Friction Lab Essay

Discussion and ReviewWhenever a body slides along an different(prenominal) body a resisting describe is called into play that is kn receive as clangoring. This is a very important take in and serves many useful purposes. A soulfulness could not walk without detrition, nor could a car propel itself along a highway without the clash amid the tires and the road rise. On the other hand, clang is very wasteful. It subjugates the efficiency of machines because work must be done to master it and this energy is wasted as instigate. The purpose of this experiment is to study the laws of clash and to determine the coefficient of clangour between 2 surfaces. THEORYFriction is the resisting personnel department encountered when one surface slides over another. This kurrat acts along the tangent to the surfaces in contact. The force necessary to overcome crash depends on the nature of the materials in contact, on their roughness or smoothness, and on the mean(a) force neverth eless not on the area of contact or on the animate of the motion. We find experimentally that the force of friction is directly proportional to the ruler force. When an object is sitting on a horizontal surface the normal force is just the freight of the object. However, if the object is on an incline then(prenominal) it is not agree to the weight but is fancyd by N= mg cos . The constant of proportionality is called the coefficient of friction, . When the contacting surfaces are actually skid one over the other the force of friction is given byEquation 1Ffr = k FNwhere Ffr is the force of friction and is directed line of latitude to the surfaces and opposite to the direction of motion. FN is the normal force and k is the coefficient of kinetic friction. The substandard k stands for kinetic, meaning that k is the coefficient that applies when the surfaces are movingone with keep an eye on to the other. k is therefore more precisely called the coefficient of kinetic or slide friction. Note carefully that Ffris everlastingly directed opposite to the direction of motion. This federal agency that if you reverse the direction of sliding, the frictional force reverses too. In short, friction is always against you. Friction is called a non-conservative force because energy must be employ to overcome it no matter which way you go. This is in contrast to what is called a conservative force such as gravity, which is against you on the way up but with you on the way blast.Thus, the energy expended in lifting an object may be regained when the object descends. Yet, the energy used to overcome friction is dissipated, which mode it is lost or made unavailable as heat. As you depart see in your later study ofphysics the distinction between conservative and non-conservative forces is a very important one that is fundamental to our concepts of heat and energy.A method of checking the proportionality of Ffr, and FNand of determining the proportionality constant k is to have one of the surfaces in the form of a matted rigid horizontally with a pulley fastened at one end. The other surface is the bottom face of a distract that rests on the unwavering and to which is attached a weighted cord that passes over the pulley. The weights are vary until the trap moves at constant speed after having been causeed with a dismiss push. Since there is no acceleration, the net force on the block is zero, which mean that the frictional force is adjoin to the tension in the cord.This tension, in turn, is equal to the total weight attached to the cords end. The normal force between the two surfaces is equal to the weight of the block and faecal matter be increased by placing weights on top of the block. Thus, corresponding look upons of Ffr,and FN can be found, and plotting them entrust show whether Ffrand FN are indeed proportional. The slope of this interpret gives k. When a body lies at rest on a surface and an attempt is made to push it, th e pushing force is opposed by a frictional force. As long as the pushing force is not strong enough to start the body moving, the body be in proportionality.This means that the frictional force automatically adjusts itself to be equal to the pushing force and thus to just be enough to equaliser it. However, there is a threshold economic value of the pushing force beyond which larger values willing cause the body to break onward and slide. Weconclude that in the unchanging case where a body is at rest the frictional force automatically adjusts itself to keep the body at rest up to a certain level best. just now if static equilibrium demands a frictional force larger than this maximum, static equilibrium conditions will cease to exist because this force is not available and the body will start to move. This situation may be expressed in equation form asEquation 2Ffr sFN or Ffr max = sFNWhere Ffris the frictional force in the static case, Ffr max is the maximum value this for ce can assume and sis the coefficient of static friction. We find that sis some larger than k. This means that a somewhat larger force is unavoidable to break a body outside and start it sliding than is required to keep it sliding at constant speed once it is in motion. This is why a s lessen push is necessary to get the block started for the measurement of k. whizz way of investigating the case of static friction is to observe the so-called limiting weight down of repose. This is defined as the maximum angle to which an inclined plane may be tipped onwards a block placed on the plane just starts to slide. The sight is illustrated in Figure 1 above. The block has weight W whose grammatical constituent Wcos (where is the plane angle) is perpendicular to the plane and is thus equal to the normal force, FN. The voice Wsin is parallel to the plane and constitutes the force urging the block to slide follow out the plane. It is opposed by the frictional force Ffr, As long as the block remains at rest, Ffr must be equal to W sin . If the plane is tipped up until at some value max the block just starts to slide, we haveEquation 3ButHenceOrThus, if the plane is gradually tipped up until the block just breaks away and the plane angle is then measured, the coefficient of static friction is equal to the tangent of this angle, which is called the limiting angle of repose. It is interesting to note that W cancelled out in the derivation of Equation 3 so that the weight of the block doesnt matter.PROCEDUREThis experiment requires you to record measurements in Newtons. Remember that in SI units the unit of force is called the Newton (N). One Newton is the force required to impart an acceleration of 1m/s2 to a muckle of 1 kg. Thus 1 N = 1 kg.m/s2. You can substitute any kg- potentiometer to Newtons by multiplying the kg-weight by 9.8 m/s2, i.e., 100 g = 0.1 kg = 0.1 x 9.8 = .98 N. 1.Determining force of kinetic or sliding friction and static friction a. The wooden b locks provided in the LabPaq are too light to give good readings so you need to put some weight onthem, such as a full soft alcohol addiction can. Weigh the plain wood block and the object used on top of the block. Record the combined weight in grams and Newtons.b. Place the ramp board you provided horizontally on a table. If necessary tape it down at the ends with masking tape to keep if from sliding.c. Begin the experiment by setting the block and its weight on the board with its largest surface in contact with the surface of the board. Connect the blocks hook to the 500-g imprint outdo. d. Using the spring scale, late pull the block lengthwise along the horizontal board. When the block is moving with constant speed, note the force indicated on the scale and record. This is the approximate kinetic or sliding frictional force. arrogate two more times.e. While carefully watching the spring scale, start the block from rest. When the block just starts to move, note the force indi cated on the scale and record. You should notice that this requires more force. This force isapproximately equal to the static frictional force. Repeat two more times.Determining coefficient of static friction using an inclined surfacea. Place the plain block with its largest surface in contact on the board while the board is lying flat.b. tardily raise one end of the board until the block just breaks away and starts to slide down. Be very careful to movethe plane slowly and smoothly so as to get a precise value of the angle withthe horizontal at which the block just breaks away. This is the limiting angle of repose max. Measure it with a protractor (see photo that follows for an alternate way of amount the angle) and record the result. You may also want to measure the base and the tip of the triangle formed by the board, the support, and the floor or table. The height divide by the length of the base equals the coefficient of static friction.Rememberc. Perform two more trials . These trials should be independent. This means that in each case the plane should bereturned to the horizontal, the block placed on it, and the plane carefully locomote up until the limiting angle of repose is reached.DATA TABLE 6HeightBase Length maxsTrial 1Trial 2Trial 3AverageCalculations1. Using the intensity of the block and the average force of kinetic friction from Data hold over 1, calculate the coefficient of kinetic friction from Equation 12. Using the mass of the block and the average force of kinetic friction from Data fudge 2, calculate the coefficient of kinetic friction for the woodblock sliding on its side. Record your result and see how it compares with the value of kobtained from Data Table 1.3. From the data in Data Table 3, 4 & 5 compute the coefficient of static friction, sfor, the glass surface on wood, the sandpapered surface on wood, and wood on carpet, etc from each of your three trials. Calculate an average value of s.Record your results in your own data sheets.4.From the data obtained in Data Table 6 calculate sfor wood on wood from each of your three trials.5.Calculate an average value of s. Record your result on the data sheet.QuestionsA. How does the coefficient of static friction compare with the coefficient of kinetic friction for the same surfaces and areas?B. Why is it important to reduce friction during the operation of machinery? C. How does grease or oil affect the coefficient of friction?