Bubble Wrap Length

[newpotato]

How can you the length of a roll of bubble wrap without physically unrolling and measuring it?

[newpotato]

Sorry. How can you work out the length?

[grasscarp]

cut off a very thin strip of the top without unrolling - just go round and round - and then get out a tape measure.

[DrFilth]

or find a roll with a label on that tells you

like . 10 metres long by 300 mm wide

[nescio]

I was thinking of ordering a roll of bubblewrap, just to see what it came packaged in.

I'll get my coat...

[DrFilth]

nescio mine came in a clear plastic bag

[boxtops]

Mine came in a wrap with the length on a label.....

[gingejbee]

Scrivens: you would need weighing equipment with very good resolution for your idea...since bubblewrap weighs so little.
Also, wouldn't there be a (weighty) cardboard inner that it's wound on?

[gingejbee]

I don't have an easy solution...which is why I didn't post one.
Yours isn't any sort of solution unless a) you have a very sensitive digital balance and b) the roll had no cardboard inner.

[grasscarp]

I thought my solution was pretty easy for newpotato. With the strip he cut off he can then play pop the bubble wrap.

[Cathyhuns]

A reasonably simple formula is L = pi*N*(D+d)/2 where N = (D-d)/(2*t) is the number of wraps of tape of thickness t on a roll of diameter D (when full) around a core of diameter d. The formula represents the average of two estimates using the sum of circumferences of concentric circles (inside vs. outside diameters based on t). The summation formula 1+2+3+...+N = N*(N+1)/2 is needed to develop each estimate.

Or Google Calculating Length of Spiral

[heathfield]

After looking at Cathy's answer, I'd be tempted to simply unroll it into 1 metre ;ong folds, and count them.

[heathfield]

;ong = long

[mibn2cweus]

Count the number of bubbles in one unit length.

With a pin, pop each bubble in the roll individually keeping a tally, then divide the total number of pops by the number of bubbles counted in your reference unit length, the quotient being equal to the length of the roll in the unit length originally chosen.

[gingejbee]

...for which you'll have to unroll ?

[mibn2cweus]

No one said it would be easy ;o)

Alternatively, assuming a uniform distribution of bubbles one could, using the same formula, simply count the number of bubbles along one edge of the roll.

[gingejbee]

mibn: "no one said it would be easy"......but someone (the OP) DID say "without physically unrolling".

[jomifl]

Measure the diametre of the roll, measure the diametre of the tube it is rolled on, add the two together, divide by 2 and multiply by 3.142. This gives the average length of each turn/layer. Multiply this by the number of layers.

[mibn2cweus]

jomifl
Measure the diametre of the roll, measure the diametre of the tube it is rolled on, add the two together, divide by 2 and multiply by 3.142. This gives the average length of each turn/layer. Multiply this by the number of layers.
10:30 Fri 14th Feb 2014

Jom, Your formula works if we assume each layer is of uniform thickness. In practice the inner (shorter) layers are more compressed and so most layers will be somewhat shorter than the 'average' length assumed by your formula. Perhaps using the numerically rather than the calculated physically central layer as the one assumed to be of 'average' length would produce a more accurate result.

gingejbee, There's no need to unroll in order to count the number of bubbles on the exposed outermost layer, the length of which can be measured with a flexible tape or nearly approximated by multiplying the outside diameter of the roll by pi. If one is adverse to popping all of the bubbles, one need only count how many rows there are by counting the bubbles that appear along the exposed edge of the roll. Dividing the total number of bubbles along the exposed edge by the number of such bubbles along the edge of the outer most layer provides the multiple of the length of the outside layer to determine the total length of the roll.

Note: Measuring the diameter/circumference of the sheet as opposed to that around the protruding bubbles will improve the accuracy of your results.