Toothpaste is one of the daily necessities that we are very familiar with, because we brush our teeth every day and squeeze toothpaste every day.
Speaking of squeezing toothpaste, have you ever wondered why toothpaste must be squeezed to come out, why can't it be poured out?
Also, we may not even know more about this extremely common item, for example, is toothpaste liquid or solid?
The existing knowledge of the form of matter allows us to easily tell which things are liquid, which are gas or solid, but there seems to be no suitable description for toothpaste.
So, what exactly is toothpaste?
toothpaste was originally a non-Newtonian fluid
toothpaste is a non-Newtonian fluid, more specifically it should be a Bingham fluid, which is one of non-Newtonian fluids.
Non-Newtonian fluid in Physics is defined as a fluid that does not satisfy Newton's experimental law of viscosity, that is, a fluid whose shear stress and shear strain rate are not linear.
And we can simply understand that a non-Newtonian fluid is a fluid that "eats soft but not hard". The faster you are, the harder it will be, and when you slow down, it will behave very softly.
Although no one can do it in water, this martial arts skill is completely achievable in non-Newtonian fluids.
Most biological fluids, that is, fluids in organisms are non-Newtonian fluids, such as blood, lymph, and cytoplasm.
The oil, paint, soy milk, egg whites, melted chocolate and dough that we know are all non-Newtonian fluids. Friends who have kneaded dough should have a deep understanding.
Bingham fluid is also called Bingham plastic fluid or Bingham plastic,It is a special non-Newtonian fluid. Common examples in life are toothpaste and paint.
It is special in that it will only start to flow when the force it receives reaches a certain critical value. Below this critical value, it is an ordinary elastomer.
Is this description completely consistent with our usual experience of squeezing toothpaste!
Some toothpastes are easy to squeeze out, while others are more strenuous. This is because different toothpastes have different critical values of force required.
Of course, basically all toothpaste has a lower gravity than its critical value, which is why the toothpaste does not flow out.
By the same token, the paint applied to the surface of the object will not flow down easily. So we have to spread it evenly with a brush.
Why don’t the colors of the color bar toothpaste mix?
The different colors of the color bar toothpaste are poured in in different proportions during production. Even if the toothpaste is extruded, the positions of the different colors are still neat and tidy.
As mentioned above, the basic characteristic of Bingham fluid is that it flows when subjected to force, and is ordinary elastic when not subjected to force. When it is stationary, that is, when the toothpaste is not squeezed, the toothpaste exhibits ordinary elasticity. This state is actually more like a solid, so different colors will not mix basically.
Moreover, in order to prevent different colors from infiltrating each other, the manufacturer also added a polymer agent to the toothpaste, so that the toothpaste is more difficult to mix.
The color of the static toothpaste does not mix. It is easy to understand, why the different colors of the extruded toothpaste still do not mix?
This is actually related to fluid flow.
The flow of fluid generally has two forms of laminar flow and turbulent flow. Literally, the former is "layered flow" and the latter is "turbulent flow".
The process of toothpaste being squeezed out by us belongs to laminar flow,Because there are levels of flow, all parts of it are still in their place and neatly.
Laminar flow and turbulent flow are both concepts in fluid mechanics . How to distinguish the flow of a liquid from laminar flow or turbulent flow?
This will use Reynolds number .
Reynolds number is the ratio of the inertial force of the fluid to the viscous force. When the ratio is small, it means that the viscous force has a greater influence than the inertial force. On the contrary, it means that the inertial force has a greater influence than the viscous force.
In the former case, the fluid flow is stable and presents laminar flow. In the latter case, the fluid flow is unstable and presents turbulent flow.
For the fluid in the pipeline, the flow with Reynolds number less than 2300 is laminar flow, the Reynolds number is equal to 2300～4000 is a transitional state, and the Reynolds number is greater than 4000 is turbulent flow.
The process of toothpaste being squeezed out is equivalent to flowing in a pipe. We can infer that the Reynolds number of toothpaste is less than 2300.
Is the non-Newtonian fluid solid or liquid?
Since toothpaste is a non-Newtonian fluid, then we ask whether the non-Newtonian fluid is liquid or solid, which is more meaningful than whether the toothpaste is solid or liquid.
Whether a non-Newtonian fluid is a solid or a liquid, the question is like whether a liquid crystal is a solid or a liquid. There is no clear conclusion at present.
It is generally believed that non-Newtonian fluid is a state between liquid and solid, neither liquid nor solid.
As more and more states of matter are discovered, the three basic forms of gas, liquid and solid of ordinary matter certainly cannot cover all matter.
Finally
Squeezing toothpaste is a common thing, but now you know, why only through squeezing,Toothpaste will come out of the toothpaste tube, and I also know why different toothpastes require different force to squeeze out.
Do you suddenly feel that squeezing toothpaste is also meaningful?
Of course, don't procrastinate like "squeezing toothpaste", it will be complained.
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