How Does Weight Affect the Stretch Length of Rubber Bands?

[jungboho]

rubber BANDS

hi guys
i was just wondering what the relationship between the weight and stretch length of rubber is. And also why does an 8cm rubber band increase it's stretch length by 5cm at 600gms weight while the trend before and after is every 10gm added to the weight adds 0.2 to to the lenght.

 

[Integral]

could you post your data? I am not sure I understand what you are seeing.

 

[jungboho]

ok
it may take me a while to obtain it

 

[StephenPrivitera]

I'm not sure what you're getting at, but I noticed once that if you take one of those strings you sometimes attach to light bulbs and stretch it 3 or 4 inches, it will hit the ceiling when you release it. There must be a great deal of potential energy associated with the string. I haven't played with rubber bands recently, but my guess is they act similarly. They obviously don't obey hooke's law.
I think that's what you're getting at anyway.
You should be able to determine the relationship to some degree yourself through experiment.

 

[jungboho]

God I need help

please help me with rubber bands the graph is amount of extension v weight

I have been having trouble with this for ages

 

[jungboho]

i'm back with my data

 

[russ_watters]

One data point off in the middle of nowhere is usually a sign of error.

 

[NateTG]

Can you provide more context?

 

[Loren Booda]

Elasticity can be assumed to first approximation to obey F=kx, the "spring" equation. Replacing the force F with mg, we have mg=kx, where m is the hanging mass, g the local acceleration of gravity, k is the spring constant, and x is the displacement downward. Since g and k are considered constant, m varies directly as x.

 

[Integral]

What do you need to do with it?

Looks like you have an error (perhaps droped decmial point) should that "outlayer" be .6 rather then 6?

Looks like you have the data in Excel, you can do a linear regression to get the best fit line. I would use the data from about 200 up, as below that there is very little change.

As I Recall you will need to learn to create an ARRAY FORMULA to use the Linest function.
select 2 adject cells and enter
=LINEST(A6:A19,B6:B19)
replace the specified ranges with your data location.

prese ctrl-shift-enter.

This will give you the slope and intercept of the data.

 

[Loren Booda]

After the linear elastic region, there is a critical point in strain whereafter nonlinearity leads to failure of the specimen.

 

[Spectre5]

yea, are you sure you did not mean to have that value .6??

 

[jungboho]

yep incredibly sure

I have repeated the experiment a few times the jump always happens though in varying amounts.

 

[jungboho]

email me at jungboho@hotmail .com for the full method and excel document

 

[jungboho]

email me for full methond and orginal excel document

jungboho@hotmail.com

 

[russ_watters]

Originally posted by Loren Booda
After the linear elastic region, there is a critical point in strain whereafter nonlinearity leads to failure of the specimen.

That's true, but the critical point is at a the point of a shape change of the curve, not a transiant jump in one value. The curve remains continuous.

 

[jungboho]

strange isn't it
This was physics coursework but ow it's transcended into something more

 

[Integral]

It seems that you are plotting the CHANGE in length. Since the basic relationship is f=-kx it would be more meaningful to plot the total length, that would change your spike to a step, much easier to understand. Also it would give physical meaning to the slope of your data.

 

[Loren Booda]

jungboho

strange isn't it
This was physics coursework but ow it's transcended into something more

Ow indeed! Welcome to the universe of Physics.

 

[pallidin]

Hmmm. I was under the impression that a uniform rubber band requires increasing force to stretch it further than its previous point. So, to suggest that a certain amount of force always increases length by a constant amount after a given stretch point makes no sense to me in my experience with rubber bands.
Indeed, does not a rubber band increase its resistance to extension the more it is pulled?
Anomalies to this might be encountered if the rubber band was not dimensionally uniform(what rubber band truly is), or if the rubber band in processing has variant elasticsity due to poor manufacturing(common; look closely at a band and one sometimes finds regions of more dense rubber), or random chemical contaminants which change local elastic properties.

 

[Integral]

Pallidin,
To the best of my knowledge you are correct, rubber bands are not very good Hooks law springs. I feel that the plot of total length vs total force would show this very clearly.

 

[Integral]

Threads merged.

We only need one thread on this topic. I have combined and added information to the thread title.