Question about Angular Motion in a horizontal plane

[sodnaz]

For finding the critical speed or the minimum speed in a question for a vertical plane, you take either the friction or the contact (normal) force to be 0, so F=W

However, for a horizontal plane, like spinning something around in a circle, you can still do F=W to find the critical speed or the minimum speed. Why is this? I know that for a horizontal plane, the tension is equal to the centripetal force, but why can you still just equate F=W to find V that way, when tension is the centripetal force.

 

[berkeman]

For finding the critical speed or the minimum speed in a question for a vertical plane, you take either the friction or the contact (normal) force to be 0, so F=W

However, for a horizontal plane, like spinning something around in a circle, you can still do F=W to find the critical speed or the minimum speed. Why is this? I know that for a horizontal plane, the tension is equal to the centripetal force, but why can you still just equate F=W to find V that way, when tension is the centripetal force.

Welcome to the PF.

Can you post a couple diagrams for what you are asking about? For the vertical case, it sounds like you are asking about the minimum speed to spin a mass on the end of taut string, but then you mention friction... And for the horizontal case, what do you mean by "critical speed"?

 

[sodnaz]

Welcome to the PF.

Can you post a couple diagrams for what you are asking about? For the vertical case, it sounds like you are asking about the minimum speed to spin a mass on the end of taut string, but then you mention friction... And for the horizontal case, what do you mean by "critical speed"?

Sorry, my mistake. For the vertical case, I meant to say tension and not friction. For the horizontal case, ignore where I said 'critical speed' and replace that with the minimum speed for the mass to spin on the end of a taut string again, so that it stays spinning and the velocity isn't small enough that it stops spinning and falls out of it's 'orbit' (so to speak)