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Unformatted text preview: Physics 6B Stress, Strain and Elastic Deformations Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB When a force is applied to an object, it will deform. If it snaps back to its original shape when the force is removed, then the deformation was ELASTIC. We already know about springs  remember Hooke’s Law : F spring = k•Δx Hooke’s Law is a special case of a more general rule involving stress and strain. .) const ( Strain Stress = The constant will depend on the material that the object is made from, and it is called an ELASTIC MODULUS. In the case of tension (stretching) or compression we will call it Young’s Modulus*. So our basic formula will be: Strain Stress Y = *Bonus Question – who is this formula named for? Click here for the answer Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB To use our formula we need to define what we mean by Stress and Strain. STRESS is the same idea as PRESSURE. In fact it is the same formula: Area Force Stress = Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB To use our formula we need to define what we mean by Stress and Strain. STRESS is the same idea as PRESSURE. In fact it is the same formula: Area Force Stress = STRAIN is a measure of how much the object deforms. We divide the change in the length by the original length to get strain: L L Strain ∆ = Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB To use our formula we need to define what we mean by Stress and Strain. STRESS is the same idea as PRESSURE. In fact it is the same formula: Area Force Stress = STRAIN is a measure of how much the object deforms. We divide the change in the length by the original length to get strain: L L Strain ∆ = Now we can put these together to get our formula for the Young’s Modulus: L L A F Y ∆ = Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Problem 11.6 A nylon rope used by mountaineers elongates 1.10m under the weight of a 65.0kg climber. If the rope is initially 45.0m in length and 7.0mm in diameter, what is Young’s modulus for this nylon? Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB ΔL=1.1m L =45m Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Problem 11.6 A nylon rope used by mountaineers elongates 1.10m under the weight of a 65.0kg climber. If the rope is initially 45.0m in length and 7.0mm in diameter, what is Young’s modulus for this nylon? ΔL=1.1m L =45m A couple of quick calculations and we can just plug in to our formula: L L A F Y ∆ = Prepared by Vince Zaccone For Campus Learning Assistance Services at UCSB Problem 11.6 A nylon rope used by mountaineers elongates 1.10m under the weight of A nylon rope used by mountaineers elongates 1....
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 Spring '11
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 Physics, Force, Vince Zaccone, Campus Learning

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