You take a pristine-looking Oreo from a package of seemingly identical sandwich cookies, and you decide to open it up to eat the creme filling first. You gently twist the cookie apart without breaking the chocolate wafers, but the creme sticks to one side only. Why? Happily, the physics of fluids helped two MIT students solve this delicious mystery. Read on to find out what they learned, and how you can test their results at home.
The term may be unfamiliar, but we all have a sense for viscosity. We often think of it colloquially as the “thickness” of a fluid. It’s the property that makes honey pour so differently from water. Fluid dynamicists – scientists and engineers who study how liquids and gases move – tend to think of viscosity in terms of a fluid’s resistance to flowing or changing its shape.
Why do so many fluids behave counterintuitively? Many substances in our lives – like oobleck, slime, or Silly Putty – don’t quite behave the way we expect a fluid to, despite some fluid-like properties. These substances fall into a special category: non-Newtonian fluids. Scientifically, this term is a bit of a catch-all for any substances that have a complicated relationship between their apparent viscosity and the force applied to them.
Surface tension is a somewhat peculiar force. Its effects are all around us, from bubbles and droplets to cleaning our dishes. Surface tension is an important force in our daily lives. But what is it really? Since it tends to act at the scale of millimeters or smaller, we don’t always notice it. It’s critical, however, for many creatures smaller than us, from water-walking insects to star-nosed moles that sniff out food underwater. So what is surface tension and where does it come from?
For the past two decades, giant bubble enthusiasts have been creating soap film bubbles of ever-increasing volumes. As of 2020, the world record for a free-floating soap bubble stands at 96.27 cubic meters, a volume equal to about 25,000 U.S. gallons! For a spherical bubble, this corresponds to a diameter of more than 18 feet and a surface area of over 1,000 square feet. How are such large films created and how do they remain stable? What is the secret to giant bubble juice? Click to find out more!