“Can You Solve These 5 Physics Phenomena”

I’ve been sick, knocked on my ass for the whole week, hence the lack of posts. However I saw this on IFLS, and wrote an explanation while I catch up on lab work. Science!!!

Watch the video first, or my explanations won’t make any sense…

1. Friction increases when a finger gets closer to the center of mass because more mass is supported by that finger. Hold your fingers at different angles, and it won’t work because the coefficient of friction for each finger is different.
2. Angular momentum is transferred to the shortest radius where the spin is more favored. If you think it’s because the mass is unbalanced, try something uniform. It will behave the same as the phone.
3. Water bending due to static charge is an example of diamagnetism, an induced magnetic attraction in the presence of a magnetic field. It’s sort of like high-fiving someone with an open hand, the force of which causes his hand to curl around yours. The negatively charged cup repels electrons to the opposite side of the water molecule just a tad, inducing a more polar, and hence, more attractive ;), water molecule. This is why the negative static charge works better than a regular old magnetic field. However, very strong magnets can also cause water to bend like this.
Unfortunately, his explanation of the polar water molecule is incorrect. He is incorrectly describing water like a salt with equal numbers of positive and negative charges. Water molecules are free to re-orient themselves in line with a magnetic field (and they do), but that is not the complete cause for the curvature.
4. Speaking of magnets, cereal contains iron, a lot of iron. Check the label. That’s not some exotic form of iron that is blended into your food. It’s small filings of iron metal. You can even extract the filings by blending the cereal into a paste and attracting the filings toward a powerful magnet.
5. You all know that hot air rises. Do you know why? Gas molecules at higher temperatures move more quickly, bumping into each other and spreading out like the most hyped up rockers in a mosh pit. That causes this high temperature area to be less dense than low temperature gasses, and the low temperature (higher density) gasses sink due to gravity and push the hot air upwards.
As the bag burns from the top, the hot gasses and air rise, while air remains cold underneath the flame. However, as soon as the flame reaches the bottom, the zone of hot air extends all the way to the plate, and cold air quickly rushes in to take it’s place. The small fragments of unburned bag are propelled by this rush of cold air. Remember, it’s not just that hot air rises, it’s that cold (denser) air sinks to take its place.


I’m not wild about science education videos that simply seek to induce an “isn’t that cool?” response without any follow up. That’s not to say that he should have given full explanations. However, he should have ended each segment with “what would happen if instead I…”. If the point is education rather than giving away the answer, thinking about problems in terms of experimental design is very effective. This video simply reinforces the perceived inaccessibility of counterintuitive phenomena.


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