CHAPTER 13. 평형과 탄성 13. 1 평형 (Equilibrium) 13. 2 평형 조건 13. 3 중력 중심 (Center of Gravity) 13. 4 정적 평형의 예 13. 5 불확실한 (Indeterminate) 구조 13. 6 탄성 (Elasticity)

: Static Equilibrium (정적 평형) Section 8-5

13-2 평형 조건 병진운동 : 회전운동 : (balance of force) (balance of torques) 2 차원 13-2 평형 조건 병진운동 : (balance of force) 회전운동 : (balance of torques) 2 차원 일정한 속도로 미끄러지는 Hockey puck

13-3 중력 중심 (Center of Gravity) Center of Mass = Center of Gravity

13-4 정적 평형의 예 Scale readings?

Find Tc and F on the hinge.

Rock climber resting Find N, and h. Best position to rest.

13-5 Indeterminate Structure For 2-dimensional problems, 2 Fx, Fy 1 z 3 unknowns  solvable What if we have 4 unkowns?  indeterminate Need elasticity to solve them!

Spring model of atomic “lattice” 13-6 탄성 (Elasticity) Spring model of atomic “lattice” Tensile stress (인장 변형력) (b) Shearing stress (층 밀리기 변형력) (c) hydraulic stress

Stress = modulus x strain constant of proportionality = modulus of elasticity Tension and Compression (인장과 압축) Ultimate Strength의 차이 : 콘크리트 : 압축 (강) 장력 (약)

층 밀리기 : 체적의 변형 :

Find Stress, elongation and strain of the rod. At the bottom of the Pacific Ocean, p = ~ 4107 N/m2 (~ 4000 m 깊이) B(water) = 2.2109 N/m2 and B(steel) = 161010 N/m2 Find Stress, elongation and strain of the rod. 81 cm R=9.5 mm F = 6.2 104 N F