Mechanical Properties of Solids

Density Physical property of matter Physical property of matter The ratio of an objects mass per unit volume or ρ = m/V The ratio of an objects mass per unit volume or ρ = m/V Variable is the Greek letter “rho” ( ρ) Variable is the Greek letter “rho” ( ρ)

Specific Gravity The ratio of the density of an object compared to the density of water. The ratio of the density of an object compared to the density of water. ρ H 2 O = 1 g/cm 3 = 1000 kg/m 3 ρ H 2 O = 1 g/cm 3 = 1000 kg/m 3

Elasticity - A value indicating a material’s ability to return to its original shape/form after a stress has been removed from it.

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. 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 Stress = PRESSURE Variable is (lower-case) “sigma” (  ) Variable is (lower-case) “sigma” (  )  = F/A  = F/A Units: N/m 2 or Pascal (Pa) Units: N/m 2 or Pascal (Pa)

3 Main Categories of Stress Tensile/Tension Tensile/Tension Compressive/Compression Compressive/Compression Shear/Torsion Shear/Torsion

Tensile Stress Applied to an object when equal and opposite forces act away from each other on an object’s ends. 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. Results in a lengthening of a material.

Compressive Stress Applied when equal & opposite forces act toward each other on an object’s ends. Applied when equal & opposite forces act toward each other on an object’s ends. Results in a shortening of a material. Results in a shortening of a material.

Shear Stress Applied when parallel forces have different lines of action. 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. Results in a twisting motion that changes the shape of an object, but not its volume.