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. Thanks for reading, 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.

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

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 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

Another thing to think about is that while your mass and the force of gravity is pulling you down, the force of drag or air resistance is pushing you up. Awesome post!

Nice post...physics really is everywhere!

Hahaha this is an awesome post! I never thought about the physics in trick or treating...pretty cool! It makes me nostalgic for the trick or treating I did when I was younger. I miss Halloween already!

This is so awesome! It's been forever since I watched the Ice Princess and it's really cool to actually understand the physics they're talking about in the scene! Great post!

I love zip lining! Nice analysis of the physics behind it. Cool post

Never thought about golf physics before. Nice post!

I feel your pain man.

Yeah, my mind is definitely blown. Awesome blog post!

I never thought about the physics of trampolines before! Awesome post.

I had a lot of fun with the catapult too! It was difficult but such an awesome experience.

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

I'm guessing most of you were intrigued and confused by the title, so let me explain. You know how when you eat cereal, the pieces of cereal in the milk start to clump together? So when you're nearing the end of your bowl of Cheerios, there are often several clumps of two or three cheerios stuck together, all floating around. Why does this happen, you ask? Well, it all has to do with surface tension. Because water molecules in the milk are attracted to glass, the milk around the edges of your cereal bowl curve up slightly, creating a concave in the middle of the milk. This is why your cheerios not only stick to each other, but often cling to the sides of the bowl as well - they float up along the curve. Also as a result of surface tension, each piece of cereal creates its own little dip in the milk's surface while it floats around. When two pieces near each other, their dents combine to make one big dent and they stick together! Cool right? Now if only the last few clumps could stay still instead of swirling away when I try to capture them with my spoon. #cerealprobz. Amiright? So there you have it, the physics behind cereal-sticking. I hope you enjoyed this blog post, and until next time,

As much as I'd like to tell you I've figured out all the physics of being invisible and how to acquire it as a superpower, I would be lying. To add insult to injury, this post isn't even about the physics of invisibility, but rather about why true invisibility is an impossibility due to the laws of physics. So if you don't want all your dreams of becoming a superhero with powers of invisibility to be crushed, it would be advisible to stop reading here! To everyone sticking around, be prepared to have your mind blown. To be truly invisible is to have light pass through you. You are still a solid being, but no one can see you because light passes through you rather than reflecting off of you. So as not to freak passersby out, it's assumed you would have to be naked pretty much all the time, and never carry anything on you - otherwise people would see floating clothes and objects. Naked outside in the middle of winter? And if it rains, the drops would bounce off of you, making your outline visible. This would happen eventually just with dust particles that collect on your skin too. Not to mention constantly having to dodge people and making sure you don't get run over by cars. Sounds fun so far. So, now on the physics mind-blowing part. What do you think the world would look like if you were invisible? The answer? Nothing. You see things because light bounces off of them and reflects in your eyes, right? That's why we can't see in the dark; there's no light. Well, if you were invisible, by definition light would pass through you - so images couldn't be reflected in your retinas for your brain to interpret and turn right-side up. I deeply apologize if I have ruined any of your fantasies, reader. But, if invisibility were a possibility, you wouldn't be able to see anything or anyone any more than they could see you. You would be blind. Trust me - I wasn't happy about it either. To those of you who are impartial to the subject of superpowers, I hope you enjoyed this blog post! Thanks for reading, and until next time:

Hi again, here to talk a little about the physics behind roller coasters! Something you might not know, or maybe you knew it on some level but never really thought about it - roller coasters aren't propelled along the ups and downs of the ride - they don't use an engine. They're only pulled to the top of the first hill; in order to get through the rest, the carts have to have enough forward momentum to get over the hills and/or through the loops. It all depends on the conversion of kinetic energy to potential energy and vice versa. Potential energy, given by the equation Pe = mgh, is at a maximum when the roller coaster is at the top of a hill, since it's height is the greatest. As it starts traveling down the hill, it's Pe is transfered into kinetic energy (Ke), given by (1/2)mv^2. Kinetic energy is at its maximum at the bottom of the hill because this is where it has its highest velocity, high enough to get the roller coaster up and over the next hill. In turn, then, the roller coaster's hills must be high enough to allow for a fast enough velocity when the cart reaches the bottom in order to get it over the next hill. Of course, it would make sense then that when Ke is at its maximum, Pe is at its minimum and vice versa. Crazy, right? Physics is bomb. You might be wondering how the ride runs smoothly without an engine on the cart, and how it stops when you get to the end (or rather, the beginning) of the track. Well, the wheels offer a lot of help - there are three sets of them. Running wheels guide the coaster on the track, friction wheels control lateral motion (movement to either side of the track), and a final set of wheels keeps the coaster on the track even if it's inverted. Compressed air brakes are what stop the car as the ride ends. So there's a bit about the physics behind roller coasters! If this blog post freaked you out a little when you realized roller coasters don't actually have an engine and we're basically on our own in the cart from beginning to end, don't worry. Riding roller coasters is actually more safe than most regular activities, like playing sports or riding your bike. The engineers that design them and the Amusement park owners who hire these engineers make sure of that - otherwise they'd be in for some pretty serious lawsuits. Thanks for reading! Until next time,

Nevermind, got it.

Can anyone help me with how to start 16? If the plane is flying horizontally, does the Vy initial = 0?

Hello, world of AP Physics C. I'd like to talk to you about the physics of swings today. Swingsets involve circular motion! If you think about it, when you swing you're actually completing a half circle each time you swing to and from your highest points. At your lowest point (the bottom of the circle), the tension (T) from the chains is pulling upwards, and your weight (mg) is pulling downwards. The centripetal acceleration (v^2/r), as well as the centripetal force (mv^2/r, using Newtons Law F=ma) both point towards the center of the circle. Therefore, to find the tension at the bottom of the circle, one would use the equation T=(mv^2/r) + mg. At either side of the circle, since tension and Fc point inward and weight is downward, the equation would be T=mv^2/r. If you had a great enough velocity (which points tangentally to the circle, perpendicular to the Fc and ac (cent. accel.)), you might be able to swing all the way around the top of the swingset. For this to happen, the tension would have to be a minimum of zero newtons. At the top of the circle, since both tension and weight point downward (as well as Fc), the equation to find tension would be T=(mv^2/r) - mg. Now you know about the physics of swingsets! I've included a few pictures below to further your comprehension, if my explanations weren't explanatory enough. Thanks for reading, see ya next week! bazinga818 http://www.ic.sunysb.edu/Class/phy141md/lib/exe/fetch.php?media=phy141:lectures:ballonstring.png

Nevermind got it haha it's too late I can't do proper math

Where did your .5 go when you substituted x=.5(Vo+Vf)*T to get 618=VxT?