We use products every day that we pour, brush, squeeze, or move around in other ways. Think about something as simple as ketchup. When we squeeze the bottle, we want it to be thin enough to pour easily, even through a small hole. But as soon as it lands on our hot dog, we want it to be thick enough to stay put, at least until it's in our mouth! There is a whole field of science about how liquids flow. It's called rheology (pronounced re- as in remember and -ology). Rheology helps companies develop household products that are easier to use, as well as oils and greases that help your family's car run better and start more easily on cold mornings.
 
 

Cool Stuff You Can Do 

Get an adult to help you with this, and do it over the kitchen sink or somewhere else where making a mess won't get you grounded for the rest of your life! Mix a half-cup of cornstarch with 5-6 tablespoons of water. Add a little more cornstarch or water to make a thick paste. Notice how hard it is to stir? But just tip the cup and you see it move. Dig some out with a spoon and put a blob of it in your hand. Now dig under one edge and see if you can quickly roll it into a ball. What happens when you stop rolling it with your hand? It stays as a ball as long as you keep it moving, but as soon as you stop moving it then it turns back to goop! If you want to get even with someone, just ask them if they want to play with your "ball" and then drop it in their hand. Watch their face as the "ball" turns into a gooey glob right before their eyes!

Cornstarch paste is an example of a fluid that gets thicker the faster you move it. Pretty strange, huh? Actually you've seen this before. Have you ever walked along the beach for a long distance? What part of the beach did you walk on? Maybe you noticed that when the sand is too wet, you sink. When the sand is too dry, you also sink. But there's a spot where the sand is just a little wet; and you can easily walk on that part of the beach because it's like our cornstarch paste - just the motion from your foot stepping on it is enough to turn it solid.