# drag forces are functions of velocity , rather than functions of time. drag forces:

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Drag Forces: Non-Constant Forces that are Functions of Velocity. Drag forces are functions of velocity , rather than functions of time. Drag Forces: slow an object down as it passes through a fluid act in opposite direction to velocity vary with velocity or velocity squared - PowerPoint PPT PresentationTRANSCRIPT

Drag forces are functions of velocity, rather than functions of time. Drag Forces:slow an object down as it passes through a fluidact in opposite direction to velocityvary with velocity or velocity squareddepend upon the fluid and the projectile characteristicswill impose a terminal velocity if a falling object reaches a high enough speedDrag Forces: Non-Constant Forces that are Functions of Velocity

Drag as a Function of VelocityIn general, a drag force acts like a velocity-dependent kinetic friction. The general expression isfD = bv + cv2b and c depend uponshape and size of objectproperties of fluidb is more important at low velocityc is more important at high velocity

Drag Force in Free Fallwhen fD equals mg, terminal velocity has been reached

Drag Force in Free FallFor fast moving objects:

FD = c v2

c = 1/2 D r A

WhereD = drag coefficientr = density of fluidA = cross-sectional area of projectileFD = bv + c v2For slow moving objects:

FD = b v

mgFD

Practice Problem: For slow-moving objects, show that vT = mg/b, where vT is terminal velocity.

Practice Problem:For slow-moving objects, show that prior to attaining terminal velocity, the velocity of an object subjected to the drag force varies as:

Practice Problem: For fast-moving objects, show that terminal velocity is

Practice Problem: Derive an expression for the velocity of a falling fast-moving object as a function of time. The expression you derive should be valid prior to attainment of terminal velocity, as well as after terminal velocity is attained.

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