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M3 Vertical Circular Motion watch

1. With questions involving a particle moving in a complete vertical circle, is it the tension that has to be > 0 or v^2 that has to be > 0 at the top? I'll post an example if required..
2. (Original post by MathsAstronomy12)
With questions involving a particle moving in a complete vertical circle, is it the tension that has to be > 0 or v^2 that has to be > 0 at the top? I'll post an example if required..
Tension.
3. (Original post by Zacken)
Tension.
Then how come :

https://8a40d6c38bafca75cc407741c0f3...%20Edexcel.pdf (question 7b)

Mark scheme :

https://8a40d6c38bafca75cc407741c0f3...%20Edexcel.pdf
4. bump
5. I think maybe one is a necessary condition and the other is necessary and sufficient or something like that? I'm not entirely sure myself. Student403 will know.
6. (Original post by MathsAstronomy12)
With questions involving a particle moving in a complete vertical circle, is it the tension that has to be > 0 or v^2 that has to be > 0 at the top? I'll post an example if required..
The speed has to be > 0.
7. (Original post by EricPiphany)
The speed has to be > 0.
But then the particle could be moving freely under gravity, not necessarily remaining in circular motion..?
8. (Original post by MathsAstronomy12)
With questions involving a particle moving in a complete vertical circle, is it the tension that has to be > 0 or v^2 that has to be > 0 at the top? I'll post an example if required..
(Original post by Zacken)
Tension.
Depends on what the particle is attached to. If it is on the end of a rod or in a tube, it can't fall out of the circular path, so it is the speed that must remain positive (not to mention real). If it is on the end of a string or going round inside a hollow sphere, so that it can fall out of the circular path, it is the tension (or normal reaction) that must remain > = 0 (think the Simpsons movie).
9. (Original post by tiny hobbit)
Depends on what the particle is attached to. If it is on the end of a rod or in a tube, it can't fall out of the circular path, so it is the speed that must remain positive (not to mention real). If it is on the end of a string or going round inside a hollow sphere, so that it can fall out of the circular path, it is the tension (or normal reaction) that must remain > = 0 (think the Simpsons movie).
Aaaahh, that makes a ton of sense, thank you!
10. (Original post by MathsAstronomy12)
But then the particle could be moving freely under gravity, not necessarily remaining in circular motion..?
Accept that I would say that the speed > 0 is a condition that needs to be fulfilled either way.
The speed can never be < 0, if the maths says so, it'll never reach there.
And tension by definition is greater or equal to zero.
11. (Original post by tiny hobbit)
Depends on what the particle is attached to. If it is on the end of a rod or in a tube, it can't fall out of the circular path, so it is the speed that must remain positive (not to mention real). If it is on the end of a string or going round inside a hollow sphere, so that it can fall out of the circular path, it is the tension (or normal reaction) that must remain > = 0 (think the Simpsons movie).
Oh, so if it was at the end of a string, T > 0? That makes sense ish as in the question above, the particle is attached to a rod, the sneaky bugger

12. (Original post by MathsAstronomy12)
With questions involving a particle moving in a complete vertical circle, is it the tension that has to be > 0 or v^2 that has to be > 0 at the top? I'll post an example if required..
Yes. tiny hobbit explains it well..

Here is a summary from the Edexcel textbook. Basically the tension in a rod is irrelevant

13. (Original post by Student403)
Yes. tiny hobbit explains it well..

Here is a summary from the Edexcel textbook. Basically the tension in a rod is irrelevant

Okay, thank you
14. (Original post by Student403)
Yes. tiny hobbit explains it well..
I'm glad that all those years of teaching it have proved useful!
15. (Original post by tiny hobbit)
I'm glad that all those years of teaching it have proved useful!
I wish I had you to teach me M3 Self teaching was a nightmare..

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