Newton's law for the viscous friction. What does the derivative of the velocity (dv)/(dr) mean in the formula? Change of the fluid velocity over time Change in the velocity of fluid flow in the direction. perpendicular flow of liquid Change in the velocity of the liquid flow along the tube

The correct answer is: Change in the velocity of the liquid flow along the tube.<br /><br />In Newton's law for viscous friction, the derivative of the velocity $\frac{dv}{dr}$ represents the change in the velocity of the liquid flow along the tube. This derivative indicates how the velocity of the fluid changes with respect to the distance from the center of the tube. It is a measure of the velocity gradient in the fluid flow, which is a crucial factor in determining the viscous forces acting on the fluid.