Glossary

deformation

change in shape due to the application of force

drag force

$F_{\text{D}}$, found to be proportional to the square of the speed of the object; mathematically

$$F_{\text{D}}\propto v^{\text{2}}$$

$$F_{\text{D}}=\frac{1}{2}\mathrm{C\rho }{\mathrm{Av}}^2,$$

where $C$ is the drag coefficient, $A$ is the area of the object facing the fluid, and $\rho$ is the density of the fluid

friction

a force that opposes relative motion or attempts at motion between systems in contact

Hooke’s law

proportional relationship between the force $F$ on a material and the deformation $\mathrm{\Delta }L$ it causes, $F=k\mathrm{\Delta }L$

kinetic friction

a force that opposes the motion of two systems that are in contact and moving relative to one another

magnitude of kinetic friction

$f_{\mathrm{k}}={\mu }_{\mathrm{k}}N$, where ${\mu }_{\mathrm{k}}$ is the coefficient of kinetic friction

magnitude of static friction

$f_{\mathrm{s}}\le {\mu }_{\mathrm{s}}N$, where ${\mu }_{\mathrm{s}}$ is the coefficient of static friction and $N$ is the magnitude of the normal force

shear deformation

deformation perpendicular to the original length of an object

static friction

a force that opposes the motion of two systems that are in contact and are not moving relative to one another

Stokes’ law

$F_{\mathrm{s}}=6\mathrm{\pi r\eta v}$, where $r$ is the radius of the object, $\eta$ is the viscosity of the fluid, and $v$ is the object’s velocity

strain

ratio of change in length to original length

stress

ratio of force to area

tensile strength

the breaking stress that will cause permanent deformation or fraction of a material