Problem
You're frustrated after studying for your (insert subject other than biophysics) midterm and throw your eraser at your freshly painted, very sticky wall. The eraser sticks to the surface of the wall, and takes 1 second to slip down the ~2 meter wall.
Being a fan of physics, you realize that you can model this as two parallel plates (wall and eraser) separated by a viscous fluid (paint). A quick google search shows you that the ~50???? thick paint layer on your wall should have a viscosity of 0.1 ???? ?? and a mass density of 1300 ????/??3.
I. According to the above values, and assuming the physics is well described by two parallel plates, what should be the slipping velocity of the eraser, knowing it has a mass of 30 g and dimensions of 3cm by 5cm?
II. Why is the calculated velocity so different to the observed velocity? Support your answer by calculating the critical force.