Question about Angular Motion in a horizontal plane

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SUMMARY

The discussion focuses on calculating the minimum speed required for an object to maintain circular motion in both vertical and horizontal planes. In vertical motion, the critical speed is determined by setting the friction or normal force to zero, equating force (F) to weight (W). For horizontal motion, the same principle applies, where tension acts as the centripetal force, allowing the use of F=W to find the minimum speed (V) necessary for the object to remain in circular motion. Clarifications were made regarding the terminology used, particularly distinguishing between tension and friction in these scenarios.

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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.
 
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sodnaz said:
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. :smile:

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"?
 
berkeman said:
Welcome to the PF. :smile:

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)
 

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