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Mechanical Properties of Solids. Density. Physical property of matter The ratio of an objects mass per unit volume or ρ = m/V Variable is the Greek letter “rho” ( ρ ). Specific Gravity. The ratio of the density of an object compared to the density of water.
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Density • Physical property of matter • The ratio of an objects mass per unit volume or ρ = m/V • Variable is the Greek letter “rho” (ρ)
Specific Gravity • The ratio of the density of an object compared to the density of water. • ρH2O=1 g/cm3 = 1000 kg/m3
Elasticity - A value indicating a material’s ability to return to its original shape/form after a stress has been removed from it. SO...what is a stress???
STRESS • When a force is applied to an immobile object, the stress it experiences is the ratio of the force applied to the area over which it is applied. Ratio of force to the area over which it is exerted. • Stress = PRESSURE • Variable is (lower-case) “sigma” () • = F/A • Units: N/m2 or Pascal (Pa)
3 Main Categories of Stress • Tensile/Tension • Compressive/Compression • Shear/Torsion
Tensile Stress • Applied to an object when equal and opposite forces act away from each other on an object’s ends. • Results in a lengthening of a material.
Compressive Stress • Applied when equal & opposite forces act toward each other on an object’s ends. • Results in a shortening of a material.
Shear Stress • Applied when parallel forces have different lines of action. • Results in a twisting motion that changes the shape of an object, but not its volume.