What is oobleck?
Oobleck is a peculiar substance that exhibits qualities of both a solid and a liquid. Squeeze oobleck between your fist, and it creates a solid ball in your hand. Release your fist, however, and it will spill between your fingers like a liquid.
This is because Oobleck is a non-Newtonian fluid. Non-Newtonian fluids are known as such because they don't follow Newton's law of Viscosity - which states that the viscosity of a substance remains the same, independent of any force that is applied to it. Water, for example, is a Newtonian fluid that will exhibit the same constant liquid properties, regardless of the amount of force that it is subjected to.
Contrarily, the properties of non-Newtonian fluids can change between those of solids and liquids under different applications of force. Whip up a quick, easy batch of oobleck to see what we mean!
Fun fact: oobleck gets its quirky name from the Dr. Suess book ‘Bartholomew and the Oobleck’.
How to make Oobleck
All you need is:
- 1.5 - 2 cups cornstarch or white cornflour
- 1 cup water
- Food colouring (optional)
- Pour water into a bowl and add a few drops of food colouring if desired.
- Add in cornstarch by the spoonful and stir until combined.
To test if your oobleck is the right consistency, try out some of these little experiments that also show off the unique properties of non-Newtonian fluids.
- Pick the oobleck up out of the bowl by squeezing it in your hand to form a ball. Uncurl your fist and the oobleck should drip out of your hands like a liquid.
- Take a spoon (or any kitchen utensil) and quickly hit the surface of the oobleck. The spoon will bounce back, giving the appearance of oobleck having a hard surface. Press the spoon slowly against the oobleck, however, and it will sink instead.
- Try swirling your fingers or a utensil through the bowl of oobleck – slowly at first, then quickly. You will face far more resistance when trying to move quickly through the oobleck.
- Pro tip: to dispose of your oobleck, simply leave it out to dry, then crush it up and pop it into your compost.
How does it work?
Oobleck is, specifically, a shear thickening non-Newtonian fluid. This means that it thickens, or becomes more viscous or solid, when force is applied to it.
Applying quick pressure (such as hitting it or squeezing it) increases the oobleck's viscosity as it forces the cornstarch particles together rapidly. Releasing that pressure, or applying force slower, allows the cornstarch particles time to separate and move out of the way - making it behave like a liquid instead!
What are some other non-Newtonian fluids?
Oobleck is a fun experiment, but the fact is that we encounter non-Newtonian fluids all the time in everyday life.
Another example of a non-Newtonian fluid is ketchup (tomato sauce). Ketchup is a shear thinning non-Newtonian fluid that behaves in the opposite way to oobleck – it becomes runnier (less viscous) under pressure. This is why shaking or hitting a nearly empty bottle helps get the last remaining sauce out - the force applied makes the ketchup runnier. Once it's on your plate, however, it becomes much thicker so it doesn't run all over the place.
Body lotion is another shear thinning non-Newtonian fluid that becomes more fluid when force is applied, which is how it moves easily through pump bottles and over the skin, but thickens once applied so it doesn’t simply flow off your skin like water.
From peanut butter, to shampoo, and even paint; are there any other non-Newtonian fluids you can think of in your household?