App Description: If you have questions about the properties of liquids ‘floating’ through your head then this is the app for you. Although this app addresses questions related to states of matter, the visuals in the app are more related to fluid dynamics. The app is pretty simple to use. The main visual is of particles that flow and swirl if you tilt the iPad screen or if you use your fingers to manipulate them. On the right hand corner is an ‘I’ button that opens up a list of functions whose values can be changed to alter the state of the particles. The functions listed in the app are density, stiffness, elasticity, viscosity, yield-rate, gravity and smoothing. Each of their values can be played around with to see how the liquid changes – for example by reducing density, the liquid particles disintegrate all over the place and the particles mimic gas molecules instead of looking like a swirling liquid. If you increase the density, the particles come together making the visual look like a thick liquid.

How We Use It: We have a Viscosity tester exhibit in the Matter Factory at the Children’s Museum of Houston. The tester has 3 different cylinders of liquids of varying thickness. The kids can test the thickness by turning the steering wheel to check which one is the hardest to turn. The thicker the liquid, the harder it is to turn the wheel. In addition the kids can test the flow of different liquids by flipping three other cylinders and observing how quickly the balls flow through each of the liquids. This exhibit mostly teaches about the resistance of flow in certain liquids that have higher viscosity and density.

Our audience for iPad interactions at the museum is kids around the age 5 to 9 years. So they may not necessarily understand concepts such as viscosity, density and stiffness. Therefore our facilitators talk about the exhibit in terms of thickness of a liquid and how it resists flowing. The exhibit also has pictures of substances such as water, ketchup and peanut butter to reinforce concepts of how different liquids don’t flow in the same manner. The facilitators start off by observing what the child is doing. He would be turning the wheels and playing with the rotating cylinders. Some questions that the facilitators ask and discuss are –

• Then ask which wheel is harder to turn? Which ball travels faster in the tube?
• They talk about how one liquid (‘gooey stuff’ as some kids may call it) is thicker than the other which makes it harder to turn the wheel and for the ball to fall down.
• What makes peanut butter thicker than maple syrup? And maple syrup thicker than water?
• Can you pour water out of a bottle more easily than ketchup out of the bottle?

Then the facilitators use the app to mimic those real examples. They challenge the kids to play with the settings to make the fluid look like peanut butter or syrup or like the liquid in the cylinders.

Important note: With older kids, it is easier to talk about concepts such as viscosity and density. Our facilitators ask challenging questions such as – What happens when you heat peanut butter? It becomes less thick, why? This app is a good way to reinforce those concepts and talk about how heat changes the state of substances. It is an effective visual to show how thickness or thinness of a fluid affects its flow.