You’ve probably heard of Oobleck, a mix of cornstarch and water. It’s a fluid that is soft when less force is applied but hard when more force is applied; this is because Oobleck is a non-Newtonian fluid.
In this blog post, we’ll learn more about what non-Newtonian fluids are, discussing the science behind their unusual behaviour, and why they are both a staple in school science experiments and a subject of cutting-edge research in engineering and medicine.
Differences Between Newtonian & Non-Newtonian Fluids
Most of the fluids we encounter daily—such as water, milk, and even engine oil—are classified as Newtonian fluids. In these substances, the viscosity (a measure of a fluid’s resistance to flow) remains constant regardless of the force applied – it doesn’t matter if you pour water slowly or in a rush, its flow always remains consistent.
Non-Newtonian fluids, however, defy this rule. Their viscosity changes when a force (or stress) is applied. This means that under different conditions, the same fluid can behave like a liquid or like a solid. The classic example of this is, Oobleck. When you apply a sudden force to Oobleck—say, by punching it—it behaves like a solid. But when you allow it to sit undisturbed or stir it slowly, it flows like a liquid.
The Science Behind Non-Newtonian Behaviour – Molecular Interactions
At the heart of non-Newtonian behaviour is the way particles interact within the fluid. In a mixture like Oobleck, small cornstarch particles are suspended in water. Under slow or minimal stress, these particles have enough time to move past one another, allowing the fluid to flow smoothly. However, when a sudden force is applied, the particles have no time to rearrange. They momentarily “jam” together, creating a temporary structure that resists flow—much like a solid.
Types of Non-Newtonian Fluids
Non-Newtonian fluids are not all the same; they can be broadly categorised into two main types:
Shear-Thickening Fluids –
These fluids become more viscous (thicker) when subjected to a rapid force. Oobleck is the most famous example. The quick force prevents the particles from moving aside, causing them to lock together and create a temporary solid-like state.
Shear-Thinning Fluids –
In contrast, these fluids become less viscous (thinner) when agitated or stirred. Ketchup is a well-known example: you may have noticed that a bottle of ketchup often requires a good shake or tap to get the condiment flowing smoothly out of the bottle.
A Hands-On Experiment
Oobleck is perhaps the simplest and most accessible non-Newtonian fluid you can experiment with at home or in a classroom. Here’s a detailed guide to making your own Oobleck:
Materials Needed:
- Cornstarch (about 2 cups)
- Water (roughly 1 cup)
- A large mixing bowl
- Food colouring (optional, for fun visual effects)
Method:
- Combine Ingredients
Start by pouring the cornstarch into the bowl. If you’d like to add a bit of colour, mix in a few drops of food colouring with the water. - Mix Slowly
Gradually add the water to the cornstarch, stirring continuously. You might need to adjust the ratios slightly—if the mixture is too runny, add a bit more cornstarch; if it’s too stiff, add a little more water. - Test the Consistency
Once mixed, experiment with the fluid:- Slow Motion – Dip your hand into the mixture slowly. Notice how it flows around your fingers like a liquid.
- Quick Motion – Try tapping or squeezing the mixture quickly. You should feel it harden under sudden pressure.
Real-World Applications and Relevance
Non-Newtonian fluids are more than just a science fair curiosity; they have practical applications across various fields.
Impact-Resistant Materials
Many protective materials and body armours utilise non-Newtonian fluids. These materials remain flexible during normal movements but harden upon sudden impact, providing extra protection. For instance, some sports equipment and automotive components incorporate non-Newtonian compounds to absorb shock and reduce injury.
Industrial and Manufacturing Uses
Non-Newtonian fluids also assist in many industrial processes. In the field of printing, for example, certain inks are designed to change viscosity under pressure, ensuring that they spread evenly and maintain high quality in various printing techniques.
Biomedical Engineering
Recent advances in biomedical engineering have begun to explore non-Newtonian fluids for applications such as drug delivery systems and prosthetic devices. Their unique properties can help in designing systems that respond dynamically to the body’s movements and stress levels.
Historical Perspectives
The discovery of non-Newtonian fluids happened long after Sir Isaac Newton formulated his laws of motion and viscosity in the 17th century, which focused on fluids with constant viscosity. In the 19th century, scientists started noticing that some substances—such as suspensions and colloids—behaved differently under varying forces, hinting at the complex behaviour that would later be classified as non-Newtonian.
By the 20th century, with advances in experimental techniques and mathematical modelling, researchers began to systematically study fluids like ketchup, toothpaste, and the now-famous Oobleck. These studies led to the categorisation of non-Newtonian fluids into types such as shear-thickening and shear-thinning. This period marked a turning point, as understanding the molecular interactions behind these unusual behaviours not only triggered further academic research but also created opportunities for practical applications in industries ranging from protective gear to innovative manufacturing processes.
Summary
This blog post discussed what non-Newtonian liquids are and how they work, as well as practical uses, their discovery and how you can experiment with them at home. Thanks for reading!
– Written by Hamd Waseem
