Force tends to alter object structure. Force can apply over area {pressure, physics}|. Pressure P equals force F per unit area A: P = F/A. Pressure P is energy E divided by volume V: P = F/A = (F*s) / (A*s) = E/V. Pressure is energy density: P = F/A = F / s^2 = F*s / s^3 = E/V.
Force causes structure change {strain}| in force direction. Pressure changes length. For example, gravity pulls feet into floor and tends to flatten feet, shoes, and floor. Strain is proportional to stress.
Force and pressure {stress, physics}| tend to alter object structure. I-beam, twisting torsion bars, and standing up use material stresses, strains, and strengths.
Mechanical forces {compression}| can be pushes on materials.
Mechanical forces {tension, force}| can be pulls on materials.
Mechanical forces {torsion, force}| can be twists on materials. Torsion is simultaneous push in one direction and pull in another direction.
Stress S is proportional to length change dL divided by length L {Hooke's law} {Hooke law}: S = k * (dL / L). Pressure compresses material against restoring force. Restoring force F varies with material type k and distance compressed x: F = -k * x. Pressure is compression force F divided by area A: P = F/A. Pressure equals restoring force -k*x divided by area A: P = F/A = -k * x / A. Constant k depends on Young's or other elasticity modulus u, cross-sectional area A, and object length L: k = A * u / L.
If pressure exceeds limiting value {elastic limit}|, material inelastically changes shape permanently. Higher temperature lowers elastic limit.
If pressure is less than elastic limit, material returns to original shape after removing pressure {elasticity, physics}|. Elasticity can be bulk strength, shear strength, or tensile strength. Elasticity varies for different material axes.
If pressure exceeds elastic limit, material changes shape permanently {inelasticity}|.
Elastic modulus reciprocal {compliance}| can indicate shape-changing ease.
Elasticity {Young's modulus, elasticity} {Young modulus, elasticity} varies for different material types. Steel is hard and bouncy and has high Young's modulus. Wood is soft and has low Young's modulus.
Elasticity varies for compression {bulk strength}|.
Elasticity varies for torsion {shear strength}|.
Elasticity varies for tension {tensile strength}|.
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Date Modified: 2022.0225