# Rubber Bands and Heating: Does Weight Go Up or Down?

• daniel_i_l
In summary: So, in summary, the weight hanging from a rubber band will actually go up when the rubber band is heated. This is because the heat causes the rubber band to contract, creating more tension and pulling the weight upwards. This may seem counterintuitive, as we are often taught that heating causes expansion, but it is not always the case. In some materials, such as ice, heating can actually cause contraction. For rubber bands, the composition and properties of the band will also play a role in how it reacts to heat.
daniel_i_l
Gold Member
Suppose you have a weight hanging from a rubber band and you heat up the rubber band, will the weight go up or down? from grade-school the answer "down" was pounded into my head - obviously - when something is heated it expands! but yesterday i was reading the Feynman lectures and in the chapter about statistical mechanics he said that the rubberband actually gets shorter when heated. he explained that heating the RB gives it more tension and so it pulls harder on the weight and the weight goes up. but isn't it true that as something is heated it expands?
Thanks.

isn't it true that as something is heated it expands?
Not universally. A more common example is ice: heating ice will cause it to shrink. And the water you get will continue to shrink as heated, until about 4° celsius.

Heating something causes its molecules to become more energetic. More energetic particles tend to remain further apart than less energetic particles (thus expanding the object), but sometimes other considerations predominate.

For basic ice, it's because water molecules tend to organize into a sparse crystalline structure. When heated, the crystal dissolves and the molecules arrange themselves in a more random (and thus denser) fashion.

I don't know what's going on for a stretched rubber band. My first guess is that it wants to expand laterally, which makes the rubber band feel more stretched, and thus it tugs harder. I have no reason to believe that's right, though.

I guess that it would depend upon the composition of the band. Generally, I would expect it to stretch farther since rubber softens when heated. (Don't ask me how I know this; let's just put it off as a bad experience...)

Danger said:
I guess that it would depend upon the composition of the band. Generally, I would expect it to stretch farther since rubber softens when heated.
Not for small increases in temperature (Le Chatelier). For most common types of rubber (polyisoprene based) the typical deflection temperatures or maximum working temperatures are from about 50C to about 250C, so it would take some serious heating to get the rubber to soften to its yield point.

PS: Some related discussion here: https://www.physicsforums.com/showthread.php?p=419641#post419641

Last edited:
Hmmm... interesting.

## 1. Does heating a rubber band affect its weight?

Yes, heating a rubber band can affect its weight. When a rubber band is heated, it expands due to the increased molecular motion. This expansion can result in an increase in weight.

## 2. Does the weight of a rubber band go up or down when heated?

The weight of a rubber band can go either up or down when heated, depending on the type of rubber band and the temperature to which it is heated. Some rubber bands may become heavier due to the expansion of the rubber, while others may become lighter if the heat causes some of the molecules to break down and evaporate.

## 3. Can heating a rubber band change its physical properties?

Yes, heating a rubber band can change its physical properties. The increased molecular motion can cause the rubber band to become more pliable and stretchy, while also making it more susceptible to breaking or melting.

## 4. Is it safe to heat a rubber band?

Heating a rubber band can be dangerous, as it can release harmful fumes if heated at high temperatures. It is important to follow safety precautions and use proper equipment when heating rubber bands.

## 5. How does heating a rubber band affect its elasticity?

Heating a rubber band can decrease its elasticity, as the heat can cause the rubber molecules to break down and lose their ability to stretch and return to their original shape. This can make the rubber band more brittle and prone to breaking.

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