Thursday, 14 March 2019

homework and exercises - Rolling bowling ball with slipping


If a bowling ball is moving with some initial velocity while slipping, how far will it move before it begins to roll once it experiences static friction?


¨x=μkfg


And there is also a torque from the kinetic friction on the ball (R = radius of the ball)


mgμkfR=2mR25¨θ¨θ=5gμkf2R


The condition for rolling without slipping is v=Rω and from the time the ball makes contact with the ground, transversal velocity decreases while angular velocity increases to a point where they are equal. I am not sure what I should do at this point, because everything I try doesn't seem to work.


¨x=vdvdx=μkfgv2=(2μkfg)x+v2o


I don't quite know what to do with this Differential equation that won't involve θ so that I can use it in the linear equation of motion. I have tried using time, but I don't know how that would help, And the actual angle itself is useless.


¨θ=5gμkf2R

I can't say x=Rθ because of the slipping



Answer




Lets say that when your ball first contacts the ground, it has initial velocity v0 and initial angular velocity ω0=0.


You have a constant torque being applied to the ball, so your differential equation is very easy to integrate to get:


˙θ=ω=5gμ2Rt+ω0


For the displacement, go directly with Newton's law, ¨x=μg, which also has a constant force and can be easily integrated once to get


˙x=v=v0μgt


From here you should be able to use your v=ωR condition to find out how long will it take the ball to start rolling without slipping, and once you have that time, integrate displacement once more to get


x=v0t12μgt2,


which will give you the distance traveled entering the time you calculated before.


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