20171108

Online reading assignment: elasticity

Physics 205A, fall semester 2017
Cuesta College, San Luis Obispo, CA

Students have a bi-weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing a presentation on elasticity.


Selected/edited responses are given below.

Describe what you understand from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically demonstrate your level of understanding.
"Strain, tension and Young's modulus and what they represent. Tension is stretching something out while compression is bringing stuff together."

"Tension is a pulling force, with tension stress being a pulling force applied to a material, while tension strain is how the material reacts. Compression is a squishing force, similarly with compressive stress peing a pressing force to a material and compressive strain being how the material reacts."

"Elasticity is the nondestructive stretching or squishing. The tension in stretching, compression is squishing."

"Elasticity is a material's ability to cope with stress/strain or tension/compression. These variables are balanced in Hooke's law, where the energy from stress is equal to the material's strain and its Young modulus."

"Force applied along the x axis is equal to x displacement times a proportionality constant k. Pressure is expressed as P equal to force F on a perpendicular surface divided by area A."

"The use of tensile stress and compression stress seem pretty simple. Tensile is applying a force to 'stretch' something and compression is applying a force to 'squish' something."

"A material is considered elastic when it can be bowed (whether squished or stretched), but returns to its original state after. Tension is when such material is stretched whereas compression is when it is squished. There are two types of stress and strain: tensile and compressive. Tensile stress is when you apply force to a cross-section sample to stretch it, but tensile strain is how the material responds. Compressive stress is when you apply force to a cross-section sample to squish it, but compressive strain is how the material responds."

"The restoring force of an ideal spring is: Fx = k·x. Where k is the spring constant and x being the displacement."

"The larger the k value, the more force it takes to stretch or compress a spring."

Describe what you found confusing from the assigned textbook reading or presentation preview. Your description (2-3 sentences) should specifically identify the concept(s) that you do not understand.
"I'm a little bit confused by Hooke's law. I don't really get what it is or what it is used for."

"I could definitely use help with Hooke's law and applying the concepts to the equations."

"Hooke's law was a bit confusing. I just don't know how to use it."

"Describe Hooke's law a bit more."

"Stress and strain are a little confusing to me and would need some clarification on that along with Hooke's law."

"I would need more examples on how to use and comprehend Hooke's law better. The formula is pretty clear but I am scared to be confused on some cases."

"It was all very straightforward. Again, the only challenge I seem to encounter is becoming familiar with the new equations being presented."

"Nothing too confusing."

"Nothing really which is good."

What is the SI (Système International) unit for stress?
"Pa."

"N/m2 = Pascals."

Explain why strain is a unitless quantity.
"Because it's change in length over length."

"Strain is the change in length divided by the initial length. Since both quantities have the dimensions of length, the resulting quantity in unitless."

"Because it is a fractional length change."

"I am not entirely sure."

What is the SI (Système International) unit for Young's modulus?
"Pa, the same as stress."

"N/m2."

"Y?"

The __________ lengths of vertical suspension bridge cable are stretched by a greater amount ∆L from their original lengths.
shorter.   ******** [8]
longer.   *************************** [27]
(There is a tie.)   *** [3]
(Unsure/lost/guessing/help!)   ** [2]

The __________ columns of 2×4s support the least amount of force.
narrower (two 2×4s).   ******************** [20]
wider (three 2×4s).   ************ [12]
(There is a tie.)   ****** [6]
(Unsure/lost/guessing/help!)   ** [2]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.
"More elaboration on Hooke's law."

"I would love it if you could quickly go over the answer to the bridge cable question on this assignment. Thank you!"

"Can you go over the question with the 2×4s?"

"This is probably easier than I think, I just didn’t have too much time to go into it."

"Thank you for changing your lecture times next semester! You rock!"

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