# TheSigFig

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1. ## If physics stopped working

If someone asks why physics is so important, tell them that the world just wouldn't work without it. Not the way we know it at least. As this is my final post of the year, I thought it'd be a cool idea to talk about what the world would be like if certain parts of physics didn't exist. In a previous post, I discussed the difficulty that would come with living in a world without friction, and I also mentioned how without electrostatic force, objects would phase right through each other. It would also mean current electricity would not exist, but what would that matter if we couldn't even use it. If gravity didn't exist, objects would keep moving until they hit something, and everything in space would just drift endlessly in one direction. Which means the earth could potentially drift into another planet or a star, which wouldn't be good. Without magnets, we'd have to find different ways to generate electricity or make power, and compasses would have never been invented, so navigation wouldn't be as easy. So yeah, physics is pretty important, unless you prefer a world that doesn't work. It's what makes our world possible.
2. ## Hey, no pressure

Pressure is an interesting topic. It's used all around us in things we take for granted. Soda cans are under pressure, airplanes keep air pressure the same so we can breathe when it's really high in the air, hydraulic lifts take advantage of water pressure. It's everywhere. Forces can act on an object due to differences in pressure, going from high to low. Let's use the soda can as an example. When you open a soda can, it fizzes because of the pressure released. If you were to take a the same unopened soda can, and take it in a submarine far enough below sea level, where the pressure around you and the soda can is greater, you could open it or shake it beforehand as much as you want, and it won't fizz or explode since there's no difference in pressure, resulting in no net force. Conversely, if you go to a higher altitude, and the soda will fizz more. This is the same reason why if a balloon filled reaches a high enough altitude it will pop
3. ## "Floating" above the ground

Technically, objects never really make contact with each other. when you put something down on a table, or stand up on the ground there is a very very tiny gap between the object and the table, or your feet and the ground. This happens because the electrons in the atoms of both objects repel each other. This is what keeps us from going right through objects since most of matter is empty space. But if it's an electrostatic force, why do we only feel it upon "contact"? Well, while atoms are composed of charged particles, they are electrically neutral, and from and since the charge of an electron is so small, even with billions of them, unless they are very close together, the force they exert on each other is so very small it's insignificant.
4. ## The domino effect

As a kid, I liked making extensively large trails of dominoes standing up. Knock one down and the rest would be set in motion. I remember wondering why they tipped over and fell instead of just sliding across the ground when hit. The answer to that is friction. Because of its orientation, when standing up, pushing against it won't just slide it over, but also cause friction to act at the bottom. Because the forces act at a distance from the center of mass, a net torque acts on the object, tipping it over, and causing the same thing to happen to all the dominoes in front of it. If the domino were just flat on the floor, it would just slide since the ground would stop it from rotating around it's center of mass. It's common sense really. It isn't like you can hit fallen domino from the side and expect it to just flip back upright.
5. ## A balancing act

People always seem to try and test their balancing skills in almost every way possible, from stacking things on top of each other, to treacherous tightrope walks. But what exactly does it mean when something is balanced? It means that the object is not moving, so the net force, and net torque on the object is zero. The torque on a free standing object that can cause it to fall is the result of gravity acting on its center of mass while it's not centered. Theoretically it is possible to balance anything, but without some very precise machines, it's really improbable for a person to successfully balance something like a pencil by its tip for example. But sometimes it appears as if something is balanced, then it begins to fall over. This happens because even if the center of mass is a tiny tiny distance off center, it can still be enough for gravity to produce a very small torque, giving it a very small speed that gradually increases as it is accelerated until it falls over. So in order to balance things, sometimes you have to be really, really accurate
6. ## Don't try this at home

Conservation of momentum is a very important law. A rather interesting idea popped in my head earlier pertaining to this. Since momentum is conserved, wouldn't it be theoretically possible to lift off of the ground by hitting the ground fast enough with your hand? (Assuming you don't break something or get hurt.) If you're on a slippery surface or on something with wheels you can push off of a wall and slide in the opposite direction, so wouldn't something similar work vertically? Momentum is always conserved in an isolated system, isolated being the key word. This means that for momentum to be conserved there must be no net force on the system before or after the collision occurs. In the vertical direction, there is the force of gravity acting downwards on the system, so momentum is not conserved. So this crazy idea would not work. The reason momentum is conserved in the horizontal plane on the ground is because that force of gravity is canceled out by the normal force from the ground (or whatever surface it's on) making the net force before and after zero.
7. ## Its all relative

Relative motion can be a bit weird when you really stop to think about it. It may seem to make sense that when we are standing still we don't move, but think about it. Why is it that we don't move when the earth is rotating really fast under us? Friction? Nope, that doesn't answer it. The reason is because while the earth is rotating, whatever point we are on, we move with the same tangential velocity of the earth. So while relative to the ground we may not be moving at all, relative to some observer in space (if we could be seen from space) we are actually moving pretty darn fast. It's the same reason why if you're in a car going 60 miles per hour and throw a ball straight up into the air it doesn't fly backwards. Relative to you, it's not moving at all, but relative to the ground, it's moving with the car at 60 mph. Just an interesting thought I had, and even if you read this thinking "well, of course that's how it works," just remember, to someone else, their mind may have just been blown. It's all relative
8. ## Paper airplanes

I'm sure many of us remember making these out of papers at home, with friends, or in school even though we may have been told not to. You fold the paper into the place, throw it forward, and it glides straight forward. Or sometimes at some weird angle if you didn't do it right. But what keeps them in the air longer than a lot of other things, and what makes them turn weird ways sometimes? Well, in addition to the downward force of gravity, a drag force caused by air acts opposing whatever direction it's moving. This doesn't affect massive objects with certain shapes as much, but light objects like paper certainly feel it's effects. If made and thrown correctly, a paper airplane will have very little air resistance in the horizontal plane, meaning it will keep moving and barely slow down. However in the vertical plane, the paper feels a much greater drag force opposing the force of gravity, keeping it in the air longer. If the plane is thrown at an angle, air resistance will act to oppose it's motion, which will point it in a different direction because of the paper's orientation.
9. ## Resonating bottles

Waves are everywhere. Sound, light, and even matter. They're what let us see the world around us, and what let us hear things (well, other than our eyes and ears respectively). Waves are what make sounds possible. When I was hanging out with a friend of mine the other day, in the middle of a conversation, he blew into the soda bottle he was holding and it made a noise. Being the physics enthusiast that I am, I decided to explain why that happens. Blowing into the bottle produces sound waves caused by air vibrating the bottle, and these waves have a different frequency. Frequency is what determines the pitch of a sound wave. The pitch can be changed by changing the frequency, which changes with either the wavelength, or speed of the waves. Blowing into a bottle of a different size will produce waves with different wavelength and frequencies, resulting in different pitches. In the case of a soda bottle, removing some of the soda will change the frequency as well. Since soda is a different medium than air, the speed of the wave will change in the same length resulting in a different frequency
10. ## AC-DC

Before you ask, no, we're not talking about the band. We're talking about current. Specifically the current that runs through everyone's houses, and some interesting facts about it. For those who didn't already know, almost every household outlet provides alternating current to whatever is plugged into it, yet a lot of electronic devices, like phone chargers, take direct current. So why is AC used? Well, part of the reason is to make use of important devices called transformers. They're those buzzing metal boxes that are usually suspended from poles that hold up power lines or placed near larger buildings. Power plants generate higher voltage than what is used in homes for everyday appliances, so what a transformer does is convert it to a lower voltage. Inside the transformer are coils of wire. Current flows in and enters a coil with a lot of loops in it, inducing a magnetic field, and since it is alternating current, the magnetic field changes. This changing magnetic field is used to induce a current in another nearby coil with less loops. This induces a current in the smaller coil with less voltage. When you plug something like a phone charger into an outlet, that box where the plug is has another smaller transformer in it, along with a circuit set up to convert AC to DC with the proper voltage for what you need to use.
11. ## Suction cups

Suction cups are strange when you think about it. It's just a curved piece if plastic but it can stick to walls. So what makes it so different that it doesnt just fall from the wall? Normally if you try to stick an object to a wall, it just gets pushed away by a normal force. However in the case of a suction cup, when you press it against a surface, the air underneath it is pushed out and creates a vacuum, creating a difference in air pressure. This causes air to apply a force that keeps it against the surface, and friction prevents it from sliding down.
12. ## Death from above

Sometimes, science fiction captures some ideas that are both interesting and terrifying, especially when it's something that could be possible. One videogame from the outrageously large Call Of Duty series, Call Of Duty: Ghosts (seriously, they have made way too many of these games) has a weapons satellite orbiting the earth called Odin, that drops metal rods from space that fall to earth's surface and seem to explode on impact. Seems like complete nonsense right? Well, actually it's a concept that's been floating around for a while called kinetic bombardment. Basically it goes something like this: a rod is dropped from orbit and pulled down by earth's gravity, and builds up speed as it enters the atmosphere. The rod is designed to maximize it's terminal velocity, building up speed and also building up kinetic energy. When the rod hits something, that energy has to go somewhere, so it goes into whatever it hits, in this case, a building or the earth's surface, dealing damage almost like a bomb. It's kind of a scary thought. Thankfully stuff like that is why there's the Outer Space Treaty, so people can't go putting stuff like that into orbit
13. ## A world without friction

What if we lived in a world without friction? Well, it would probably make everything really difficult. And I mean really difficult. One thing that would be made near impossible to control would be transportation. The very way we walk depends on friction between the ground and our feet or shoes, so if we tried walking, we'd slip, fall over, and slide indefinitely across the ground until we make contact with either a flat surface to push off of, or a round surface, like a street lamp, where you could change direction by hooking your arm around and moving in circular motion. Now if that sounds even somewhat amusing, also consider this, what happens if you go too fast? Well since friction couldn't be there to slow you down, you'd either painful hit a solid surface and change direction, or if you hit something softer, like a pillow or something, it might be able to cushion the impact.
14. ## Tug of war

It's always a ton of fun. Even when you do find out that it's not a game about strength, but a game of friction because of newton's third law, which says every action has an equal and opposite reaction. so whatever force is applied at one end of the rope by one person must be applied at the other end in the opposite direction by another person. Then it's all a matter of who can apply a force to surpass that of friction. But I had a strange but interesting thought; what if this happened in the vacuum of space? What if one day two astronauts were randomly floating in space with a rope for whatever reason and one said "hey I've got an idea..." Well if both pulled the rope at opposite ends, depending on their mass, they would both drift towards each other, because their initial total momentum of zero must be conserved, and then collide, and possibly drift back to where they started if the collision was elastic. If this was the case, they'd probably want to pull back on the rope so they don't drift away in space indefinitely. But unless they applied a precise amount of force to stop them from moving away from each other, they would just move towards each other and the process would repeat. Maybe tug of war in space isn't such a good idea
15. ## Boomerangs: why they come back to you

I'm sure many of us have seen boomerangs in cartoons, or movies, or in real life, and wondered what makes these seemingly magical things come back to the thrower. Well it's actually an interesting combination of things that let them always come back. First is the way it's shaped. Normally a boomerang is two fins, shaped very similarly to plane wings, that are attached at an angle. When thrown, because of their plane wing like shape, air passes more quickly above the fins than underneath, causing a lift force due to a resulting difference in air pressure. For it to come back it must be thrown at an angle close to vertical. Because the boomerang's fins are attached at an angle, this, combined with the forward motion given by the throw, results in more air hitting whichever fin is at the top of the spin at a greater rate while it's spinning, resulting in a greater lift at the top of the boomerang. But because it's rotating, this lift force acts more towards the front of the boomerang, rather than the top, turning it and giving it a circular flight path. Think of it sort of like a bike in how if you tip slightly to one side while it's moving, rather than falling over, the bike turns. Quite alot going on in such a seemingly simple object
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