Non-Newtonian fluid
Don’t punch it—it fights back!
Safety
- Carefully review the general safety advice on the back of the box cover before starting the experiment.
- Never eat or drink any of the substances provided. Do not use for culinary purposes.
- Perform the experiment on the safety tray and use protective gloves to avoid staining your hands.
Disposal
- Pour liquids down the sink. Wash with an excess of water.
- Dispose of solid waste together with household garbage.
Scientific description
You may already be familiar with a property of liquids known as viscosity—the ability of a liquid to resist external influences, such as being stirred with a spoon or poured into another glass. Everything, including liquids, consists of tiny particles (molecules) that come in different sizes. As you stir a liquid, the spoon shifts some molecules, which push the molecules closest to them, which push the next closest ones, and so on. The easier it is for the molecules to move out of the way of the spoon, the lower the viscosity of the liquid.
If the viscosity of a fluid increases accordingly with the rate of mixing, such a fluid is called a Newtonian fluid, after the scientist Isaac Newton. Fluids in which the viscosity drastically depends on the rate of interaction are called non-Newtonian fluids.
The non-Newtonian fluid that you’ve made consists of starch 
and water 
. Large starch molecules interact with each other and form clots . If a stirring rod is slowly lowered into the fluid, the clots have time to disperse, and the water molecules help them move 
. When struck sharply, the clots , unlike the water molecules , do not have time to move away. Therefore, in the area of impact, they cling to each other and form a solid structure that does not allow the stirring rod through.
