O000188 – Physics 2: Vibration, Waves and Thermodynamics
1st year of Joint Section Bachelor of Science in Environmental
Technology, Food Technology and Molecular Biotechnology
Chapter 10
The conditions for equilibrium
 For an object to be at rest, Newton’s second law states that the sum of the forces
must add up to __. This is the first condition of equilibrium.
o Σ𝐹𝑥 = ___, Σ𝐹𝑦 = ___, Σ𝐹𝑧 = ___
 For an object to be at rest, the net torque applied must be added to __.
o Σ𝜏 = ___
 In other words, the net force and net torque must equal __.
Stability and balance
 _____: The object returns to its original position.
 _____: The object moves farther from its original position.
 _____: The object remains in its new position.
Elasticity; Stress and strain
 Elasticity and Hooke’s Law
o 𝐹 = __ ∗ __
 Youngs Modulus
o ∆𝑙 = _____
o The Elastic moduli is same/different for different materials.
 Stress and Strain
𝐹𝑜𝑟𝑐𝑒
o Stress = 𝐴𝑟𝑒𝑎 = __
o Strain =

𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑙𝑒𝑛𝑔𝑡ℎ
𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ
= __
Relationship between Youngs Modulus, Stress, and Strain
𝑆𝑡𝑟𝑒𝑠𝑠/𝑆𝑡𝑟𝑎𝑖𝑛
𝐹/𝐴
o 𝐸 = 𝑆𝑡𝑟𝑒𝑠𝑠/𝑆𝑡𝑟𝑎𝑖𝑛 = ∆𝑙/𝑙
0
Tension, Compression, and Shear Stress
 When a rod is being stretched, it is under _____ stress.
 When a rod is being “squashed”, it is under _____ stress.
 When a book is being pushed parallel to the ground, it is under _____ stress.
 Shear Modulus
𝑙 𝐹
o 𝐺 = ∆𝑙0 𝐴

Bulk Modulus
∆𝑃
o 𝐵 = − ∆𝑉/𝑉
0
Fracture
 Safety factor
o If the safety factor for Aluminum is from 5 to 10, the actual stress on the
structure should not exceed _____ to _____.
Arches and Domes
 Arches and Domes are special ways to span a space that allow the ____ to be managed
well.