The discussion revolves around determining the viscosity of oil using a falling ball viscometer setup. Participants are examining the relationship between the forces acting on a ball falling through a fluid and the parameters provided, such as radius, mass, density of oil, and terminal velocity.
There is an ongoing exploration of the problem with various interpretations being considered. Some participants have provided insights into the equations involved, while others express uncertainty about the implications of acceleration and time calculations.
Participants note that they have not yet covered certain concepts in their coursework, which may affect their understanding of the problem. The discussion also highlights the need for clarity on the assumptions made regarding forces and motion in the fluid.
Yes. This sounds like a falling ball viscometer test. It is often used to measure the viscosity of highly viscous fluids. You do a force balance on the ball, taking into account the buoyant force on the ball, the weight, and the drag force. The drag force of the fluid on the ball is given by the equations you wrote down. This is called Stokes' Law.Panphobia said:Homework Statement
Finding the viscosity of oil...
Homework Equations
η = b/(6∏r)
Fr = -bv
The Attempt at a Solution
The question only gives a radius, mass, density of oil, and terminal velocity. Is it possible to get the viscosity with the given information?
Panphobia said:Ok so I just saw that the velocity given was the terminal velocity so then Fr = mg, and you can figure out b and η pretty easily. What I do not understand is this, if you wanted to get the time it takes for this object to go from 0 to half the terminal velocity, how would you get the it if the acceleration of the object is not constant?
That's the solution to the equation I gave you with the buoyant force neglected and v(0) = 0. You did know that, in the equation I gave you, you were supposed to substitute a = dv/dt, right?Panphobia said:but this has nothing to do with getting the time for the ball to get to half of terminal velocity right? the terminal velocity = 4 cm/s, so half = 2 cm/s, even if I got the acceleration of the ball at that instant, that wouldn't bring me any closer to finding the time, right? Can v(t) = -(mg*e^((-b/m)t))/b + mg/b give me the right time?