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## 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.

## 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

## "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.

## 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.

## 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

## 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.

## 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

## 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.

## 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

## 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.

## 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.

## 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

## 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.

## 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

## 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

## Hoverboards

Once thought to be a mere figment of science fiction, these floating skateboards are now all science and no fiction. However, as with almost all technology, it's not without its limitations. A couple of months ago, Lexus created the "slide" hoverboard, a piece of machinery that works because of magnetic force... meaning it only works on magnetic surfaces, an obstacle conquered by the creation of a custom skate park in Spain where most of the surfaces are made to be magnetic. Despite this limitation the way it works is quite interesting. Within the board are nitrogen cooled superconducting blocks, which have no electrical resistance. The magnetic field from the surface below it induces an electric current, and creates an opposing magnetic field from the superconductors due to a phenomenon called the Meissner effect. These magnetic fields create a force that allows the board to be able to hover. So while we might not be able to just pick up a hoverboard and ride it around anywhere, its cool to see that it's at least possible

## Satellites

Through the years many man made satellites have been placed in space for various purposes. But what keeps them up there without crashing into eachother so debris doesnt fall to the earth? With around 2000 satellites drifting around the planet, something has to stop them from colliding, right? When satellites are launched into orbit, their orbit is recorded, and others are launched with orbits such that no two will collide. However, over very long periods of time orbits can shift slightly, so technically nothing stops them from crashing into eachother. Fortunately even in the event of a crash, falling debris is no danger. As small pieces of satellite from a crash fall towards the earth, they experience a large drag force upon entering the atmosphere, generating heat, and causing the falling objects to burn out long before they get to a dangerous distance

## Nerf guns

I'm sure some of us remember these brightly colored blasters that lined our toy boxes as kids, and the backyard shenanigans shared with friends. But what many of us probably didn't realize is that what we held in our hands was a spring loaded product of physics. When pumped back, a spring inside the blaster would be compressed, and held in this state by a small contraption attached to the trigger. When the trigger is pulled afterwards, this contraption moves out of the way, allowing the spring to return to its equilibrium position. A Platform on the end of the spring then uses the spring's restoring force to push air from inside the blaster, which propels a foam dart forward and out the front. From there, gravity takes over until the dart hits the ground, or another surface.

## Oh Christmas Tree

Ah, the holidays: a time of cold weather, happy feelings, and peppermint flavored everything! What's not to love? with everyone getting their decorations up right around now i thought i'd talk about a simple thing with some simple physics to it: putting ornaments on a Christmas tree. If you get a real tree every year like me and my family do, then you probably run into the problem of trying to figure out what ornaments to put where because certain ones on certain branches will bend the branches, and cause the ornament to potentially fall off of the tree. Why does this happen? well that's because of torque that the weight of the ornament applies to the branch around it's rotational axis, which in this case is the trunk of the tree. if a branch bends too far when an ornament is placed, it simply means the branch has a lot of torque applied to it, and there are two ways to fix this. the first is to put a smaller ornament on that branch. this means less weight, and therefore less force applied. the other solution would be to move the ornament closer to the center of the tree. since torque is directly proportional to the distance which the force is applied, moving the ornament closer to the tree would decrease this distance, thus decreasing the torque

## Spinning coins

Ever been really bored and done something really random? Ever been really really bored and pondered the physics of said random act? I know I have. Just the other day while sitting at a table, I got bored and had a penny in my pocket, so I decided to spin it on the table in an attempt to satisfy my boredom. After about five minutes I made some interesting observations. One thing I noticed is that every time it spun, it would slide across the table. At first I thought this was because the table was at a slight angle, and gravity was causing it to slide down, but after some closer observations I learned that this was not the case, as the table was level. After some more thought I figured it out. Every time I would spin it, the reason it would move was because its axis of rotation was not 100% perpendicular to the table. Because of this, the edge of the coin that was touching the table had a frictional force acting opposite of the direction of the edge's tangential velocity, causing it to accelerate and move along the table

## Superpowers

Superpowers would be awesome. I think that's something we can all agree on right? Like how awesome would it be to fly or be able to teleport places? It sure would save alot of time walking to and from school or work every day. But as great as all that may seem, even if superpowers were possible who's to say they'd be safe? Let's take a look at another superpower that would make traveling places alot faster: super speed, like the Flash. Being able to run faster than a speeding bullet sure would seem cool, but unfortunately even if one could do that, there would be several dangers to it. The big thing would be the danger of collisions. Running into something at this speed would be incredibly deadly. Let's assume the person with super speed is running as fast as a bullet fired from a gun, and lets assume they crash into something,  and the impact time is a tenth of a second. The average bullet travels at 2500 feet per second, or 762 m/s, and the average person has a mass of about 80.7 kg. Doing the math (M*deltaV=F*deltaT) results in a whopping 614934 Newtons of force. Way more than any human can survive.

## Driving and Dynamics

After learning about and studying physics for a while, sometimes you just start thinking about how it applies to what you're doing right now. And while it may warrant a few odd looks from friends and family if you're like me and voice those sudden realizations, it can be quite fascinating, as there are some simple things that have some interesting explanations. Like how walking works because of a normal force the earth applies on you as your leg pushes down. As I was taking driving lessons one day, I started thinking of the way physics works when someone is behind the wheel. One thing noticed more was how when a car turns, the passengers tip over a bit in their seats to the other side of the car, and how when the car stops, everyone leans forward a bit. The reason this happens is because of inertia. Newton's first law states that an object in motion tends to stay in motion unless acted on by an outside force. When a car turns one way, say to the left for example after moving forward, your body wants to continue moving forward, but is dragged to the left by forces exerted by the seat on your body. This causes your body to tilt in the direction it was initially going, but because the car is turning, it appears to tilt to the side, in this case the right side since that is the side closest to the initial forward direction. The same thing applies as the car comes to a stop. As the car stops, your body wants to keep moving forward, but is held back by forces exerted by the seat and seatbelt opposing the direction of motion

## Gravity in Gaming

Whenever it comes to science fiction, in addition to all the impossibilities that already exist, the laws of physics tend to be glanced over or tossed aside for the sake of simplicity or other reasons. This time, I'm talking about gravity, specifically in the game Destiny. The game allows you to explore various planets and locations in our solar system throughout your adventure. so being on different planets means gravity has to change, right? well for the sake of in game mechanics this is unfortunately not the case, as everything works exactly the same in every location, but how would differences in gravity make things different? well, due to differences in the acceleration due to gravity (g), the force on an object would be different on each planet, meaning jumping would be easier or harder, and bullets would travel farther or shorter distances depending on if g is larger or smaller than that of earth. Also, two of the game's locations would be impossible to even set foot on. The first being the vestian outpost, a space station situated in the middle of the asteroid belt, and the second being the dreadnaught, a massive enemy spaceship stationed in the rings of Saturn. both would be impossible for the same reason, there is no way for either of them to have or simulate a significant enough amount of gravity.

## Laser guns and Lightsabers? Not a chance

In the wonderful world of Star Wars lies yet another example of impossible technology that the laws of physics have no way of explaining: lasers used in both guns and the iconic lightsabers. The lightsaber is basically a beam of light and heat energy on a handle that can slice through pretty much anything with the exception of another lightsaber. as much of a cool idea as this may have appeared in our heads, there is unfortunately a number of reasons why lightsabers won't be real any time soon. The first reason is the way they behave. The beams act as though they were solid objects, able to crash into each other and repel each other, and extending and retracting from the handle at the push of a button. This is a beam of energy, and energy certainly is not matter. If they were any bit realistic, the beams would simply pass right through each other if they were crossed. another reason they wouldn't work in real life is the fact that the beam suddenly stops at a certain point, and still has the same effectiveness throughout. it wouldn't be possible to have that much energy focused at one spot without it dispersing somewhere else. even if it were possible to generate the beam, it would be kind of like fire. the tip where it reaches up to would still burn, but the most energy would come from closer to the source. energy can't necessarily be contained, and that's also why laser guns wouldn't work. the focused energy from the laser would most likely transfer to the gun before it even hit anything, deforming or melting it. so unfortunately, as cool of an idea as it may sound, lightsabers won't be possible

## Trampolines

Trampolines are always a ton of fun, but they're one of those everyday things a lot of people don't really question. it's one of those things people just take as common sense, but what makes them work the way they do from a physics perspective? how is it that they can propel a person so high in the air, and why is it that jumping on one somehow sends a person higher than simply jumping on solid ground? the answer is that on a trampoline, there is an extra force acting on you each and every jump. as one lands from their first jump, the trampoline stretches downward a certain distance, extending springs along the outside. as they jump back up, there is an extra restoring force upward from the springs and trampoline added to the force of the person propelling themselves upward, resulting in a greater height achieved by the jumper. this force increases as the jumper applies more force to the trampoline as it is displaced a greater distance from its equilibrium position. Just jumping on solid ground doesn't get you any higher simply because the ground obviously doesn't move, so any extra downward force you exert might just result in sore feet after a while