You are Here: Home >< Maths

# M3 Circular Motion watch

1. Please could someone explain why it is the tension of the lower string you make zero instead of the upper string in order to find the maximum time period?

Thanks
Attached Images

2. (Original post by PhyM23)
Please could someone explain why it is the tension of the lower string you make zero instead of the upper string in order to find the maximum time period?

Thanks
Because otherwise you would have levitating balls
3. (Original post by Gome44)
Because otherwise you would have levitating balls
But is it not possible for the bottom string to stay taut without the top string so long as enough force is provided to keep the particle in the air? Or am I just being stupid?
4. (Original post by PhyM23)
Please could someone explain why it is the tension of the lower string you make zero instead of the upper string in order to find the maximum time period?

Thanks
Think about it as a physical system - the top string is always under tension, so the bottom string is your "giveaway", so to say.
5. (Original post by aymanzayedmannan)
Think about it as a physical system - the top string is always under tension, so the bottom string is your "giveaway", so to say.
Ah so does the fact that the string is inextensible have something to do with that? Seeing as the bottom string can't stretch to make the top string go slack?
6. (Original post by Gome44)
Because otherwise you would have levitating balls
LOL

basically the particle rotates at a contant radius so(as both strings are taut and inextensible) hence the faster it rotates the more the tension in the lower string so lowest possible angular velocity occurs when the tension in the lower string is zero
7. (Original post by PhyM23)
Ah so does the fact that the string is inextensible have something to do with that? Seeing as the bottom string can't stretch to make the top string go slack?
You can spot what Duke said from the equations of motions you have Probably the best answer you're looking for
8. (Original post by aymanzayedmannan)
You can spot what Duke said from the equations of motions you have Probably the best answer you're looking for
PRSOM

9. (Original post by PhyM23)
PRSOM

No worries! How's your M3 revision going by the way? I've just started past papers. Which paper is this from?
10. (Original post by aymanzayedmannan)
No worries! How's your M3 revision going by the way? I've just started past papers. Which paper is this from?
Sorry... Jan 2014 IAL.
11. (Original post by Zacken)
Sorry... Jan 2014 IAL.
oh noes, now I feel like I'm cheating xD
12. (Original post by aymanzayedmannan)
oh noes, now I feel like I'm cheating xD
Haha XD

It's going well thanks! The questions seem to be quite repetitive, so I've been doing IAL papers since they seem harder than the GCE ones...

How's your revision going, and how did you do with your January exams??
13. (Original post by PhyM23)
Haha XD

It's going well thanks! The questions seem to be quite repetitive, so I've been doing IAL papers since they seem harder than the GCE ones...

How's your revision going, and how did you do with your January exams??
Haha, that's good news for me this summer...

They were alright. I flopped FP1 (bad day ) - got 86, but an A* in M2 + 100 in S1. A mixed bag, but I'd prefer S1 and FP1 the other way around.
14. (Original post by aymanzayedmannan)
Haha, that's good news for me this summer...

They were alright. I flopped FP1 (bad day ) - got 86, but an A* in M2 + 100 in S1. A mixed bag, but I'd prefer S1 and FP1 the other way around.
Haha you're not alone! There's been a lot of talk about making exams harder in the UK because of these reforms etc. so I think we should both expect difficult papers...

I wouldn't worry about FP1 seeing as it can't contribute to an A*. But I remember when I did FP1 last Summer - I left out an Argand diagram question and only realised when I got home...when I remembered I just put my head on my desk in dispair. I was really surprised I still got 88 in it though!

But those are awesome results! You should have bags of confidence going into the Summer exams

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 26, 2016
The home of Results and Clearing

### 1,060

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. Keele University
Sun, 19 Aug '18
2. University of Melbourne
Sun, 19 Aug '18
3. Sheffield Hallam University
Tue, 21 Aug '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams