 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
 ${f}_{\mathrm{s}}\le {\mu}_{\mathrm{s}}\phantom{\rule{0.25em}{0ex}}N$, 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