Making an ideal sauce. There's number of factor we need to consider. The first one is it has to be easy to be poured out from the container. Secondly, once it's been poured out, especially pour onto our food, those food, that means the sauce can still able to cover the whole food. And finally, once it can be covered the food, and all the sauce will actually run over the plate. So these are the m, three major factor we have to consider when we try to prepare our sauce. So you wonder any liquid can have these properties. So in fact of the physical property of an ideal sauce, that is, if we can actually do these three things. Firstly, it has be a low viscosity when we try to pour out from a container; so that it's be easy to pour out. But however once is being poured out on the food basically. In order to stop it for one all over the plate the viscosity has to he increased after is being poured out from the container. Now, if we look at that by the, the physics, really classical physics, many kind of fluid, in fact, they are served as a Newtonian fluid. You wonder what's the meaning of Newtonian fluid. Newtonian fluid means the viscosity, it doesn't change, even though there is any pressure change. Like for example, we have a bottle water. So if we tried to apply certain pressure onto the water, it flow at a certain rate. But however, when we increase the pressure, what you can see, the flow rate will also increase. So that actually refer to when we have pressure change, the flow rate also change. But in fact, the viscosity, it is more or less stayed constant. So, this is so-called the classical, so-called a Newtonian fluid. But however, there's always exception in science. We have not only Newtonian fluid, we have Non-Newtonian fluid. So what is so-called a Non-Newtonian fluid? Instead of a constant viscosity with change in the pressure, we have two type of Non Newtonian fluid. One is so called a shear thinning. That is, if the viscosity just try to decrease when we exert pressure. Or in other words, if the food, if we don't exert any pressure on it, the viscosity more or less, remain at a high value. But, if we try to increase the pressure, the viscosity sudden drops, right. So, in our daily life, which type of food, referring to so-called shear thinning so, Zoe. I've one very good example. One of the example is so-called ketchup, here. So, when Zoe is try to open up bottle ketchup and we try to tip it up, it won't, it, the ketchup won't, won't flow out from a container. But however, when a slight pressure add on to it, it suddenly flow. So this actually demonstrate so-called, a shear thinning example. So that means before, it actually tip up the bottle because the pressure is not large enough. To change the viscosity so that those ketchup will still remain in the container. But when Zoe just tried to apply more pressure onto it, the viscosity of the ketchup suddenly decreased. So you can see all the ketchup immediately suddenly run out from the container. Apart from the shear thinning I just demonstrate, the opposite of shear thinning is so-called the shear thickening. Now I'm going to also demonstrate what is so-called shear thickening. So here we have cornstarch and we have water. So when we just try to add the two things together, It form a something like a suspension. And this special suspension has an interesting property of so called shear thickening. As I just mentioned, shear thickening in fact is opposite of shear thinning. So that means it act oppositely. Basically, when we try to apply pressure on to it, the viscosity suddenly increase. It just try the opposite, the extra pressure we have. On the contrary, when we try to do it at a slow, so-called pressure, the viscosity in fact is really small. So, Zoe had and so, we prepared a small bowl of this corn starch suspension. Right now we have a larger bottle of suspend, of corn starch suspension. What we want to demonstrate is try to apply large pressure. So you see she can get her hands get into the suspension. But, however, when she was trying to do it in the slow way, she can able to immerse all his finger into a suspension. So you can see. So this is exactly how sheer thickening behave.