# Glossary

deformation
change in shape due to the application of force
drag force
FD, found to be proportional to the square of the speed of the object; mathematically
FD∝v2
FD=12CρAv2,
where C is the drag coefficient, A is the area of the object facing the fluid, and ρ 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 ΔL it causes, F=kΔL
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
fk=μkN, where μk is the coefficient of kinetic friction
magnitude of static friction
fs≤μsN, where μs 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
Fs=6πrηv, where r is the radius of the object, η 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
measure of deformation for a given tension or compression