Chewing gum can actually open coconuts. It's true that softness can overcome hardness!

Audit expert: Miao Guangyao

PhD in Condensed Matter Physics

Yesterday, when I was surfing the Internet, I saw a netizen cracking a coconut shell with chewing gum! As a coconut juice lover, I have bought many coconuts, but every time I either asked the store to help me crack the shell, or I cracked it myself.

It is hard to imagine how such a hard coconut shell can be "broken" by soft chewing gum. After careful investigation, the editor found out that chewing gum can really break the coconut shell!

Source: Baidu Encyclopedia

Non-Newtonian fluid

Before explaining why "chewing gum can crack coconut shells", we first need to understand a special substance - non-Newtonian fluid.

In physics, non-Newtonian fluid refers to a fluid that does not satisfy Newton's experimental law of viscosity and the nonlinear relationship between shear force and shear strain rate, and will exhibit the characteristics of a solid or liquid under different stress conditions.

Source | Sina News

There are many types of non-Newtonian fluids, which can be mainly divided into pure viscous non-Newtonian fluids and viscoelastic non-Newtonian fluids. This type of fluid includes various polymer solutions, foam solutions, suspensions, biological fluids, pastes, etc. For example, egg whites, chewing gum, blood, etc. in daily life all have the characteristics of non-Newtonian fluids.

In various daily experiments, the non-Newtonian fluids that people often use are usually two types of pure viscous non-Newtonian fluids, namely shear thickening fluids and shear thinning fluids . The chewing gum that is cracked into a coconut shell mentioned above is a shear thickening fluid, which we will talk about in detail below.

Shear thickening fluid, soft but not hard

Shear thickening refers to the phenomenon that when the shear rate or shear stress increases to a certain value, a new structure is formed in the liquid, causing an increase in resistance, resulting in an increase in the apparent viscosity of the liquid, accompanied by an expansion of volume.

In general, shear-thickening fluids appear to be thin and soft. When subjected to external shear forces, such as violent stimulation such as impact, the intermolecular stress inside the fluid will increase, which will manifest externally as increased viscosity and a hard texture. This is commonly known as becoming stronger when faced with stronger forces and being soft but not hard.

Source | Baidu Knows

Source | Internet

Source | tumblr.com

The reason why chewing gum can break open the coconut shell is because the gum base contained in the chewing gum belongs to this kind of shear thickening fluid; if you press the chewing gum gently, you will feel that it is very sticky and soft, but if you hit it quickly, the chewing gum will harden instantly. Coupled with the reaction force caused by the impact when you hit the coconut down hard, it is not surprising that it can pierce the coconut shell in minutes.

Source | Screenshot of the variety show "Come on! Towards the Future"

In daily life, we can also easily make a shear thickening fluid, such as water starch formed by mixing corn starch and water.

If you stir with a spoon, you will find that as the stirring speed increases, the difficulty of stirring also increases; if you poke the surface of the water starch with a spoon quickly and forcefully, it will not move; but if you put the spoon on it, it will slowly sink~

Shear thickening fluids have a wide range of practical applications. In the field of scientific research, liquid bulletproof vests have been made using the properties of this fluid. They are more comfortable to wear and have better bulletproof effects than ordinary fiber bulletproof vests.

Shear-thinning fluid, hard to hard, not soft

In contrast to shear-thickening fluids, shear-thinning fluids (shear thinning) refer to fluids whose viscosity decreases with increasing shear strain rate, that is, they become weaker when exposed to strong forces and do not absorb softness but hardness.

Source | Baidu Knows

Generally speaking, when there is no shear force, they are in a viscous state. If a sufficiently large shear force is applied, such as rapid stirring, the molecular chains in the fluid will slide more easily against each other and the fluid will become thinner.

For example, ketchup is also a shear-thinning fluid. When a ketchup bottle is empty, there is often a layer of ketchup at the bottom, which cannot flow out if it is gently turned upside down. However, when we knock the bottom of the bottle or shake the bottle vigorously, the ketchup will flow out.

Source | soogif.com

Swamps are also shear-thinning fluids. If you struggle quickly when you are trapped in a swamp, it will cause the swamp to thin out, and then accelerate the sinking. So we see some survival guides telling you that once you are trapped in a swamp, don't struggle hard but try to spread your limbs to slow down the sinking speed. If you really encounter danger in a wild swamp, remember not to struggle recklessly.

Why chewed gum loses its "magic power"

Back to the question of "chewing gum breaking open the coconut shell", if it is chewed gum, can it also break open the coconut shell?

This question starts with the composition of chewing gum. The main components of chewing gum are sugar and ester gum matrix. In chewed gum, the sugar is absorbed by the human body, the sugar content becomes less and the water content becomes more, which causes its structure to change and its non-Newtonian fluid properties disappear.

Compared with unchewed gum, chewed gum has poor shear thickening effect, so it naturally loses its "magic power", and the effect of smashing coconut shells will also be discounted.

By the way, if you want to try "smashing the coconut shell with gum" after reading this article, I would like to give it a try. First, the gum should be kneaded into a cone shape, preferably a larger one. Second, you should smash the coconut shell steadily and accurately, so that the chances of success are higher. And the most important point is: you must smash the coconut shell in a solid and reliable container! Otherwise, although the shell is successfully broken after smashing, all the coconut juice inside will flow out!