A Study On Hookes Law Mechanics Essay

A Study On Hookes Law Mechanics studyHOOKES LAW Hookes policeof conciliatoryity is an approximation that states that the extension of a source is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. Materials for which Hookes law is a useful approximation are known as linear elasticor Hookean fabrics.If a alloy is lightly continueinged, a fleeting deformation permitted by an elastic displacement of atoms in space takes place. Removal of evince results in a gradual return of metal to its original shape. Mathematically, Hookes law states thatWhere,xis the displacement of the end of the resound from its equilibrium positionFis the restoring depict exerted by the material andkis theforce constant(orspring constant).DIAGRAMATICALLY-When no weight is applied to the spring, the edition is zero,And, we can measure its length,. and when we drill a force F to the spring It stretches And it extends length,x, that is, the figure, c aused by the attempt isF = mg.Also,In terms of mechanics hooks state that-For an elastic material stress applied on a body is directly proportionate to the strain producedThat is, eOr = E e Where, is the stress appliede is the strain developedE is the YOUNGS MODULUS OF ELASTICITYNowSTRESS it is the force causing the deformation.It is measured in unit of measurements of force per unit area of cross-section (N.m-2) denoted by(sigma).That is = F/AUnits of stress are PascalStrain is the deformation that takes place in the body.It is the ratio of the increase in length,DLto the original length (L), Represented by symbol(epsilon) or e.That is e=DL/LIt is dimensionless.And according to hooks law = E eOr, E = /ePutting values of stress and strain in above equation we get-E = F-L/A-DLYoungs modulus of elasticity (E) is defined as the ratio of unit stress to unit strain .GENERALIZED HOOKS LAWThe generalized Hookes Law can be used to predict the deformations caused in a given material by an arbitrary combination of stresses.The linear relationship between stress and strain applies forThe generalized Hookes Law also reveals that strain can exist without stress. For example, if the member is experiencing a load in the y-direction (which in turn causes a stress in the y-direction), the Hookes Law shows that strain in the x-direction does not equal to zero. This is because as material is being pulled outward by the y-plane, the material in the x-plane moves inward to fill in the space once occupied, just like an elastic band becomes thinner as you try to pull it apart. In this situation, the x-plane does not have any external force acting on them but they experience a change in length. Therefore, it is valid to say that strain exist without stress in the x-plane.STRESS-STRAIN CURVE-Thestress-straincurve is a graphical representation of the relationship betweenstress, derived from measuring the load applied on the sample, andstrain, derived from measuring thedeforma tionof the sample, i.e. elongation, compression, or distortion. The nature of the curve varies from material to material.ELASTIC LIMITThe elastic limit is where the graph departs from a straight line. If we go past it, the spring wont go back to its original length. When we remove the force, were left with apermanent extension.Below the elastic limit, we say that the spring is showing elastic behaviour the extension is proportionate to the force, and itll go back to its original length when we remove the force.Beyond the elastic limit, we say that it shows plastic behaviour. This means that when a force is applied to deform the shape, it be deformed when the force is removed.YIELD POINTTheyield strengthoryield pointof a materialis defined in engineering and material science as the stress at which a material begins to deform plastically . Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. at one t ime the yield point is passed some fraction of the deformation will be permanent and non-reversible.True elastic limitThe lowest stress at whichdislocationsmove. This definition is rarely used, since dislocations move at very low stresses, and detecting such movement is very difficult.Proportionality limitUp to this amount of stress, stress is proportional to strain hookes law so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.Elastic limit (yield strength)Beyond the elastic limit, permanent deformation will occur. The lowest stress at which permanent deformation can be measured. This requires a manual load-unload procedure, and the accuracy is critically qualified on equipment and operator skill. For elastomers such as rubber the elastic limit is practically larger than the proportionality limit. Also, precise strain measurements have shown that plastic strain begins at low stresses. Offset yield point (proof stres s)This is the most widely used strength measure of metals, and is found from the stress-strain curve. A plastic strain of 0.2% is ordinarily used to define the offset yield stress, although other values may be used depending on the material and the application. The offset value is given as a subscript, e.g., Rp0.2=310 MPa. In some materials there is essentially no linear region and so a certain value of strain is defined instead. Although around arbitrary, this method does allow for a consistent comparison of materials.Upper yield point and lower yield pointSome metals, such as tame steel reach an upper yield point before dropping rapidly to a lower yield point. The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the upper yield point, and beyond rubber band can develop.NUMERICALS-Q1) When a 13.2-kg mass is placed on top of a upended spring, the spring compresses 5.93 cm. Find the force constant of the spring.Solution Mass = 13.2 kgWeight = 13.2-9.8= 129 Compression (x) = 5.93 = 0.0593 m From Hookes Law F = kxThe force on the spring is the weight of the object, i.e.(F) = 129 NPutting values of force and compression in above equation129 = (0.0593) - kOr,k = 2181 N/m AnswerQ2) A 3340 N ball is supported vertically by a 2m diameter steel cable assuming cable has a length of 10m, determine stress and strain in the cable. Youngs modulus for steel is 200N/sq.m.Solution Force (F) = 3340NDiameter = 2mRadius (r) = 1mLength of cable = 10mYoungs modulus (E) = 200N/sq.mNow we know,Stress () = F/AArea = = 3.14-1-1 = 3.14So, = 3340/3.14 = 1063.69N/m.sqAlso, strain (e) = /EPutting valuese = 1063.69/200e =5.3184Answer Q3) If a spring has a spring constant of 400 N/m, how much work is required to compress the spring 25.0 m from its undisturbed position?Solution spring constant (K) = 400 N/mcompression (x) = 25m we know, force required for compres sion- F = kx i.e. F = 40025 = myriadNand work done = force x compressionw = F x Xw = 10000 x 25w = 25,000 Joules AnswerQ4) On a of steel rod of length 15m and diameter 6m a force of 60N is applied. Calculate the extension and bare-ass length of the rod. Youngs modulus of steel is 250N/m.sq.Solution Force (F) = 60 NDiameter = 6mSo, Radius (r) = 3m Length (L) = 15 mYoungs modulus (E) = 250N/m.sq.Now,Area (A) A = 3.14 x 3 x 3A = 28.26 sq.mAlso, , E = F-L/A-DLOr, DL = F-L/A-EDL = 60-15/28.26-250 DL = 0.127mSO, new length = 15+0.127L = 15.127m ANSWERREFERENCES-1) www.physicsworld.com2) www.wikipedia.org3) www.123iitjee.com4) www.physicsforum.com5) www.matter.org.content/HookesLaw6) www.webphysics.davidson.edu/hook7) www.scienceworld.com