Stokes drag force

Figure 2. (Left) Experimental setup in force flow measurements. Optical tweezers are used to trap beads but forces are applied on the RNApol-DNA molecular complex using the Stokes drag force acting on the left bead immersed in the flow. In this setup, force assists RNA transcription as the DNA tether between beads increases in length as a function of time, (a) The contour length of the DNA tether as a function of time and (b) the transcription rate as a function of the contour length. Pauses (temporary arrests of transcription) are shown as vertical arrows. (From Ref. 25.) (See color insert.)...

If Kn is not assumed to be zero, then the Stokes drag force on the particle also must be corrected for a slippage of gas at the particle surface. Experiments of Robert Millikan and others showed that the Stokes drag force could be corrected in a straightforward way. Using the theory of motion in a rarified gas, the mobility takes the form ... 

Epstein [1988] develops the concept of a particle in free flight with an initial velocity of subject to Stokes drag forces as it travels through a fluid. 

Figure 12.6 Calibration of trap stiffness using Stokes drag. The stiffness of the trap can be determined using Stokes drag force. A triangle wave is applied to the stage which holds the specimen chamber while a bead is held in the optical tweezer. The rapid movement of the stage creates a force, F, on the bead caused by the motion of the surrounding fluid. This causes the bead to be displaced a distance, x, from the trap centre the greater the system stiffness the less the bead is displaced. f/X= stiffness of the tweezers K) (inset)...

Fig. 3 Dimensionless charges of aqueous droplets. Charges are estimated from droplet velocities, and the Stokes drag force is adopted. Scaling law of charging for the deionized water droplets (bottom). The reference state was chosen as Oo = 276 pm,...

Balancing the viscous Stokes drag force (p drag) acoustophoretic force (Fy ) results... 

From fluid mechanical calculations, if the velocity field around the collector in the absence of the colloidal particles is known, then Vp, the velocity field of the particles, can also be found, at least to a good approximation. Moreover, the particle diffusion coefficient becomes position dependent since the Stokes drag force used to derive Equation 3.72 is modified by the presence of the nearby collector surface. The conservation equations (Equations 3.75 and 3.77) must therefore be replaced with the appropriate one ... 

Stokes drag force per bubble = force = Stt/uvsD power per bubble = force x velocity =... 

A particle suspended in a fluid is subjected to hydrodynamic forces. For low Reynolds number, the Stokes drag force on a spherical particle is given by... 

For very small particles, when the particle size becomes comparable with the gas mean free path, slip occurs and the expression for drag must be modified accordingly. Cunningham obtained the needed correction to the Stokes drag force ... 

---