[neilep]

Yes I agree with the maestro because I hear he's a swinger and a part time Tarzan !!....at the bottom of the arc....and if it's not...then it should be !!...

HANG ON !!....just before I press ' submit ' I may feel inclined to change my mind and say it's when the rope is half way between the bottom of the swing and the end of the swing because at that point the person will want to continue going on in a straight line .....and I'm just picturing in my head where I have seen people fall of swinging ropes !!...it's usually half way up the arc..because of Momentum...or is it Inertia ?...it's one of those two...Yes..Momentum will try to yank the person off the rope and snap it at that point....I think.  Say the bottom of the swing is 6 'o' clock and the end of the swing is 3 and 9 'o' clock then the rope will break between 7 and 8 or between 4 and 5.

Men are the same as women.... just inside out !!

[ukmicky]

No its at the bottom point where the downward motion of the swing suddenly changes to upwards movement creating positive g'forces

Michael

[neilep]

quote:Originally posted by ukmicky

No its at the bottom point where the downward motion of the swing suddenly changes to upwards movement creating positive g'forces

Michael

[]OK OK Keep your hair on !![]...actually I'm about to get my hair shaver and go down Bald Avenue again  !!..

HMmm it seems the rope fairies have misinformed me then....well, i'm guessing anyway but you sound so sure..so..i'm convinced too .....[]

Men are the same as women.... just inside out !!

[ukmicky]

I could be wrong, it has been known

Michael

[DoctorBeaver]

Most likely at the point where I get out my machete because my friend is filming it for "You've Been Framed" & I want the £100 or however much it is these days. []

[ukmicky]

Doc your back, nice to see

Michael

[sharkeyandgeorge]

i have broken many many tarzan swings and 90 percent of the time the rope breaks not at the top of the ark but just as you start to swing back some thing do do with the change in centrifugal force perhaps?

"Defender of the Sea"

[chris]

Ok, this was a hard one to explain, but here's the solution to:

"AT WHAT POINT IN ITS ARC IS A ROPE SWING MOST LIKELY TO BREAK?"

The simple answer is at bottom dead centre. At this point the kinetic energy of the swing and passenger is at its greatest, and the effect of gravity is acting straight down through the rider on all of his weight. So the swing is most likely to break at the mid point of its travel.

Now for the more complicated proof of concept.

If we consider a swing (and rider) which together have a mass of m suspended on a cord of length L (with negligible mass), swinging through an angle of x degrees (where 0 degrees is the horizontal).

Lets assume that the swing begins held out at 90 degrees i.e. horizontal (admittedly a scary ride!). Starting from this point, the speed of the swing at any point in its subsequent arc of travel will be such that the kinetic energy (0.5 * m * velocity(v) ^ 2) is equal to the change in potential energy from its starting point. The change in potential energy will be:

the mass of the swing and rider(m) * gravity * L * sin(x)

So 0.5 * m * v^2 = m * g * L * sin(x)

hence v^2= m * g * L * sin(x)/0.5 * m

hence v^2= 2 * g * L * sin(x)

Now the pull exerted by the swing on the rope is given by the formula speed squared / radius of arc, or v^2 / L (length of swing rope).

So the pull here is v^2 / L which equals 2 * g * sin(x).

The contribution due to gravity at any point along the travel will be g * sin(x).

Since F (tension in the string)= m * a

then the tension (T) must be m * ((2 * g * sin(x) + g * sin(x))

which equals 3mg sin(x).

So, at any point the tension in the rope supporting the swing will be 3 * mass of swing and rider * sin(angle travelled).

If we substitute into this formula, sin(0) - horizontal - is 0, so at thte start point, when the speed is zero, there is no tension on the rope.

One third of the way to the bottom dead centre (30 degrees), sin(30) = 0.5 so the tension is 3mg * 0.5

Two thirds of the way to the bottom (60 degrees), sin (60) = 0.666667 so the tension is 3mg * 0.666667

And at the bottom (90 degrees), sin (90) = 1 so the tension is 3mg. This is the maximum. So the rope has to be capable of holding three times the rider's weight.

I hope that helps to lay that one to rest.

Chris

[chris]

Okay, here's this week's QOTW:

"WHAT IS A HOLOGRAM, AND HOW ARE THEY MADE?"

Have a go, below.

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[neilep]

It's a telegram with no substance whatsoever []



ps: Well done Michael..I reckon you got the ropey question right...with no strings attached of course !! []

Men are the same as women.... just inside out !!

[DoctorBeaver]

Neil - that was almost bad enough to be mistaken for 1 of mine!

On a serious note, a friend of mine set himself up as a Hollergram. Instead of singing the message to people, he shouted it at them!

[neilep]

Eth, Mine don't even come close...[]

Hollergram .....agghhhhh !!..see ?

Men are the same as women.... just inside out !!

[DoctorBeaver]

Or what about a Holagram who just says "hello" to you in Spanish?

[Ray hinton]

or a HALOGRAM,just does it while you tend your flocks by night [:0]

its the drugs,y-know.

[DoctorBeaver]

That's silly

[ukmicky]

quote:originally by ukmicky
 At the bottom of the arc i would have thought

 

quote:The simple answer is at bottom dead centre.

Chris

HMMM its not often i get things right but occasionally i astound myself and others and produce the goods.

Where's my congratulations, where's my prize. i want my goody bag []

Michael

[clouded.perception]

Charmeleons have different coloured cells in their skin. To change colour, they 'open up' the cells with the correct pigment, thus showing that colour (or combination of colours) on their skin.

I can picture in my mind a world without hate, a world without war.
And I can picture us attacking that world, because they'd never expect it.

[chris]

That's very nice, but this week's question is about HOLOGRAMS!

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[JimBob]

Split a laser beam, record the interference pattern made when this beam shines on an object from two different directions. (It's doned with smoke and mirrors.) Project the record to make the same interferance pattern and shine coherent light on it. Presto, a 3D Hologram.

Perhaps this was ignored because it is so easy. These thngs have been around since the 50's. (I wasn't around then - I was a Science Attache at the Klingon Embassy in Star Cluster 4289-F.)  

Jim

[ampwelder]

Hologram come from the greek words "whole" (holo) and writing (gram).
  A lazer is used to photograph an object (instead of incoharent-normal- light) it does this in such a way that enough information can be recorded to give the imprestion of a 3-D object. This is an illusion as the holograph is actually only 2-D like a regular picture.