Non-Newtonian fluid: DIY

When adjacent layers of particles (molecules) in a fluid move relative to each other, they collide, due to which the velocities in different layers equalize, and the energy of any external action is transferred in space. In such cases, one speaks of the forces of internal friction, or viscous friction. The relationship between viscous friction and the relative velocity of the layers is called dynamic viscosity. In most liquids we know, viscosity is little dependent on the nature of the external action. Their motion is described by Newton's laws, and the liquids themselves are called Newtonian. These include water and aqueous solutions, alcohol, gasoline and petroleum products.

Power in this experiment matters. In order for a real show to play out on the speaker diffuser, enough starch suspension must be given enough energy. Everything is as always: the larger the diameter of the speaker and the more watts the amplifier gives out on the mountain, the sooner the hero of the day will dance.

However, there are non-Newtonian fluids, the viscosity of which is largely determined by the nature of the external action. Try stirring some starch in water. "Try" here is a very important word. Out of habit, putting a lot of effort into this process, you will soon feel that the spoon is stuck in suspension, like in a frozen cement. Do not give up or dilute with additional water. Just slow down, and you will suddenly find that the spoon passes freely through the suspension, like through water. Try to hit the liquid with your fist and sharply pull your hand back - the skin will not even get wet. And if you mix a whole bath of such a mass, you can dance on it. But if you slow down the dance for a second - and you go to the bottom. So that!

Food colors can add color to the experience. Handling an obstinate suspension by hand is a thankless task. But dyes, and if desired also starch and water, can be added directly to the vibrating dynamics. Slow mixing of paints creates a very spectacular effect. Non-Newtonian fluid can be purchased at the store. The toy is called Handgum, or chewing gum for hands.

To put the experience to the speaker, as a low-frequency generator (our choice is 30 Hz), we used an Android mobile phone with the corresponding application. If you want to save the speaker, cover it with cling film - this will not affect the result of the experiment.

The article “But Newton Was Not Invited” was published in the journal Popular Mechanics (No. 5, May 2012).