Are Rubber Bands in Parallel Affected by Spring Constant?

[dilpreet28]

Hey

I am doing an experiment, checking how the spring constant of a rubber band relates to the spring constant of rubber bands in parallel. I calculated the gradient of a F vs x, graph i got a -0.0853 for the first rubber band, -0.0791 & -0.088 for the 2nd and the 3rd. Then i did them in parallel and did the same graph and got a constant value of -0.022.
This is confusing because i though that k(total) = k(1) + k(2) + k(3), for springs in parallel shouldn't this also apply to the rubber bands?

Thanks

 

[tiny-tim]

welcome to pf!

hey dilpreet28! welcome to pf!

… I calculated the gradient of a F vs x, graph i got a -0.0853 for the first rubber band, -0.0791 & -0.088 for the 2nd and the 3rd. Then i did them in parallel and did the same graph and got a constant value of -0.022.
This is confusing because i though that k(total) = k(1) + k(2) + k(3), for springs in parallel shouldn't this also apply to the rubber bands?

hmmph, that's odd …

three bands pulling side-by-side obviously give more force for the same extension

are you sure it wasn't -0.22 ?​

 

[dilpreet28]

Ahhh, i realized that i had force on the x axis, so i was calculating x/F so 1/k, when i switched the axis it worked.
Also i had another question, can i apply the formula for polymers F = (k*T*x)/L where t= temperature, x = length stretched, L = length of polymer, as rubber bands are made out of a couple of polymers would i be rationalise rubber bands using that formula instead of hooke's law as rubber is a non-hookean material?

 

[tiny-tim]

Ahhh, i realized that i had force on the x axis, so i was calculating x/F so 1/k, when i switched the axis it worked.

he he

Also i had another question, can i apply the formula for polymers F = (k*T*x)/L where t= temperature, x = length stretched, L = length of polymer, as rubber bands are made out of a couple of polymers would i be rationalise rubber bands using that formula instead of hooke's law as rubber is a non-hookean material?

oooh i don't know

i had no idea rubber bands were so complicated

 

[Pythagorean]

I'd think you'd have to couple several polymers together in a network to really simulate a rubberband.

Let's do the thermodynamic output of stretching too.

 

[dilpreet28]

Yea i know that i would have to take into account that there are multiple polymers in a rubber band, i just not some research backing me up on the experiment, i can't seem to find anything on the internet that states anything about the relationship of rubber bands being linera or what sort of law they follow and the polymer thing is the closest i have come to in terms of theories.

By the thermodynamic out of stretching did you mean the heat that is produced by the rubber bands and when it's un-stretched it absorbs heat, thus making if feel cool

 

[Pythagorean]

I think heneryobio is a spambot

Yea i know that i would have to take into account that there are multiple polymers in a rubber band, i just not some research backing me up on the experiment, i can't seem to find anything on the internet that states anything about the relationship of rubber bands being linera or what sort of law they follow and the polymer thing is the closest i have come to in terms of theories.

By the thermodynamic out of stretching did you mean the heat that is produced by the rubber bands and when it's un-stretched it absorbs heat, thus making if feel cool

I'm fairly sure both stretching and contracting the membrane produce heat.

chapter 9 has polymer networks:
http://onlinelibrary.wiley.com/doi/10.1002/0471757128.fmatter/summary

 

[dilpreet28]

Hmm.. i'll look into that

with the equation above(k=C=constant) F = (k*T*x)L
could i take out T and L as they are constant? so F=k*x?
is that reasonable or do i have to say F = C*k*x where c = T/L ?
Because I'm saying that in the experiment the length of the rubber band was same all the time and the temperature was negligible so do i still take those into account?