The Mystery Substance Lab

1. The Mystery Substance Lab Learning targets for this lab Students can describe a Non-Newtonian fluid. Students can describe how this substance changes viscosity with pressure. Students can use terms related to the viscosity of materials.

2. Some examples of non-Newtonian fluid • A Newtonian fluid has a linear relationship between force and its resistance • Non-Newtonian fluid does not have a linear relationship between force and resistance to that force. • Thixotropic gets more liquidly with force • Dilatant gets more vicious (thicker) with force

4. Mystery Substance A Lab goals: Students can describe what a non Newtonian fluid is. Students can describe how this substance changes with pressure. Students can describe thixotropic and dilatent. Ideas for hypothesizes: (these are not hypothesis yet.) How would it act under vibration? How would different temperature objects affect the substance? How would different shape objects affect the substance? Does this substance show thixotropic or dilatent behavior? Propose a new hypothesis to the instructor for approval. Materials Needed: Cups Mystery substance Water Safety Precautions: Don’t eat the substance Keep your area clean Not part of the lab but fun to try: Quickly poke substance with your finger then slowly push finger into material Pour into hand and roll into a ball Go outside and toss to a friend. See how far apart you can get. Experimental procedure: Cover work area with a piece of paper. 1. Mix material until it is a thick liquid 2. Depending on your hypothesis you should do some of the below procedures. 3. Take material to the caster or other vibrating surface 4. Place a ball of it and see how long it take to flatten (time it with clock) 5. Take same size ball and see how long it takes with the vibration off. 6. or Time how long it takes to make a circuit of the cup with your finger when you are pushing hard, then time it when you are not pushing hard. 7. or Time how long it takes for a warm object to circle the inside of you cup (your finger) then time how long it takes for a cool object (a pencil) to do the same. Questions 1. In your own words explain how this material is able to change from a solid to a liquid and back with only pressure? 2. Please list 2 factors that would limit how far you could throw a ball of this material. 3. Please describe the types of non-Newtonian fluids

5. How does it change from liquid to solid? • What do you think? • Discuss with your neighbors. • Be prepared to share out your hypothesis.

6. What just happened? Two ways to explain the behavior • When you add force the molecules stack up when there is no force they pop apart.   • A cornstarch/water slurry is a suspension of a solid in a liquid. At a certain ratio of cornstarch to water, the critical concentration is reached. Exactly at this point there are no voids or holes. The starch particles are in contact with each other and the water fills the interstitial space. At this point, it cannot be said if you have a 'solid' or a 'liquid' the application of pressure changes that and the flow characteristics change. The water is 'squeezed out' [into adjacent areas]leaving the starch behind as a damp solid. This is the same phenomenon that you see when walking along wet sand at the beach: your footsteps look dry behind you, even though they were made in wet sand.

7. Applications and other cool stuff • Cornstarch monster • “Walking” on “water” • Liquid armor • Liquid armor in hats