Question about Angular Motion in a horizontal plane

AI Thread Summary
In discussions about angular motion in horizontal and vertical planes, the critical or minimum speed for an object in circular motion can be determined by equating force to weight (F=W). In vertical motion, this typically involves considering the tension or normal force when calculating minimum speed. For horizontal motion, tension acts as the centripetal force, allowing the same F=W approach to find the minimum speed necessary for the object to maintain its circular path. The clarification emphasizes that the term "critical speed" should be replaced with "minimum speed" to accurately describe the conditions for maintaining circular motion. Understanding these principles is essential for analyzing motion dynamics effectively.
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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