and kinetic friction. A different explanation was provided by Desaguliers (1725), who Demonstrated strong cohesion forces between the spheres of roomates lead a small cap is cut off and roomates were then brought into contact with each other. The understanding of friction was further developed by Charles-Augustin de Coulomb (1785). Coulomb Investigated the influence of four factors on friction play: the nature of the materials in contact and their surface coatings; the extent of the surface area; the normal pressure (or load), and the length of time that the surfaces remained in contact ( time of repose). Coulomb Considered further the influence of sliding velocity, temperature and humidity, in order to decide between the different Explanations on the nature of the friction that had been proposed. The distinction between static and dynamic friction is made in Coulomb's friction law (see below), although this distinction was already drawn by Johann Andreas von Segner in 1758. The effect of the time of repose was explained by Musschenbroek (1762) by considering the surfaces of fibrous materials, with fibers meshing together, roomates takes a finite time in the friction increases roomates. John Leslie (1766-1832) Noted a weakness in the views of Amontons and Coulomb. If friction arises from a weight being drawn up the inclined plane of successive asperities, then why is not it balanced through descending the opposite slope? Equally Leslie was skeptical about the role of adhesion proposed by Desaguliers, roomates should on the whole have the same tendency to Accelerate as to retard the motion. In his view friction should be seen as a time-dependent process of flattening, pressing down asperities, roomates creates new obstacles in what were cavities before. Arthur Morrin (1833) developed the concept of sliding versus rolling friction. Osborne Reynolds (1866) derived the equation of viscous flow. This completed the classic empirical models of friction (static, kinetic, and fluid) commonly used today in engineering. The focus of research during the last century has been to understand the physical Mechanisms behind friction. F. Phillip Bowden and David Tabor (1950) Showed that at a microscopic level, the actual area of contact between surfaces is a very small fraction of the apparent area. This actual area of contact, by the caused by " asperities "(roughness) increases with pressure, explaining the proportionality between normal force and frictional force. The development of the atomic force microscope (1986) has recently enabled Scientists to study friction at the atomic scale[1].
3. 3. At the time this trial is the friction experiments. The purpose of the implementation of this experiment was to determine the factors that affect the friction force, understand the concept of static and kinetic friction and determine the static and kinetic coefficient of friction. In the practicum, there are five methods of frictional force performed. Who first observed the tensile force of the state of the object by using the same beam mass to determine the tensile force on the object when the object was montionless, ready to move, and regular rectilinear motion. Second looked at the relationship between the normal force to the friction force is the same surface normal but different force to determine tensile force on the object is at montionless, ready to move and regular rectilinear motion.Similarly, the second practicum, the practicum looked at the relationship between the state of the three surfaces with a friction force observed gravity objects at rest, ready to regular, and regular rectilinear motion but the type of surface used the refined and coarse surfaces. In the fourth practicum, determine the coefficient of static friction on an inclined plane to calculate the critical angle of objects to determine in advance determine the gravity of objects. And on the fifth practicum, which determine the coefficient of kinetic friction on an inclined plane by first determining the distance that must be traversed by the beam / objects to calculate the travel time required to get to the end object of the incline with a stopwatch. THEORY Friction force is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Friction force includes a stylish touch , which appears when two surfaces come into contact physical objects . Direction of the force of friction with the surface of the touch pad in the direction opposite to the trend and direction of motion. Friction is the force directed against the motion or tendency toward the object will move. Friction occurs when two objects come into contact. The objects in question here does not have to be solid, but can also be a liquid, or gas. Friction between two solid objects such is the static and kinetic friction, while the force between solids and liquids and gases is the Stokes force. Picture 1. Frictional force (Ff) of a moving object over a surface board There are two types of friction between two solid objects moving straight to each other, the force of static friction and kinetic friction, which distinguished between the touch points between the two surfaces is fixed or mutual change (shift). Static friction is friction
4. 4. between two solid objects that are not moving relative to each other. Coefficient of static friction is generally denoted byμs, and are generally larger than the coefficient of kinetic friction. Static friction force generated from a force that is applied just before the object is moving. The maximum frictional force between two surfaces before movement is the result of the static friction coefficient multiplied by the normal force. When no movement occurs, the frictional force can have a value of zero to the maximum frictional force. Each style is smaller than the maximum frictional forces trying to move one of the objects will be resisted by the friction force equal to the force is large, but in the opposite direction. Every style that is greater than the maximum frictional force will cause the movement occurs.Once movement occurs , static friction force can no longer be used to describe the kinetics of objects, making use of kinetic friction. Kinetic friction ( or dynamic ) occurs when two objects move relative to each other and rub against each other. Coefficient of kinetic friction is generally denoted by μk and are generally always smaller than the static friction for the same materials Friction is the accumulation of micro interactions between the two surfaces that are touching each other. Styles that work include the electrostatic forces on each surface. First believed that the smooth surface will cause friction (or rather the friction coefficient) becomes smaller value compared with a rough surface, but today is no longer the case. Construction of micro (nano to be exact) on the surface of an object can cause friction to a minimum, even liquids can no longer to be wet In general, the friction force can be written as a series expansion, such as : , f the friction force direction opposite to the force F causes , and apply : 1. For the price o F <fsthen beam itmontionless. 2. For the price F = fsthen the beamprecise to move. 3. If phase enlarged so that F >fsthe moving objects and static friction forcefswill turn into kinetic frictional forcefk. Friction force between two surfaces mutually silent one against the other so-called static friction . The maximum static friction force is equal to the smallest force needed to begin moving object . Once motion has begun , the friction force between two surfaces is usually reduced so a smaller force is needed to keep things moving irregularly . Force acting between the two surfaces move relative to each other is called kinetic friction . If the big statesfsthe maximum force of static friction , then : s fs N (1.1) With s is the coefficient of static friction and the normal force N is large . If the big states fkkinetic frictional force , then :
5. 5. fk N k with k (1.2) iscoefficient of kinetic friction. When an object is at rest on a flat surface , and then place the object plane is tilted slowly to an angle right to object to the move, the coefficient of static friction between the object and the field is given by the equation , S = tan (1.3) c With cis the angle at the right things will move , called the critical angle . Coefficient of static friction is the tangent value of the angle of the field , with the appropriate state object will move / slide . At angles greater than c , uniformly accelerated beam sliding into the lower end of the inclined plane with acceleration: ax g (sin k cos ) (1.4) where is the angle of the field and k is the coefficient of kinetic friction between the object plane.By measuring the acceleration ax, so coefficient of friction kcan be measured. EXPERIMENTAL METHODOLOGY Before do practicum of friction force ,we need prepare necessary equipment and material in the practicum. The equipment and material are 0-5 N spring balance, pulley table, the beam has two surfaces with a surface that is coarse and refined surfaces, weight 50 grams and 100 grams, string / yarn, board basis, inclined plane, which has a square beam with connective stecker, stopwacth, and gauges as well as writing equipment. the variables identified in this practicum. At first activities practicum observing tensile force of the state of objects, while the variable object manipulation is object then the variable response of these activities and the tensile force control variable is the mass of the beam. Operational definition of variables 1 praktium activities that manipulation of state variables of objects that always be changed from a state of montionless, precise to move and uniform line motion impact on the response variable gravities constant changes of 0.5, 1.6 and 1 , 2 and the control variables are fixed with the beam of mass 1.9 N.In the practicum activities 2 which looked at the relationship between the normal force with friction , variable object manipulation is the normal force and the state of objects then this activity is the response variable tensile force objects and variables that control the type of surface used . Operational definition of the variable activity 2 state manipulation of objects at montionless then precise to move and uniform line motiom , normal force object further changed by adding to the burden on the body with a load of 50 grams , 100 grams and 150 grams so the normal force of the object different , ie the manipulated variable gravity objects will change but , tensile force on the object stationary object remains the same object then a tensile force on the state of precise to move and uniform line motion has increased every change of the normal force of the object , and the control variables type of surface used is slippery surfaces.In the practicum activities 3 that looked at the relationship between the state of the surface friction conditions, variable manipulation is a type of surface and the state of objects, the response variable tensile force objects and variable control of this activity is the normal force object. Operational definition of the variable activity 3 the manipulation variable surface types interchangeable with each measurement done with 2 types of surface used is a coarse surface and refined surface and the state of the object at montionless precise to move then and