In this Rosie Labs guide you will find:
- Productive struggle opportunities for students during their project build,
- Lesson objectives and concept overview,
- Optional STEM topic video to share with participants,
- Step-by-step instructions and video of the Rosie Riveters’ Slime project,
- Optional STEM activities to further explore the objectives and concepts used in the project build.
Objective
To understand what a polymer is and how chemical reactions can change the state of materials by making slime!
Concept Overview and Experiment Inspiration
There are three states of matter: solid, liquid, and gas. Solid has a definite shape and doesn’t change its form, like a pencil. Liquid has no definite shape but takes the shape of its container, like water. Gas has no definite shape or volume, like air. Slime is a fun example of a material that can change its state. When you first make slime, it starts as a liquid. But as you play with it, the slime will become more solid-like and then return to a liquid form. This is because the slime is a type of non-Newtonian fluid, which means that it acts differently than regular liquids and can change its form based on the force applied to it.
Non-Newtonian fluids are special types of liquids that do not follow the rules of regular liquids. Regular liquids, like water, always act the same way and their behavior can be predicted by Sir Isaac Newton’s laws. But non-Newtonian fluids are different, they change their behavior depending on how much force is applied to them. For example, if you hit a non-Newtonian fluid like slime lightly, it will feel like a liquid and will flow easily. But if you squeeze it hard, it will feel more solid, like a gel. That’s why slime can change from a liquid to a solid and back again depending on how you play with it. Cool, right?
Have you ever wondered why some fluids move fast and some move slow? How quickly fluids flow is known as their viscosity. It’s kind of like thinking about how thick a liquid is. A liquid that moves fast is known as non-viscous, while a liquid that moves slowly is described as viscous.
Normally, viscosity changes with temperature. A fluid that is warmed up becomes less viscous (flows quicker) and a fluid that is cooled down becomes more viscous (flows slower). Fluids that change viscosity based on temperature are known as Newtonian fluids. That is because it does not matter how much you play with them; their viscosity will only change when the temperature changes. Water and oil are great examples of Newtonian fluids that stay the same even when physically moved.
However, there are some fluids that do not follow Newton’s idea of viscosity. They can exhibit properties of both a solid and a liquid depending on how they are moved. These fluids are non-Newtonian fluids and their viscosity changes based on something called shear stress. Shear stress (or pressure) is caused by physical movement including squeezing, stirring, agitating, or applying any type of physical pressure on the surface of a fluid.
Some great examples of non-Newtonian fluids are quicksand, ketchup, and slime. Just like in the movies the more you move when trapped in quicksand the faster you sink! That is because you are applying shear stress to a non-Newtonian fluid, which changes its viscosity. The same goes for ketchup in a bottle. You sometimes need to hit the ketchup bottle hard to get things moving.
Slime is like quicksand, a non-Newtonian fluid, but instead of becoming less viscous when it is moved, it becomes more viscous! How exactly does this work in slime? Well, most types of slime and non-Newtonian fluids are examples of polymers. A polymer is a very large chain of molecules made up of repeating groups of smaller molecules known as monomers. Polymers are extremely flexible and can link together to take the shape of any container. In slime, glue is our polymer, and it gets linked together with the addition of baking soda and boric acid (contact solution). The baking soda and boric acid work to create a web of glue polymers that are stronger and denser but are still flexible. Shear stress is then able to make the polymers stiffer or more loose creating what we know as non-Newtonian fluids.
Science Goals
- How quickly fluids flow is known as their viscosity. A liquid that moves fast is known as non-viscous, while a liquid that moves slowly is described as viscous.
- Fluids that change viscosity based on temperature are known as Newtonian fluids. Water and oil are great examples of Newtonian fluids that stay the same even when physically moved.
- Non-Newtonian fluids change in viscosity from shear stress, which is physical movement including squeezing, stirring, agitating, or applying any type of physical pressure on the surface of a fluid.
- A polymer is a very large chain of molecules made up of repeating groups of smaller molecules known as monomers. Polymers are extremely flexible and can link together to take the shape of any container.
- In slime, glue is the polymer, and it gets linked together with the addition of baking soda and contact solution. The baking soda and contact solution work to create a web of glue polymers that are stronger and denser but are still flexible.
- Shear stress, or the physical movement of the products, make the polymers stiffer or more loose creating what we know as non-Newtonian fluids.
Vocabulary
- viscosity– the property of a liquid that describes how fast or slowly it will flow.
- polymer– a very large chain of molecules made up of repeating groups of smaller molecules known as monomers. Polymers are extremely flexible and can link together to take the shape of any container.
- shear stress: the pressure caused by physical movement including squeezing, stirring, agitating, or applying any type of physical pressure on the surface of a fluid that changes the viscosity of the fluid.