Ch 12 Static Equilibrium and Elasticity Forces and

Ch. 12: Static Equilibrium and Elasticity (Forces and Torques are balanced AND Deformation due to applied stress) *All materials become distorted when squeezed or stretched with enough force

3 Types of Elasticity: F 1) Tension / Compression F 2) Shear Deformation 3) Volume Deformation F

1) Tension / Compression A L 0 F L A = area to applied force Y = Young’s modulus (depends on the material) *The same equation holds for compression ( L = decrease in length)

Ex: Weightlifter a) If he is lifting a total of 500 lbs, and his forearms are each. 30 m long with cross sectional bone area of 6. 0 x 10 -4 m 2, by how much does each bone compress? b) By how much does each bone stretch if he suspends the same weight with his arms hanging downward?

2) Shear Deformation S = Shear modulus (depends on the material)

Ex: Jello . 07 m 6. 0 mm When a shear force of. 45 N is applied . 03 m Use this information to find the shear modulus of jello

3) Volume Deformation *SI unit = N/m 2 = 1 Pascal V = change in volume change in pressure V 0 = initial volume B = Bulk modulus (depends on the material)

Ex: Styrofoam cup

The formulas for all 3 types of elasticity can be arranged to look very similar…… Stretching: Shearing: Volume: Stress Strain *Applies only up to the elastic limit (then it breaks) Another form of Hooke’s Law