This article comes from the WeChat public account: Bring science home (ID: steamforkids) , author: seven Jun, head Figure from: vision China
Did you know that rubber bands can be used as refrigerators, do n’t believe it? You can pull the rubber band on the head of the female classmate to try it. If you stretch it first, it will get hot. If you retract it again, it will become cold.
Under the infrared imager, the temperature of the stretched rubber band increases and the temperature decreases when retracted.
You may not feel it with your fingers, but still feel it with your lips, the most sensitive part of the human body.
Sure enough, right? If your lips are numb, you can smell the stretched rubber band. Does it smell like that? That’s the smell of volatiles from the hot rubber band.
Okay, finish the rubber band, You can return it to the stunned female classmates.
What practical use does this principle have in addition to increasing the social distance with girls? An old man on an oil pipe began to use this principle to make a refrigerator, the raw materials are only rubber bands and wooden boards.
He first designed the gear that can stretch the rubber band, so it looks like this-
Each rubber band bypasses the middle disc to form an A-shaped binding, and the two ends of the rubber band are tied to adjacent gears. In this way, as the gear rotates, the rubber band tightens for a while and relaxes for a while. Image source: Applied Science
In order to allow air to circulate, two small fans are also installed on the shaft-
Half of the rubber band is stretched and half is tightened. The stretched end is hotter, so it is placed outside the refrigerator and tightly inside the refrigerator.
Uncle shook his hands a few times, under the infrared thermal imagerThe temperature difference between the inside and outside of the rubber band refrigerator is about 2 degrees Celsius, which is very powerful.
There is also a bald man who is more fierce and directly cools the beer with a rubber band.
The pimping machine made by this big brother can warm up by 10 degrees Celsius after stretching, and can drop by 10 degrees Celsius when retracted. So he used this machine to ice beer.
After a few strokes, the beer surface will drop from 14 degrees Celsius to 12 degrees Celsius.
Image Source: Joerg Sprave
Of course, the above principle can also be reversed, but the result is completely opposite. If the rubber band is heated, it will shrink, and it will grow longer when refrigerated.
So some people with big brains made “self” wheels with rubber bands. The spokes on this bicycle are replaced with stretched rubber bands. See, it rolls up on its own-
Image Source: Adam Micolich
Actually not, the rubber band shrinks after being heated by the heater, and the rubber band that has not been heated remains the same, so that the two sides are tight and loose, the tension is unbalanced, and the axle begins to rotate.
So, what exactly is this principle and why does the rubber band get hot when stretched? In fact, this phenomenon was discovered by a blind scientist 200 years ago.
In 1805, John Gough, a British scientist who lost his eyesight due to smallpox Rubbing his mouth, this is how he discovered the nature of rubber. About 50 years later, Joule conducted further research on rubber bands, so this phenomenon was later called the Gough-Joule effect (Gough-Joule effect) .
Gov-Joule effect of sausage balloons made of rubber under a thermal imager: it becomes hot when it is blown large, and it becomes cold when it is deflated. Image source: Chris Cramer
The principle of the Gough-Joule effect was not adopted by the German chemist Hermann Staudinger until the 1930s. (Herman Staudinger) Wait for someone to untie. Feynman, a naughty boy, was once fascinated by the nature of rubber.
Originally, when the rubber is still in place, the long molecules like the noodles are entangled with each other, but they are very quiet and dare not move. At this time, the rubber molecule is amorphous.
Rubber molecules in natural state (left) and rubber molecules in stretched state (right)
When the rubber is stretched, the rubber molecules begin to become ordered and begin to crystallize. The energy from amorphous to crystalline releases energy, which manifests itself as the restlessness of molecules. We knew in middle school that the more active the molecule, the higher the temperature, so the stretched rubber band is hotter.
In turn, when the rubber band returns from the stretched state to the natural state, the rubber molecules undergo a transition from crystal to amorphous. This process requires heat absorption from the environment, so the rebound rubber band is cool.
Later, a study published in the American Journal of Physics in 2013 found that the tension of the rubber band is related to its heating, and the more the rubber band is pulled, the more heat.
Obviously, rubber bands are contradictory to what we usually say about thermal expansion and contraction. Physically speaking, thermal expansion and contraction are said to have a positive thermal expansion coefficient, while rubber bands have a negative thermal expansion coefficient .
In addition to rubber bands, many substances have a negative coefficient of thermal expansion, such as water and polyethylene. The water will shrink and rise below 3.984 degrees Celsius, so the volume increases after the water freezes.
Because polyethylene also has a negative coefficient of thermal expansion, polyethylene garbage bags can also be used as light wheels that will keep rotating under the sun–
So what’s the use of a negative coefficient of thermal expansion?
When making precision instruments, materials with negative thermal expansion coefficient and positive thermal expansion coefficient are often mixed together to create a mixture with a thermal expansion coefficient of 0, so that you can be cold and hot.
If you have filled your teeth, your caries will be filled with a material with a carefully designed coefficient of thermal expansion. Imagine that if the material used for filling the teeth will expand and contract, or shrink and expand, then eating hot pot while drinking milk tea is the same as punishment. You can only drink things with the same body temperature, such as fresh body fluids. Therefore, the coefficient of thermal expansion of the dental filling material is close to the enamel and does not change significantly with temperature.
Some scientists are now seriously thinking about the feasibility of rubber band refrigeration, because the environmental problems caused by refrigerator refrigerant are really too serious. No, recently the largest ozone hole in the history caused by refrigerant gas has appeared over the Arctic, and the area has grown to three times that of Greenland.
NASA recently photographed the increasingly large ozone hole (blue) above the Arctic, which has recently grown to three times the size of Greenland.
In October 2019, an engineering scientist at Tianjin Nankai University published a study in Science. They found that the cooling effect of rubber bands is really good, and the cooling effect of twisting is better than that of pulling.
They took several elastic materials such as rubber band, nylon, polyethylene fishing line, and nickel-titanium alloy wire with shape memory, and then continuously wound them to form a super-spiral spiral spiral.
After this wave of operation, the strongest of several different fibers rose by 15 degrees Celsius, and also dropped by 15 degrees Celsius when untied.
The rubber band coated with thermochromic dye changes color with temperature when twisted and relaxed. Image source: (DOI) 10.1126 / science.aax6182
They also tested the cooling effect of these fibers, and found that their cooling efficiency is comparable to that of ordinary refrigerators. And after twisting these fibers, the cooling efficiency is only twice that of non-twisting.
Temperature change of the unspiring rubber band under the infrared thermal imager. Image source: (DOI) 10.1126 / science.aax6182
They also built a mini refrigerator as big as a ballpoint pen refill, using twisted nickel-titanium alloy wires for cooling. Within seconds, the water in the small refrigerator dropped by 7.7 degrees Celsius.
After watching this experiment, I finally understand why girls only wear elastic stockings in winter and it ’s not cold anymore. It ’s not that they are not afraid of cold. The original tight stockings are warmer than autumn pants.
This article comes from the WeChat public account: Take science home (ID: steamforkids) , < / span> author: seven Jun