Does Teaching by Numbers Limit Understanding of Elasticity in Rubber Bands?

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Discussion Overview

The discussion revolves around the elasticity of rubber bands, particularly focusing on how prolonged stretching affects their elasticity and the implications of teaching methods that emphasize numerical data. Participants explore various aspects of rubber band behavior, including practical testing methods, definitions of elasticity, and the limitations of traditional educational approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether a rubber band loses its elasticity over time when kept in a stretched position, seeking to understand the time frame for such a change.
  • Others note that rubber bands can become dry and brittle with age, suggesting that older rubber bands may not be found in use.
  • A practical testing method is proposed where a rubber band is hung with a weight, and the movement of the weight is observed over time, with some participants noting temperature effects on the results.
  • Discussion includes the S-shaped force-extension curve of rubber bands, with references to Hooke's Law and the behavior of materials under stress.
  • Participants express uncertainty about the definition of "elasticity," indicating that it is a complex concept that may not be adequately conveyed through numerical teaching methods.
  • Some contributions emphasize that teaching by numbers may limit deeper understanding of material properties, suggesting that textbook representations can be insufficient.

Areas of Agreement / Disagreement

Participants generally express multiple competing views regarding the effects of prolonged stretching on rubber band elasticity and the adequacy of numerical teaching methods. The discussion remains unresolved, with no consensus on the definitions or implications of elasticity.

Contextual Notes

Participants highlight the complexity of defining elasticity and the potential limitations of educational approaches that focus solely on numerical data. There are references to the need for a deeper exploration of elastomer mechanical properties and the challenges in conveying these concepts effectively in a classroom setting.

Josh0768
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If you take a rubber band and fix it in a stretched position for an extended period of time, would it eventually lose its elasticity? If yes, then how can you calculate how long it would take until its elasticity decreases by a certain amount, say, fifty percent? If no, why not? How does the rubber band constantly maintain elasticity?
 
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Rubber bands become dry and brittle with time.

How old are you? My guess is that you don't find 50 year old rubber bands in the drawers of your office. :wink:
 
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anorlunda said:
My guess is that you don't find 50 year old rubber bands in the drawers of your office.
I saved the rubber bands that came wrapped around the daily newspaper. How old does that make them/me? I just now tried stretching a few, and only one broke and zapped my fingers.

The science of Rubber elasticity.
 
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There's an easy way to test :

Hang the rubber band from a hook next to a wall.
Hang a weight on the rubber band.
Mark the wall.
Wait.
 
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hmmm27 said:
Hang the rubber band from a hook next to a wall. Hang a weight on the rubber band. Mark the wall. Wait.
The weight will move up or down with the temperature.
 
hmmm27 said:
There's an easy way to test :

Hang the rubber band from a hook next to a wall.
Hang a weight on the rubber band.
Mark the wall.
Wait.
Keith_McClary said:
The weight will move up or down with the temperature.

a tiny fraction, but nowhere near as much as it's stretching due to the loss of elasticity

It's a good and easy practical test
 
We learn Hooke's Law at school but it's only later that we seriously examine what happens to rubber bands (and plastic bags). That S shaped curve of force against extension of a rubber band is easy to obtain with a home experiment. It's a quantitative confirmation of the way a rubber band goes very stiff just before it breaks. (and new balloons are very difficult to get started when you blow the up.

Even steel springs start to creep, though. The spring in an airgun will need replacing after a lot of use and people feel it's necessary to maintain the 12ft lbs that's the maximum allowed.
 
hmmm27 said:
Hang the rubber band from a hook next to a wall.
Hang a weight on the rubber band.
Mark the wall.
Wait.
In the first couple of hours (from original stretched length ~87 cm of 5 bands looped to make a chain) it stretched ~6 cm and after a few days another ~10 cm. It still bounced up and down nicely. What do we mean by "elasticity", exactly?
S6300451.JPG

(The next day it had broken.)
 
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There are no language police. Words like elasticity can mean whatever the author wants.
 
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anorlunda said:
There are no language police.
That’s not always what we observe on PF. 😉
 
  • #11
Keith_McClary said:
What do we mean by "elasticity", exactly?
That is not a simple question. If you really want to know more, you can search elastomer mechanical properties modulus creep. This hit is a good overall look at elasticity of rubber bands and other elastomers: https://apps.dtic.mil/dtic/tr/fulltext/u2/273880.pdf. It's a little old, but the information is still good. Figure 2.2.1 shows a simple model for the response of elastomers that gives an idea of why this is not a simple question.

If you really want to learn more, search elastomer material models. If you start to feel like you are trying to drink from a fire hose, you are.
 
  • #12
jrmichler said:
If you start to feel like you are trying to drink from a fire hose, you are.
pin48272.jpg
 
  • #13
jrmichler said:
That is not a simple question.
It's an example where teaching by numbers (which is all there's time for in school) can let people down when they want to move on. Those textbook graphs are very often just not enough.
 

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