As many of you dread your Physics 1 or Physics 2 exam, I do not intend to haunt even your holidays with force diagrams and right-hand rules. Rather, I’d like to point out some everyday festive scenarios for which a little knowledge of physics can help you see behind the hood of this universe.
1. If your family is old-fashioned enough to buy a real Christmas tree, you will have to plant the uprooted evergreen in a stand and drive screws into the trunk to secure the tree. You will want to make sure the tree is not crooked when you drive the screws. If two people with two different angles both agree that the tree looks perfectly upright, then it is guaranteed to look perfectly upright at every other angle. It is easiest to detect and correct crookedness from two perpendicular lines of sight, but that is not required.
2. When you place the heavier ornaments on the shorter branches of the tree, you minimize the torque on the branch. Though your knowledge of rotational kinematics will not take you much further, because the branch is not rigid but bendy. The more you think about the physics of everyday objects, the more you discover that the textbook equations and concepts often serve only as approximations that can only take you so far.
3. If one bulb on a strand of lights goes out but the rest stay lit, you have parallel circuits to thank. If the lights were wired in series, the death of one bulb would spell the demise of the entire strand.
4. Ice is slippery. Why? You might think it’s because there is a layer of water on the surface. If you are really sharp, you will argue that when you increase the pressure on the ice by walking on it, you decrease its melting point, causing the layer of water to form on the surface. You would be correct, but this effect does not make ice slippery. In most cases, the increased pressure does not reduce the melting point enough to form the layer of water. Ice is actually most slippery when there is no water present — at about twenty degrees. The real reason is that the surface of ice (by nature, by its chemical properties) has a thin layer of freely moving molecules, giving ice a fluid, water-like surface. So, the original intuition was not far off, but the effects of pressure and melting point are irrelevant.
5. Do not try too hard to open gifts at the exact same time as your siblings. Einstein informed us that the “same time” for your mom standing still taking a picture is not the “same time” for your dad walking back from the kitchen with his coffee. Though, admittedly, this effect (dubbed the “relativity of simultaneity”) is negligible unless your dad approaches you at a speed faster than around sixty-seven million miles per hour (in which case you might want to check what’s in his coffee).
6. If your mom, asking you to set the table while she makes dinner, says, “I can’t be in two places at once!”, you can reply, “Mom, if I close my eyes then your quantum wavefunction exists in a superposition of states, so actually you can be in two places at once.” Your mom, though, will have the last word: “Well, because I’m doing all this work, my wavefunction has become entangled with my surroundings and has thereby become decoherent. Thus, quantum effects, such as superposition, no longer apply, so I indeed cannot be in two places at once. Please set the table.”
7. Look for the constellation Orion (one of the few constellations which actually looks like its namesake) in the southeast with the three bright stars of his belt sloping up and to the right.
8. On the winter solstice (December 21), all twenty-three and a half degrees of the earth’s tilt will be directed away from the sun (in the northern hemisphere). On this shortest day of the year, the sun will be up for only seven to nine hours, depending on your latitude. From then on, the days will start getting longer again. According to one theory, Jesus was born on the winter solstice (Dec. 25 to the Romans) and John the Baptist on the summer solstice, which is fitting because John prepares the way of the Lord Jesus, whose light only grows brighter after His birth.
Richard Taylor is a junior from St. Louis living in Keenan Hall. He studies physics and also has an interest in theology. He encourages all readers to send reactions, reflections or refutations to rtaylo23@nd.edu.
