Re: [Phys-l] [ap-physics] The Swinging Bucket Problem

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

> > "how fast do I have to spin a bucket in a vertical circle to avoid 
> > water spilling out?" problem.  It's got plenty of 
> subtleties to help 
> > divide those who really understand the situation from the plug and 
> > chuggers (for instance, anyone who draws tension in as a 
> force on the 
> > water is probably not thinking too carefully about the situation).
> > . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
>
> I am puzzled by the obvious derision being heaped upon 
> someone who would include the tension in the string in his 
> analysis. The AHA! moment here is when one realizes that as 
> the speed is lowered the acceleration at the top is provided 
> less and less by the tension while the gravitational force 
> (weight) remains the same - eventually becoming the only 
> force needed to ensure the circular motion. I would suspect 
> that any approach which uses a free body diagram that does 
> not include tension is simply guess work on the student's part.
>
> Bob at PC
The string is not touching the water.  Hence the string is exerting no
force on the water.