Physics 9: 5-7 Uneven forces on Rigid Bodies

Homework

Reading Preparation
Key Equations
WebLecture
Study Activity
Chat Preparation Activities
Chapter Quiz
Lab Work

Reading Preparation

Text Reading: Giancoli, Physics - Principles with Applications, Chapter 9: Sections 4-7

Study Points

9.5: Hooke's Law states that when something is stretched, the force acting on the body is proportional to the distance stretched, multiplied by some constant which depends on the material and its condition by an elastic modulus. At some point L becomes great enough that the material will snap. F = k * ΔL = (EAΔL]/L_o.
- We identify stress as the pressure on an object, force/area
- We identify strain as the change in length contrasted to the original length, ΔL/L_o.
- If we rewrite our force equation above as F/A = E ΔL/L_o, we discover that stress = elastic modulus * strain. The elastic modulus is also known as Young's Modulus.
- Shear stress deforms an object according to ΔL = FL_o/GA, where G is the shear modulus.
- Bulk changes if pressure is exerted from all sides, according to B = -ΔP/ΔV/v_o.
9.6: Fracture occurs when stress, strain, or shear forces break an object. In creating buildings, architects try to balance forces so that the greatest stress or strain on a materia is significantly less than the material's ability to withstand the forces acting in a given situation. It may make sense to use materials with high compressive strength as weight-bearing components, while other materials should be used if tensile forces or shear forces are at work.

9.7: Arches require that both downward and outward forces be balanced. Pillars must not only support the weight of the arch or dome, they must also push inward to compensate for the outward component working along the curve of the arch.

Each of the buildings below solves the problem of supporting a dome or high vault differently. [For more information, see Great Buildings Online.]
	Flying buttresses support the tower above the crossing at Chartres Cathedral (thirteenth century)
	The dome of St. Paul's, London (seventeenth century) rises 366 feet above its foundation; the interior and exterior domes hide a brick cone that provides the necessary support.
	Romanesque arches and extensions from the main building support the dome of the Pantheon, Paris (18th century)

Key Equations

Hooke's Law $F = k Δ x$
Young's Modulus $Δ L = \frac{1}{E} \frac{F}{A} L_{0}$
or $E = \frac{\frac{F}{A}}{\frac{Δ L}{L_{0}}}$
Shear Stress $Δ L = \frac{1}{G} \frac{F}{A} L_{0}$
Bulk Modulus $\frac{Δ V}{V} = - \frac{1}{B} Δ P$

Web Lecture

Read the following weblecture before chat: Inertia, Acceleration, and Force

Study Activity

Use the Young's Modulus simulation to measure strain and stress on wires of different materials. Work through the theory tab introduction, and read the procedure for the lab. You can watch a sample lab on the YouTube video, then use the simulator.

With the simulator, devise and conduct a test to determine how materials behave in an Earth environment.

behavior changes as weight changes (holding material, radius, and length constant).
behavior changes as wire radius changes (holding material, weight, and length constant)
behavior changes as wire length changes (holding material, weight, and radius constant)

https://amrita.olabs.edu.in/?sub=1&brch=5&sim=155&cnt=4

Chat Preparation Activities

Forum question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.

Chapter Quiz

Required: Complete the Mastery exercise with a passing score of 85% or better.
Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!

Lab Work

If you want lab credit for this course, you must complete at least 18 labs; you may complete more if you are preparing for the AP exam.. One or more lab exercises are posted for each chapter as part of the homework assignment. We will be reviewing lab work at regular intervals, so do not get behind!

Lab Instructions: Structural Integrity

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Physics

Chapter 9: 5-7 Assignment