Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.
Physics is a daunting topic for many, with all the math and theories behind it making it seem rather inaccessible. Perhaps if we were to try and bridge it with things we are used to then that could help people understand and perhaps even appreciate it. With that in mind, lets look at some “everyday” events and see the interesting physics involved with them.
Yes, we are starting with wrinkles because often our day starts being surrounded by them in our bed. But nature is full of them, and they are difficult to describe how they form. But research from MIT may have some insight. They were able to create a mathematical formula that shows how wrinkles develop on round surfaces, as opposed to flat ones.
If we have different density layers with a hard one on top followed by a softer one below, then as material from below changes (like if air is sucked out, dehydration occurs, or saturation is reached) then the inflexible outer layer starts to compact in a regular pattern before devolving into a seemingly random assortment that depends on the curvature of the given moment. In fact, a model that takes into account the materials and curvature was developed that could someday give rise to choosing a design we desire (Gwynne).
Now onto food. Take a single piece of spaghetti, hold it at both ends, and try to break it exactly in half. Difficult, no? It wasn’t until 2005 when Ronald Heisser (Cornell University) and Vishal Patil (MIT) cracked the code. You see, no piece of spaghetti is truly straight. Instead, they have a small curvature to them and when we apply stress to the noodle it will break where that curvature is greatest. The resulting oscillations stemming from the break can cause further ones as the noodle loses structural integrity. But when the noodles were tested in a temperature and humidity controlled environment, scientists found that if we twist the noodle instead a full 360 degrees and then bend it, the fracture was in the middle. That seems to be because the rotating causes the forces to be distributed lengthwise, effectively rendering the stick in equilibrium. That combined with the pent-up energy stored in the twist allowed a return to its original shape and not a deformation which results in a non-clean break (Choi, Ouellete "What").
But now you may wonder how to cook a perfect pot of pasta? Nathanial Goldberg and Oliver O'Reilly (Berkeley) decided to find out by modeling the physics of the situation. They used prior research pertaining to rods, Euler's elastic theory, and to simplify the modeling assumed no sticking of the noodles nor that the thickness of them mattered. To compare to the model of boiling water and pasta, 15 second differential pictures of a pot of pasta in room temperature water and noted "the length, diameter, density, and elastic modulus" changes as the noodles were hydrated. Yes, its not exactly the normal conditions of making pasta but modeling needs to start simple and grow in complexity. General matching between the model and reality was good, and patterns in the curling of the noodle indicated level of softness. Future endeavors will hope to use the models and find the exact conditions required for that perfect pasta (Ouellette "What").
While we are talking about delicious foods, we have to talk about the clumping of those last few pieces of cereal in our bowl of milk. Turns out that a lot of physics happens here, involving surface tension, gravity, and orientation all playing into in what is known as the Cheerios effect. Each piece of cereal is low in mass and so cannot sink but floats instead, deforming the surface of the milk. Now get two pieces near each other and their collective dips merge and form a deeper one as they meet each other. Capillary action at its finest, people. To actually measure the forces is challenging because of the scale involved. So Ian Ho (Brown University) and his team built two small plastic cereal pieces with a small magnet inside one of them. These pieces floated in a water tank with electric coils underneath to measure the forces at play. With only one piece having a magnet, it was the litmus to see the force of the pieces separated and what it took to drive them together. Surprisingly, they found that as the pieces pull each other in, they actually lean into the pull, tilting at an angle that actually enhances the meniscus effect seen (Ouellette "Physicists").
One of our favorite childhood objects has a lot of amazing things going on for it. Its high elasticity gives it a large coefficient of restitution, or the ability to return to its original shape. No preferred orientation of the balls has a better elasticity to it. In fact, this is partially why they act like a light ray off a mirror: If you hit the ball at an angle to the ground it will bounce off at the same angle but reflected. As the bounce happens, practically no kinetic energy is lost but what is becomes thermal energy, raising the temperature of the ball by about a fourth of a degree Celsius (Shurkin).
I can hear it now: “No way friction can have a complicated piece to it!” I thought so too, since it should be the interacting of two sliding surfaces. Get lots of surface irregularities and it becomes harder to slide, but lubricate appropriately and we slide with ease.
Therefore, it should be interesting to know that friction has a history to it, that prior events impact how friction operates. Researchers from Harvard University found that not only is just 1% of two surfaces in contact at any time and that frictional forces between two objects can decrease if we take a break, implying a memory component. Crazy! (Dooley)
By now you’ve likely heard about the phenomena of the slinky that defies gravity. Video on the internet clearly shows that if you hold a slinky in the air and release it, the bottom seems to remains suspended despite the top coming down. This doesn’t last long but it is fascinating to watch, for it seems to fly in the face of physics. How can gravity not be pulling the slinky back to Earth right away? (Stein)
Turns out, the time of the effect clocks in at 0.3 seconds. Surprisingly, this levitating slinky takes the same amount of time on any planet. That is because the effect is partially contributed to a shockwave effect, but also because the slinky is a “pretensioned spring” whose natural state is compressed. When held in the air, the Slinky’s desire to return to its natural state and the force of gravity cancel out. When the top is released, the slinky returns to its natural state and once enough of the slinky is compressed, that information is conveyed to the bottom and so it starts its path to the Earth’s surface also. This initial balance works the same for all planets because it’s the gravity that causes the stretch in the first place, so the forces aren’t the same but they balance the same way (Stein, Krulwich).
So, how could we manipulate this to increase our levitation time? Well, the slinky has an effective center of mass that falls to the Earth, acting like the object condensed to a point. The higher that is, then the more time the effect can take place. So If I make the top of the slinky heavier, then the center of mass is higher and so the effect is stretched out. If the slinky is made of a sturdier material then it would stretch less, decreasing the tension and therefore (Stein).
Most of us can do this, but few know why it happens. For many years, the explanation was that fluid in between our knuckles would have cavitation bubbles in them that would lose pressure as we expand the joints, causing them to collapse and make a popping sound. Just one issue: Experiments showed how after knuckles were cracked that bubbles remained. As it turns out, the original model is still valid to a point. Those bubbles do collapse, but only partially to the point that the pressure outside and inside is the same (Lee).
More topics are out there, of course, so check back in every once and a while as I continue to update this article with more findings. If you can think of something I missed, let me know below and I will look more into it. Thanks for reading, and enjoy your day!
Choi, Charles Q. “Scientists Crack Spaghetti Snapping Mystery.” Insidescience.org. AIP, 16 Aug. 2018. Web. 10 Apr. 2019.
Dooley, Phil. “Friction is determined by history.” Cosmosmagazine.com. Cosmos. Web. 10 Apr. 2019.
Gwynne, Peter. “Research Projects Reveal How Wrinkles Form.” Insidescience.org. AIP, 06 Apr. 2015. Web. 10 Apr. 2019.
Krulwich, Robert. “The Miracle of the Levitating Slinky.” 11 Sept. 2012. Web. 15 Feb. 2019.
Lee, Chris. “Cavitation dilemma resolved in knuckle-cracking model.” Arstechnica.com. Conte Nast., 05 Apr. 2018. Web. 10 Apr. 2019.
Ouellette, Jennifer. "What to know if spaghetti is al dente? Check how much it curls in the pot." arstechnica.com. Conte Nast., 07 Jan. 2020. Web. 04 Sept. 2020.
Stein, Ben P. “Secrets of the ‘Levitating’ Slinky.” Insidescience.com. American Institute of Physics, 21 Dec. 2011. Web. 08 Feb. 2019.
Shurkin, Joel. “Why Physicists Love Super Balls.” Insidescience.org.. AIP, 22 May 2015. Web. 11 Apr. 2019.
© 2020 Leonard Kelley