Quantitative centripetal force apparatus-free body diagram

[prowler_sn]

hi there i was looking at this video on utube and have two questions regarding it.


at 1:02. the person starts to rotate the apparatus. my first question is that HOW CAN U DRAW THE FREE BODY DIAGRAM OF THE MASS ATTACH TO THE SPRING while its rotating?
i know there is the mg downward from the mass. there is the tension force pointing towards the spring and another tension force up in the string the mass is attach to. am i missing anything?

an other question is that what is the purpose of the counter mass?

thanks in advance

cheers

p.S this is NOT a homework question

 

[elegysix]

The counter mass balances the other mass... if you only had one, the centripetal force would pull the stand over if you went too fast.

Draw the free body diagram of it at one instant in time - basically the stand, spring and mass. You only need to draw the forces on it, not the actual rotation. Centripetal acceleration always points inwards, so its not changing in that sense.