# bazinga818

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## Blog Entries posted by bazinga818

Honestly, this whole E & M section of Physics C has not been going so great for me. We're supposed to have our last unit test on electromagnetism tomorrow, but I took it today because I won't be here tomorrow. We finish it the Monday after break, and it's safe to say I left about 75% of that test blank because I didn't know the answers.

I think I struggle with concepts more than anything. I just can't visualize the problem like I could in mechanics, so none of the processes we go through to get answers seem logical to me.

Anyway, I need to work on memorizing formulas too. I know induced current is big and necessary, but unfortunately today I forgot that equation during the test. I also need to study capacitors and inductors and how they act in circuits, as well as how to use all those equations with e in them in the RL/LC circuits .

I think a huge contributor to my misunderstanding is how I watch the videos. I watch them and take notes, but don't always comprehend what the point(s) of the video was/were, and then I go a couple days without looking at my notes on them and I forget almost everything.

As you can see, I have my work cut out for me over break. I know this isn't a typical blog post, but I also know that I am running out of ideas, and this helped me work out my issues which is good.

Until next time,

bazinga818
Since I just rode up one, and because I can't think of anything else to write about at the moment, I guess Ill do the generic elevator blog post.

So, elevators. One of the first things we did in Physics B when learning about free body diagrams, was practice elevator problems. First, in all out FBD's, we would have to draw our weight=mg pointing down because the force of gravity acts downward. Then the normal force, or the force of the elevator pushing up on your feet, would point upward.

If the elevator was not accelerating, weight=normal force. However, if it accelerated upward, the floor pushes on your feet with an even greater force, so if you were standing on a scale you would weight more than your actual weight. In accelerating downward on a scale, the scale would show you weighing less than your normal weight.

A shorter one, but you get the idea. Thanks for reading.

Until next time,

bazinga818
See what I did with the title there? I'm so clever.

So, echos. An echo happens when you say something or make a noise and the sound waves from your mouth bounce off a hard surface and rebound back to you, which is why you hear what you said again and again and again. This is why echoes are common in caves, because you're surrounded by hard surfaces.

We know that when a wave reaches the end of its medium, it undergoes a certain process depending on how it's medium ends. Transmission/refraction, diffraction, and the one that causes echoes: reflection.

Awhile ago I stumbled upon something really cool involving echolocation, which is the ability to make sounds and determine where and sometimes what certain objects are in a room. I watched an especially awe-inspiring video, showing blind people that had learned to use echolocation; an object was placed on a big table in front of them, and by making clicking noises with their mouths, they were able to determine where on the table it was placed and even what shape it was. Some even guessed the objects.

I wish I could link the video, but since I can't I do hope you'll try to look it up and maybe someone can find it. I thought that was pretty amazing, to be able to see in a completely new way. Yet another awesome application of physics.

Until next time,

bazinga818

We already talked about conservation of energy, so now let's talk about conservation of momentum. Momentum is a vector quantity, meaning the direction it's in matters. When the first ball is dropped into the second ball, the second ball must keep moving in the same direction, and the first ball doesn't just bounce off the 2nd in the opposite direction; this would be a change in momentum, which cannot happen without the application of an outside force.

So in order to conserve momentum, the energy must move in the same direction through all five spheres.

Of course, Newton's Cradle isn't a completely closed system so as to warrant conservation of momentum, as the force of gravity and friction will always act as outside forces. But for the sake of this explanation, we'll assume we live in a perfect world without gravity or friction and everything is a closed system. Then, the collisions in Newtons Cradle would be perfectly elastic, where kinetic energy is conserved as well as momentum.

A bit drab, but hopefully you stayed awake till the end. I'll try to make the next one more engaging, but it's hard to find motivation in a dark hotel room while you're leaning over your phone listening to your parents snore and typing about physics instead of partyin it up in Pittsburgh.
We've all seen it - that contraption with 5 metal balls hanging side by side on strings? You lift one to the side as if it were a pendulum, let it go, and it swings into the others - causing the ball on the very opposite side to go up. This is called Newton's Cradle, named after the big guy himself.

There are a number of physics laws at work here. First, the law of conservation of energy: as potential energy is maximized and kinetic energy is zero when the end balls swing to their highest point, thus kinetic energy is maximized and potential energy is zero at the bottom of its path. However, while kinetic energy is maximized, the ball is suddenly stopped short by the next ball at rest at the bottom of this path.

The end sphere stops moving and it's kinetic energy becomes zero, but since the law of conservation of energy states that energy cannot be created or destroyed, that energy has to go somewhere. So it goes into the second sphere, on into the third, fourth, and finally transferred into the fifth where this ball uses the transferred kinetic energy to move away from the pack in a pendulum-like arc upward, mirroring the first sphere's movements.

Voila! Conservation of energy at its finest, explaining cool doo-hickies like Newtons Cradle. There's more physics to this contraption, but I think I'll expand on it more in my next blog post.

Until next time,

bazinga818
Recently I sat at the table eating dinner, when I noticed a flutter in my peripheral vision, drawing my attention. I turned my head to see my cat batting at a cat toy someone had hung from the table...one of those sticks with the string attached and a feather or fluffy thing at the end, ya know? You wave it around like a wand and your cat pounces after it?

Anyway, someone in my family had set it up so just the string and attached feather hung down over the table, just within my cat's reach. She batted at it playfully.

It was then that I realized...hey! More real-life physics applications! This cat toy was an example of a pendulum!

When we learned about pendulums, we learned that they have a period of oscillation, or time it takes for them to complete one cycle, to swing forward and back to its original position. We learned that pendulum's periods of oscillation DO NOT depend on the mass of the object at the end of the pendulum (as with springs), but rather only depend on the length of the pendulum and the acceleration due to gravity.

For a perfect pendulum (weightless string, perfect conditions, etc), the equation for the period is T = 2(pi)radical(L/g), or 2 pi times the square root of length of the pendulum over acceleration due to gravity.

Unfortunately, my cat's toy wasn't a perfect pendulum, and the feather at the end inhibited the period time due to the air resistance it created...but oh well, she didn't seem to mind.

Until next time,

bazinga818
Recently (on a much cooler day), I discovered something while driving to volleyball practice at night. It was chilly so I had the heat on in my car, but just on low. Upon turning on the highway, I suddenly noticed that the heat seemed to have been turned up! That wasn't right, how could it do that on its own?! I double checked it, but the switch hadn't moved; the heat was still on the lowest setting.

So why did it feel like hot air was blowing twice as fast into my face? Well, when I thought about it, the answer was simple: inertia. As the car accelerates forward (as it does when entering a highway), the objects - including hot air - inside the car want to stay put. This is the same reason why you feel thrust forward when you slam on the breaks, or slammed against the wall when you make a sharp turn. Your body wants to keep moving in a straight line due to inertia (as Newton says, "an object in motion tends to stay in motion").

So, what does this have to do with the hot air in my car? Well, it too has inertia and wants to stay at rest unless acted upon by an outside force, so when I accelerated onto the highway, the hot air stayed in place. Since the car itself was accelerating forward while the air stayed put, it made it feel like the hot air setting had been turned up as it blasted in my face. In reality, it was me (and the car) accelerating into the hot air.

Anyway, I thought this was pretty cool. Hopefully you thought so too! Thanks for reading.

Until next time,

bazinga818
It was first Aristotle who discovered what is now known as the Mpemba effect: that hot water actually freezes faster than cold water. Scientists have struggled to explain this for years, until recently.

We all know that "water" is made up of two hydrogen atoms and an oxygen atom, more accurately known as H20. Cold water is made up of short hydrogen bonds and long O-H covalent bonds, while the opposite is true for warm water. It is these hydrogen bonds that act weirdly and have drawn the attention of scientists.

Some strange, unexplainable facts about these hydrogen bonds:
1. Although they're generally weaker than covalent bonds, they are stronger than the "van der Waals" force that is the sum of all attractive forces between molecules.
2. Chemists have suspected for awhile now that it is these hydrogen bonds that give water some of its weirder properties, such as allowing its boiling point to be so much higher than other liquids of similar molecular make-up. The hydrogen bonds hold it together very well.

Anyway, though the hydrogen bonds bring water molecules into close proximity, the molecules are naturally repulsed by each other and as a result stretch away from each other and store energy, increasing heat.

When the molecules shrink again and lose their energy, they begin to cool quickly as a result. Voila! The Mpemba effect.

That was a simplified explanation from someone who hasn't touched Chemistry in two years, so I apologize if any of it is incorrect. Hope it gave you some insight, at least!

Thanks for reading. Until next time,

bazinga818
Warning: this blog post may get a little gross if you don't like mucus-related physics talk. Reader discretion advised.

So, ever wonder just how fast you sneeze? Or rather, how fast the snot comes out of your nose when you sneeze?

Well, so did Adam and Jamie on Mythbusters. They investigated a myth that when sneezing, the mucus can eject from your nose at speeds of up to 100mph. That myth was busted though, and they instead found snot-rocket speeds to be only about 35-40mph. Still - that's the speed a car goes on most streets, and it's pretty fast.

Imagine how far you could shoot snot rockets...the snot would act as a projectile that we could use our projectile equations on in order to find the initial velocity. Jamie and Adam did just that - see how far theirs went:

Gross! Well, that's about as much as I can take on the subject...thanks for reading! Hope you found it interesting.

Until next time,

bazinga818
We've all heard the myth. Drop a penny from the top of the Empire State Building, it will gain enough velocity to do considerable damage to someone standing on the sidewalk - plunge a hole through their hand, or, in more gruesome versions, their head.
Though at first this thought seems plausible (considering the height of the Empire State Building and the acceleration due to gravity), it's important to realize that - due to other important factors - this myth is busted.

When we first release the penny from the top of this skyscraper, it begins to accelerate downward at 9.8 m/s^2, the acceleration due to gravity. If the only force on this penny were the force of gravity downward, it would continue to accelerate at a constant 9.8m/s^2 until the moment it hit the sidewalk. Since we know the height of the Empire State Building is about 381m, and we also know the acceleration is 9.8 m/s^2 and initial velocity (Vo) is zero, we can calculate the final velocity (Vf) using our kinematics equation: Vf^2 = Vo^2 + 2ax.

Plugging in those numbers, we get that the penny would be traveling about 86.4 m/s just before it struck the sidewalk or person on the sidewalk. For those of you who find it hard to comprehend just how fast this is (because here in the US we say "screw the metric system!" ), this translates to roughly 193 mph. Yeah, that's pretty fast.

But wait! There's more! We forgot to account for one crucial detail, the very detail that makes this myth a bust: drag.

As the penny falls, it experiences another force - the force of drag, or air resistance, acting opposite the force of gravity. For its weight, the penny drags an awful lot of air behind it. As a result, it reaches terminal velocity at only about 25 mph.

So, there you have it. Because of the force of drag/air resistance, tourists below the Empire State Building have nothing to fear from falling pennies.

Hope you enjoyed this blog post!

Until next time,

bazinga818
The Physics-C midterm approaches.

While frantically searching the depths of my mind (and the internet) for an idea for my last blog post, I looked up to realize the time and scolded myself for not finishing these blog posts earlier. Why do I always wait until last minute? This is time I could have used to study.

So in a feeble attempt to finish in time to cram in some legit studying (because I don't think blog-post writing counts as studying) for both Econ and Physics tomorrow, I decided to write about the midterm and what I'm worried about/need to study, etc.

Let me start off by saying I am so so happy there is no E&M on this midterm. I'm definitely dreading the months to come in learning more about that subject, and having to take an entire exam on it in May. Yikes.

But luckily, our midterm is all Mechanics. Still, I definitely have a lot to be worried about. Most of what I'm nervous for is stuff we've learned this year, especially the long derivation-heavy physics-y type problems we'll have to do or know for the part two's. Just part two's in general, I know I'll have trouble with. I think the best way to remedy this would be not only to look over the practice FRQ's we've done, but also to look over the problems we've done in our notes and maybe try a few on my own.

I've noticed I also have trouble with vectors and dealing with things in more than one dimension or direction. I sometimes ignore things I'm not supposed to ignore or combine things I'm not supposed to combine or something along those lines.

I'll definitely have to look over those 2D momentum problems, for one thing. Also, dealing with real pulleys will inevitably throw me off. Moment of inertia problems, too.

As far as the multiple choice goes - I feel a little better about that, but still not super confident. I often make stupid mistakes, so I'll need to try to minimize those. And timing - I definitely need to watch out for that.

Okay, it's getting late so I'm going to wrap this up and squeeze in some last-minute studying before I crash for the night. At least I don't have to worry about getting my blog posts done anymore!

Good luck to all the physics students (regents and AP) taking their midterms this week! We're halfway there. (insert Bon Jovi jam session here).

Wow, I must be really overtired. Thanks for listening to my rant!

Until next time,

bazinga818
Cow tipping - is it really possible? We've all heard about that awesome prank the teenagers of our parents' and grandparents' generations used to pull...but can it really be done?

First off, I'd like to assert that in no way do I condone cow-tipping or the bullying of any other farm animals. Because hey, cows are people too.

Anyway, onto the physics. First off, cows don't even sleep standing up, contrary to popular belief. So, assuming they stay in place and don't run away when you try to sneak up on them (an unlikely wager to begin with, because who wouldn't run away when someone was trying to push them over?), once you started pushing, they'd do everything in their power not to be tipped over.

Cows weigh a lot - we know this. And according to Newton's 2nd Law, F=ma, you'll want to apply a big force as fast as possible to have any chance at knocking the cow over before it can react.

Adapted from Popular Mechanics, using the work of Margo Lillie and Tracy Boecher.

So you see, it's pretty impossible for one person to tip a cow, even if cows did sleep standing up - they're just too heavy. You'd need at least two people for that, and 5 or 6 if they cow were awake and able to take a wider stance and brace itself better against your cruel intentions.

And it's a good thing too - I mean come on people, the poor cows.

Thanks for reading, hope you don't try to test this one out for yourself!

Until next time,

bazinga818
I recently stumbled upon a question that definitely made me think twice. And then twice more.

If you carry firewood to the top of a hill, and then burn it there, what happens to the firewood's gravitational potential energy? Does it disappear?

Crazy, I know. The equation for gravitational potential energy is mgh, or the mass times the acceleration due to gravity times the height. If you burn the log up into ashes with substantially less mass, what happens to the rest of the gravitational potential energy the logs had when you carried them up the hill?

Honestly, the hill part doesn't even matter. Whether you burn the wood up on the hill or in the valley below, it's still gone either way. The hill just makes the height component of gravitational energy easier to visualize.

But where does this seemingly lost energy go? It can't just disappear right? All we've ever been taught in physics is that energy is conserved! Right?!

It's true, it can't disappear - it just becomes harder to find. When the wood is burned, a lot of the energy escapes in the gases released from the fire. The gases are released over a long period of time as the fire burns, so it's hard to visualize them weighing as much as the wood you're burning - but it's true, just about. If you compressed all the gas that is released from the moment you start burning the wood to the moment the last ember crumbles, it would weigh just about as much as the wood did originally. Thus, the same potential energy.

So the energy didn't go anywhere, it just escaped in a different form. There are some other factors in play here I still don't quite understand, but this is the gist. Maybe I'll look into those other factors and expand on them in a future blog post.

This is where I learned about this topic, and you can too: howeverythingworks.org. This guy really knows his stuff, and probably explains it better than I can. Make that definitely explains it better, since I still don't fully understand it.

Hope I made a little bit of sense anyway. Thanks for reading!

Until next time,

bazinga818
Did you know that, when you wear high heels, you can literally dent the floor? (A wooden floor, of course.)

So not only do these things torture your feet, but they also do damage the floor you walk on? Still worth it?

Let's say you're a girl, drag queen, or just a regular guy who enjoys wearing high heels from time to time, and you weigh about 130 pounds. Let's also assume your shoes - regular flats, that is - have a bottom surface area of about 10 square inches. With heels, the bottom surface area that comes in contact with the floor could be half that, or even less.

While you are wearing flats, your shoes push against a large area of the floor and thus the pressure (force per area) is relatively small - about 13 pounds per square inch. However, in heels, you still exert the same force downward due to your weight - just over a smaller surface area. So the pressure would be around 30 pounds per square inch or more.

And what if your heels narrow into a single spike, that takes up only .1 square inches? And then, if you put all your weight on your heels (it's fun to see how long you can balance sometimes, am I right?)? That's 650 pounds per square inch! And if you try balancing on just one heel?! 1300!

So yeah, you get the idea. Wearing heels drastically increases the pressure you put on the floor, which makes it more likely you'll put dents in it or damage it in some way. So if you're looking for an reason to stop wearing them but don't want to admit to the stereotypical cop-out "they make my feet hurt"...try this more creative excuse.

But I'm pretty vertically-challenged as it is, so I think I'll take my chances.

Until next time,

bazinga818
Static electricity is a stationary electric charge that is built up on a material. We might experience static electricity when touching a doorknob or rubbing our feet on the carpet and shocking a friend - sometimes we can even see a spark. This static electricity is formed when we accumulate extra electrons and they are discharged onto another object.

So we know that electrons are tiny negatively charged particles, and protons are tiny (though not nearly as tiny as electrons) positively charged particles. Electrons move around in the outer shell of an atom, while protons and neutrons (neutral charge) reside in the center of the atom.

Sometimes the outer layer (the negatively-charged electrons) of atoms are rubbed off, producing atoms that have a slight positive charge. The object that did the rubbing will accumulate a slight negative charge as it gets extra electrons. During dry weather especially, these excess charges don't dissipate very easily, and you get static electricity.

So here's a good static electricity experiment: rub a balloon on your hair. Some of the electrons from your hair jump to the balloon, giving it a slight negative charge. Now if you put the balloon against a wall, it will stick since the negative charges in the balloon will attract the electrons in the atoms of the wall.

Hope you enjoyed this short blog post and learned something about static electricity!

Until next time,

bazing818
It is often believed that, when turning in a car, you lean the opposite way of the turn. Turn right, you feel a force left. This is a common misconception.

In actuality, as the car turns right, our bodies' inertia (directly proportional to mass) keeps us wanting to travel in a straight line, which is why we feel thrust leftward. This is also why, when we slam on the breaks, our bodies jerk forward - they want to keep going straight.

The above explanation makes sense, but I've always wondered why we didn't feel a force inward in circular motion if the centripetal force points to the center of the circle. So I did some research, and learned some more about it.

An inward net force is required to make a turn in a circle: the centripetal force. In the absence of any net force, an object in motion continues in motion in a straight line at constant speed (Newton's first law: an object in motion stays in motion unless acted upon by an outside force).

In a right-turning car, the passenger slides left. In a sense, the car is beginning to slide out from under the passenger. Once they strike the left door of the car (or their seatbelt holds them in place), the passenger can now turn with the car and experience some circular motion. There is never any outward force exerted upon them. The passenger is either moving straight ahead in the absence of a force or moving along a circular path in the presence of an inward-directed force - the centripetal force.

The car itself is what provides the inward centripetal force, even if we as the passengers don't feel the force directly.

So hopefully that clears up any questions you had about feeling centripetal force. I'd been confused about this concept for over a year now, so researching it definitely helped me understand it better!

Until next time,

bazinga818
Parkour, sometimes referred to as "free-running", has always fascinated me. How do they do it? I for one can't even do the simplest of parkour stunts, but I looked into the physics of it a bit, and thought I'd share what I found.

Of course, these stunts seem scary to us because, frankly, they hurt when we try to do them. Or when I try to do them, anyway. In order to make it hurt less and avoid broken bones - to lessen the impact upon landing after a fall, or to decrease the force upon a set of fingers while grabbing onto a wall - it is essential to reduce the acceleration during each collision as much as possible. This relates to Newton's 2nd Law, of course, as F=ma. Increase the acceleration, decrease the force, as there is an inverse relationship between the two.

To do this, one would increase the time of impact by smoothly bending, flexing, or rolling during impact.

Let's apply some of the physics to an example. During impact with the ground, there are essentially two forces acting on your body -- the downward force of gravity (mg) and the upward force of the ground.
Applying Newton's second law we get:
Fnet = Fground - mg = ma
So let's say that I jump from a height of 3.0 meters onto the ground. How much force is the ground going to exert on me during impact?

First, let's apply conservation of energy to determine my speed just before contact.
The gravitational potential energy (mgh) due to my initial height relative to the ground is going to be converted into kinetic energy (½ mv2) just before landing. So
Mgh = ½ mv2
and v = [2(9.8m/s2)(3.0m)]1/2 = 7.7m/s
Now I have to be brought to a stop.
Fground = m(g + a) = m(9.8 m/s2 + a)

We can see that the force of impact depends on the acceleration. But acceleration = change in velocity/change in time and therefore depends on the time of impact. Therefore, if I land on heels and stay stiff, I could be hurt or break a bone. However, if I land on the ball of my foot and bend my knees or duck into a roll upon impact, the time of impact can be increased dramatically. By decreasing my velocity over this extended period of time, the force is substantially reduced.

So there you have it, the physics of parkour. Now I can go apply this and become a parkour beast. (Or break my neck. Let's hope for the former.)

Please enjoy the awesome parkour video I found below.

Until next time,

bazinga818
So you know those toys where there was a wooden ball attached to a string attached to a wooden handle thing? And you had to swing the ball up and catch it in a ball-shaped indentation on the top of the wooden handle thing? No? Well, maybe a picture will help...

Anyways, it took me awhile to find this picture, as apparently Google has no idea what you're talking about when you search "swing ball on string into indentation" or similar phrases. Finally, I found it's real name - "Cup and ball"...this is probably because many of them look like this instead of the above picture:

Yeah. Anyway, I happened upon this game (mine looks like the first picture) a few days ago hidden in a drawer in my house, and proceeded to play with it for the next 20 minutes...insisting, when my mom began to question my level of productivity, that I was doing homework - physics homework.

So onto the physics part. Of course, when you swing the ball around to land in the cup, the magnitude of tension in the string changes. At the bottom of its path, tension (T) = mg+mv^2/r, as tension and force of gravity(mg, m being the mass of the ball) act in opposite directions. For the top, however, T = mv^2/r - mg, as T and mg both act downward. On the left and right sides of the circular path of the ball, T = mv^2/r as T acts in the horizontal direction and mg in the vertical.

When you try to catch the ball in the socket, you'll notice you can't just hold your hand steady and hope the ball will magically land in the socket - even if you have it perfectly lined up, doing that will just make the ball bounce back out. In order to catch the ball, you have to lower your arm as the ball lands in the cup, cushioning the impact - similar to how you would bend your knees when landing on your feet from a jump.

Doing this increases the time of impact, decreasing the acceleration of the ball as it falls into the cup. This in turn decreases the force on the ball, allowing it to stay in the cup or socket. Another example of this is your car's airbag - when in a crash, your airbag increases the time of impact, decreasing your acceleration and thus decreasing the force on you.

So there you have it, the physics of the ball-and-cup game. I miss these childhood simplicities that could entertain for hours. Hope you enjoyed!

Until next time,

bazinga818
Since we're learning about rotational kinetmatics and such in class, I thought it would be a good idea to stick to circular motion.

So, carousels. Since we know that velocity equals distance over time, obviously the longer the distance the longer it would take to reach the destination. Carousel horses, though they may look like they're all moving at the same velocity, actually have different linear velocities depending on how far they are from the center of the carousel.

The more you think about it, the more it makes sense: horses on the outside have a longer distance to cover as the circumference of the outside of the carousel is bigger than any other inside horses' paths. So as the carousel spins, the horses on the outside have to maintain a faster linear velocity than the inside horses because they are covering more distance.

This concept, of course, we all learned or at least understood on some level from taking Physics B. Now that we're in Physics C, however, we can obseve the angular velocity. Whereas linear velocity is the change in distance over time, angular velocity is, as its name suggests, the change in the angle (theta) over time.

Though, in the carousel example, a horse close to the center has a slower linear velocity than a horse on the outside...each horses' angular change with respect to their starting positions is the same as the other horse! They'll both cover the same rotation in the same period of time. So we see, while linear velocity on a carousel depends on the horse's distance from the center, angular velocity remains constant for all horses.

bazinga818
Yay for more circular motion! So does anyone know what I'm talking about when I say "playground spinny things"? There like mini merry go rounds for playgrounds, but like...without the animals and cheesy music. Someone goes on them and you spin them really fast? There are funny fail videos on the internet of people spinning super fast on them and then flying off? Sound familiar?

I hope so, because I really don't know what they're called. But anyway, I thought I'd talk about the physics behind them for a bit.

So when you spin on these spinny things, you feel a centripetal force (Fc) and centripetal acceleration (ac) point towards the center of the circle. The centripetal force, Fc, is equal to mv2/r, and remembering Newton's 2nd Law (F=ma), we can then deduce that ac = v2/r.

If, like the people in those fail videos, you were to spin so fast that you flew off the spinny things - you would fly off in a path tangent to the circle. This is because your velocity acts tangently to the circle.

There's something I don't quite get about this, though. When you spin, you feel like you're being pulled outward away from the center of the circle...if Fc is pointed toward the center of the circle, why do you feel a force outward instead? Maybe I'm just thinking about it wrong, but either way it'd be great if someone could explain that to me.

Thanks for reading! I hope you enjoyed a snippet of the physics behind those playground spinny things I still don't know the name of.

Until next time,
bazinga818

EDIT: I guess they're actually called merry-go-rounds too? Weird. Anyway, I found a nice fail-compilation video for you to enjoy below. For some reason people seem to think it's a super awesome and profoundly intelligent idea to take a motorcycle wheel to these things...makes for a good video anyway! Yay circular motion!

My favorite is probably the one at 1:23...that kid just goes downnnn, man. Like come on it wasn't even going that fast. What a pansy.
And I really realllllly want to try the one at 1:51, minus the faceplant part.
I also thoroughly enjoy the duck one.
We've all experienced it. You're walking in the hallway, the not-so-trafically-ideal hallway (we really need to invest in a double yellow line down the middle so everyone walks the right way...), and suddenly you and a stranger come face to face. You awkwardly try to maneuver around eachother, both stepping the same way...twice. I find myself in these situations daily, so I thought it'd be cool to think about the physics behind it.

As you walk forward, you have a forward momentum of mv; m being your mass, v being the velocity at which you're walking. When you and another person are walking towards eachother, you must apply a force down and at an angle that pushes you backwards, so as to stop your forward velocity and thus momentum. As you apply a force down on the ground, the ground also pushes up on your feet because, according to this guy Newton, for every action there is an equal and opposite reaction.

Depending on how long you apply the force, you will have a certain impulse which will inevitably change your velocity. Your impulse will equal the average force you exert on the ground multiplied by the duration of time during which you apply the force (J = Ft).

As the two of you sidestep eachother - laughing nervously, trying to avoid eye contact - you exert different forces down at different angles to propel you left or right. Finally, after what seems like an eternity, you both agree on a side and proceed past each other. As you begin forward again, your feet apply an increasing downward force on the ground, causing you to accelerate back up to your initial velocity before this awkward encounter.

So, there you have it: the physics of uncomfortable hallway run-ins with strangers. Next time this happens to you, think of this blog post and I hope you'll feel less awkward! More likely not, though. Either way, I hope you enjoyed!

Until next time,
bazinga818
So I figured it was time I do a sports post, since it seems to be a super popular blog topic recently and I can't think of anything else to do at the moment. Time for the physics of volleyball!

Jumping right into it (haha volleyball puns ), I'll start off with the serving part. So when you serve the ball over the net, it becomes a projectile whose distance is dictated by the force at which you hit it. Assuming there is no initial vertical velocity and you hit the ball straight over the net, you can find the initial velocity by timing how long it takes for the ball to hit the ground (though that shouldn't happen in an actual game...) and measuring the distance it traveled.

You could use the kinematics equation x = Vot + .5at^2 to find the initial horizontal velocity, which would also be the final horizontal velocity since a = 0. Then you could use the equation Vf = Vo + at to find the final vertical velocity for the ball, as you know the acceleration due to gravity is -9.8m/s and the initial vertical velocity is 0.

Another physics-related concept in volleyball involves diving for the ball. When you dive to the side or forward for a dig, you exert a force down on the ground at an angle to push you in that direction. Since volleyball is a fast-paced sport and involves split-second decisions and actions, you would have less than a second to recognize where the ball was going and exert this force. But the force would have to be large enough to propel you to the ball; so you would exert a force of great magnitude over a very small amount of time. This would be your impulse: average force times time, or Ft.

So those are just a few of the physics concepts related to volleyball! Hope you enjoyed!

Until next time,
bazinga818
So these past two weeks we've been doing an independent unit on momentum, and I just thought I'd share my thoughts on it.

On some level, I like the independence of this unit: going at my own pace, picking what I want to do each day, doing stuff in whatever order I want, working with other people, etc. It's nice not to have a structured class period every day, and I like learning at my own pace.

But then again, there are definitely aspects of this unit I'm not fond of. For example, I really hate reading textbooks to learn stuff for science and math concepts; I often have a hard time comprehending the information. It's one thing to learn the info in class and then just do practice problems in the textbook, but to learn the info in the textbook first - I find it very difficult. Sometimes it's because I zone out and have to reread stuff, but frequently it's just because I simply don't understand what I'm reading and have to reread or try practice problems step by step.

Aside from that, I'm grateful that I feel mostly comfortable with this unit already from last year - I just have to work on finding the center of mass and mastering 2D momentum problems, along with a few other (hopefully minor) things. I'm liking the Walter Lewin videos and finding them very helpful - I enjoy his teaching style. And even though it's a lot of work, I know I'll definitely benefit from the webassign and all the MC and practice problems in the IU packet! Let's hope this test on Tuesday goes well

Until next time,
bazinga818
So I figured I'd write a blog about my experience in building my first ever catapult! Though it was definitely intimidating at first, I found the project actually turned out to be a lot of fun to build and launch.

My group settled on a trebuchet design, and after working out the ideal angles, sizes and overall plan, we got to building. We built for 2 days, just about 3-4 hours a day. I won't bore you with the cutting and sizing and drilling of wood, because I think we all know that's not exactly the most fun part of the experience. Once we got our catapult mostly built, we began our test trials. Surprisingly, the ball actually went up in the air the first trial! Granted, it was the wrong way...but psh, details.

We did trial after trial, finding minor errors and fixing them; the ropes for the sling were too long, the pouch to put the ball in was too flimsy, the pin didn't stay on long enough or wasn't at the right angle, the throwing arm wasn't totally straight. Now that the preliminary building was over, I actually found it fun to be able to help isolate the different issues with our catapult and figure out how to fix them to make it launch better.

Finally, success....our catapult launched the right way! Tweaking a few more things, we were able to launch a small rubber ball slightly bigger than a softball about 80ft. It was so cool that we had literally just started with some wood, power tools and a design and now we were launching up to 80ft! We decided that was sufficient and left it there, to be launched again that Friday on launch day.

Due to unfavorable conditions (aka LOTS of wind), we had some trouble setting up (and keeping upright) our catapult; however, we still managed to launch 3 trials (though the last one was a bust), our longest distance at 27 yds. Our catapult launched diagonally, however...so if you ask me, I'd say it was longer than 27 yds.

I should probably talk a little about the physics behind the catapult. We put weights on the front of our throwing beam, and when let go the force from the weights brought one side of the beam down and the other side - the side where the sling was attached - up where the softball would release from its pouch. When it released depended on the angle of our pin where the ropes from our sling were attached.

And of course, we all (should) know our kinematics equations. The ball released at a certain horizontal and vertical initial velocity, and by timing how long it was in the air and measuring the distance it travelled horizontally we could figure out these velocities (x = Vot + .5at^2).

Though it wasn't a good day to launch catapults, I still had fun with the project and enjoyed building it and seeing our result. Catapults are pretty awesome.

Until next time,

bazinga818
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