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Blog Entries posted by AlphaGeek

  1. AlphaGeek
    {I added a second cookie Q to buy you guys more time. Hopefully Charlie won't answer both before someone else in the class answers one..}

    You are a Kerbal physicist for Kow Jumperd Over the Mun, a company that excels in anything spacey or astronaut-y. After ending an argument between two colleagues, you decide to take a lunch break. The cafeteria guy, Louie Eeloo, has a thing for riddles, which started out amusing and grew annoying as the years passed. You were hoping that the line would be long and Louie would be busy, seeing as how its Flungus day in the small cafe (who doesn't love a heaping plate of Flungus?). No such luck. The cafe is a ghost town. You turn to avoid Louie and order out, but he's already spotted his next victim.
    Louie offers Ooglie Cookies to all riddle solvers. Because you have nothing better to do until the next launch, you decide to humor him.

    Louie says, "I have four friends, we run 'round Jool happy as can be. A 50 kg Kerbal on Kerbin weighs 3 kg on me. What am I?"

    Your stumach grumbles. You could really go for an Ooglie right now. What's the answer to Mr. Eeloo's riddle?

    It's actually not the day of the dead. I just like this photo. Have a feliz day anyway

  2. AlphaGeek
    Soooo, because this is my last blog post for this year ( ), I thought it would be fitting to do a course reflection on the AP-C physics class this year. I thought I'd do it in a "bests-vs-worsts" top 5 format, kind of like you could find on collegeprowler.com when viewing different schools.

    Top 5 Bests:

    5.) Blog Posting [i thought this was really fun! I've never done anything like this before for a class. It brought up interesting physics applications and I thought it was fun to converse with classmates on the site ]
    4.) Independent Units [As uncomfortable as I was at first, independent units forced me to manage my time, work harder than usual to learn the topic, and was great preparation for college. I feel like everyone sould experience this kind of a unit before graduating]
    3.) Assigned practice problems from the readings [Assigned problems were REALLY helpful. I would've struggled a lot more than I did had I skipped doing the sample problems]
    2.) Units with Lecture & book follow-up [This is my favorite way to learn things! The read-then-lecture method]
    1.) VIDEOS <3 [Hands down the most helpful resource in Physics]

    Top 5 Worsts:
    ...I think this is my biggest beef. I really don't have 5 things to complain about.
    1.) Readings weren't assigned [When life gets busy in the middle of the year, especially with a number of APs, sports, etc., readings are the first thing to get cut out for me if they're not assigned. Confession: when the going got tough, I would often skim or not read. I reccomend assigning readings in the future. Kids will complain, but they'll thank you when they see better grades and their AP score.]

    Overall, this was a successful year. A note to future students: This is by far the hardest AP course I've taken throughout high school. If you want to succeed, you must:

    A.) Read the textbook and do some practice problems
    B.) WATCH THE VIDEOS. Whether you're confused or simply want review, these are soooo outrageously helpful. It's like being in class a second time, except in 15 minutes or less instead of 42. Plus, you can skip over any sections that you feel you know solid.
    C.) REVIEW THE EQUATIONS AND FREE RESPONSE BEFORE THE AP. I went through most of the E&M free response questions as well as both E&M and mechanics equations before the exam. KNOW THE EQUATIONS! I swear equations and key concepts are the majority of the test when it comes to the multiple choice Qs.

    Any favorite parts of the year? Things you wanted to change? Post below with your opinion!

    ...I can't believe we only have 1 more day of physics
  3. AlphaGeek

    So. I was thinking of what to carve on my pumpkin earlier and thought, "What's something that'll scare the pants off of anyone, even high schoolers?" Bingo, air resistance. Many of us were shaking in our boots when Mr. Fullerton derived a few drag-related equations, but looking back they're not too bad right?

    Here's a little review. That long page really boils down to a few key equations:

    Air resistance = Fdrag = bv = cv2 , where b and c are constants
    VT= (mg)/b
    V = VT ( 1 - e(-b/m) )
    V = (mg/b)( 1 - e(-b/m) )
    a = g e(-b/m)t

    Some equations may contain the variable tau, which looks like a backwards J or a T with a tail. I will use T to represent tau. It is a time constant that can be substituted into the equations above. Tau = T = m/b.

    I hope that helped a little. Sleep with the lights on tonight, folks. 'Tis the season!
  4. AlphaGeek
    PRESSURE'S ON: First person to answer this correctly gets a cookie. :eagerness:

    You're at the playground with a girl you babysit, little Tori McTorque. Being 9 years old and devious, Tori took you wallet and threatened to spend your babysitting money on ice cream and root beer. Kids these days! You chased her over to the see saw, where she and her friend (Lil' Newton) sat happily on one side. You have to think of a way out of this! You don't want all of your hard-earned cash to go to waste, do you? Because physics is always the answer, you decide to make a bet with the little devils.

    You propose to Tori that, if you can make the see saw balance with three people on it on your first try, she must give back the wallet. If you fail, Tori will get unlimited ice cream privileges! D:

    Knowing off the top of your head that the average weight of 9 year old children is roughly 28 kg and that Tori and Newton are sitting 1 m and .7 m away from the center of the see saw, how far should you place a 61 kg teenager with a mullet from the pivot point?

  5. AlphaGeek
    A friend returned from training for the air force and told me about some of the crazy things that he and his comrades would do to pass the time. Some of these included taping each other to the ceiling and human-drawn chariot races, but one of the most messy and fun instances he described was a hallway slip n' slide. True story: he and his hall mates put towels to the bottom of their sleeping quarter doorways, filled the hall with soap and water and proceeded to slide down the hallway as though it were a seabreeze water slide.

    Let's say the hallway is 15 meters long, and each cadet gets a 8 meter running start before diving down for a slide. If one guy sprints and reaches a speed of 4 m/s before flopping into the suds (which has a coeff. of friction of .2), does the cadet slam into the other side of the hallway or get soapy bragging rights?

    ...In terms of the cookie question, Charlie: 2; entire rest of the class: 0. Come on, guys! (Nice job Charlie)

    Good luck! --Alpha Geek

    DISCLAIMER: It's unlikely that this exact situation with such distance in the slide will occur. The coefficient of friction with the floor and the speed of the person are strictly for cookie-question fun, not actual values. In other words, don't try this in your living room!
  6. AlphaGeek
    Hi everybody!

    I haven't done a cookie problem in a while, so here it goes! The problem is related to the current unit. First correct answer gets a cookie. I think Charlie is the only one who answers these things, but I enjoy writing them and he likes cookies, so... It all works out :glee:

    Slinky the dog is bored (since Andy is off at college and all), so he decides to watch Walter Lewin's video Lecture 15. Slink thinks the solenoid example is really cool and decides to try it out himself. If he hooks his middle into a circuit of 1A and stands with his front feet .5 m away from his back feet, what is the magnetic field inside of Slinky? Note: Slinky's center is composed of 100 turns, and each turn is uniformly spaced.

    I love Disney! Bonus question: What is the name of the arcade in Toy Story?

    Have fun!

    --Alpha Geek
  7. AlphaGeek
    *yawn* It's a beautiful Tuesday morning and you've awoken from camping in the jagged pass. You stow your tent into the key items pocket and continue on your trek to Lavaridge Town. You're on your merry way, thinking fondly of a dip in the hot springs, when the grass in front of you begins to rustle!

    Oh my, a Spoink appeared! Adrenaline pulses through your veins as you shout, "Go, McNugget!" (Mc.Nugget is none other than your lvl 98 torchic).

    You quickly break out your pokedex, which informs you that a spoink's tail can stretch up to .3 m from when it rests at equilibrium. You also remember hearing from a passing hiker that it's angular velocity between attacks is 6 rad/sec. Due to torchic's smaller size, it can only use scratch when spoink is closest to the ground. Asuming that torchic can strike as soon as you order him to attack, how soon after spoink starts oscillating from equilibrium position (moving up first, then down) should you tell torchic to use scratch?

    ...And for those of you who wonder why you didn't delete scratch for a cooler move, I think scratch is the bomb.
    Respond now, a cookie is on the line! (This one is larger than the one awarded from the first challenge )

    --The Geek
  8. AlphaGeek
    Often times, values in physics are abbreviated using metric prefixes, or SI prefixes. I found this table the other night and thought it would be helpful to post, in that I'm sure I'm not the only one who gets these mixed up sometimes.

    Thanks to wiki for this table:

    [TABLE="class: wikitable, width: 0"]
    [TH="bgcolor: #CCCCFF, colspan: 2"]Metric prefixes[/TH]
    [TH="bgcolor: #EEDDFF"]Prefix[/TH]
    [TH="bgcolor: #EEDDFF"]Symbol[/TH]
    [TH="bgcolor: #EEDDFF"]1000m[/TH]
    [TH="bgcolor: #EEDDFF"]10n[/TH]
    [TH="bgcolor: #EEDDFF"]Decimal[/TH]
    [TH="bgcolor: #EEDDFF"]Short scale[/TH]
    [TH="bgcolor: #EEDDFF"]Long scale[/TH]
    [TH="bgcolor: #EEDDFF"]Since[n 1][/TH]
    [TD="align: center"]Y[/TD]
    [TD="align: right"]1000000000000000000000000[/TD]
    [TD="align: center"]Z[/TD]
    [TD="align: right"]1000000000000000000000[/TD]
    [TD="align: center"]E[/TD]
    [TD="align: right"]1000000000000000000[/TD]
    [TD="align: center"]P[/TD]
    [TD="align: right"]1000000000000000[/TD]
    [TD="align: center"]T[/TD]
    [TD="align: right"]1000000000000[/TD]
    [TD="align: center"]G[/TD]
    [TD="align: right"]1000000000[/TD]
    [TD="align: center"]M[/TD]
    [TD="align: right"]1000000[/TD]
    [TD="colspan: 2, align: center"]million[/TD]
    [TD="align: center"]k[/TD]
    [TD="align: right"]1000[/TD]
    [TD="colspan: 2, align: center"]thousand[/TD]
    [TD="align: center"]h[/TD]
    [TD="align: right"]100[/TD]
    [TD="colspan: 2, align: center"]hundred[/TD]
    [TD="align: center"]da[/TD]
    [TD="align: right"]10[/TD]
    [TD="colspan: 2, align: center"]ten[/TD]
    [TR="bgcolor: #EEEEEE"]
    [TD="colspan: 2"][/TD]
    [TD="align: center"]1[/TD]
    [TD="colspan: 2, align: center"]one[/TD]
    [TD="align: center"]d[/TD]
    [TD="align: left"]0.1[/TD]
    [TD="colspan: 2, align: center"]tenth[/TD]
    [TD="align: center"]c[/TD]
    [TD="align: left"]0.01[/TD]
    [TD="colspan: 2, align: center"]hundredth[/TD]
    [TD="align: center"]m[/TD]
    [TD="align: left"]0.001[/TD]
    [TD="colspan: 2, align: center"]thousandth[/TD]
    [TD="align: center"]μ[/TD]
    [TD="align: left"]0.000001[/TD]
    [TD="colspan: 2, align: center"]millionth[/TD]
    [TD="align: center"]n[/TD]
    [TD="align: left"]0.000000001[/TD]
    [TD="align: center"]p[/TD]
    [TD="align: left"]0.000000000001[/TD]
    [TD="align: center"]f[/TD]
    [TD="align: left"]0.000000000000001[/TD]
    [TD="align: center"]a[/TD]
    [TD="align: left"]0.000000000000000001[/TD]
    [TD="align: center"]z[/TD]
    [TD="align: left"]0.000000000000000000001[/TD]
    [TD="align: center"]y[/TD]
    [TD="align: left"]0.000000000000000000000001[/TD]
    [TD="bgcolor: #EEEEEE, colspan: 8"]

    ^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.


    These prefixes were developed to shorten extremely large or small values, such as the teeny tiny mass of an electron (9.11 E -31 kg, or .000911 yg) in contrast to the very large Avogadro's number (6.022E23 atoms, or .6022 yotta atoms in one mole). When tacked onto constants, sometimes we don't realize just how intense these prefixes really are. Here are a few examples to help grasp the largeness and smallness of these constants:

    1. The Earth weighs 5,972 yotta grams, or 5.972E24 kg. It would take over 850 quintillion elephants to match this weight, or just over 81 moons.

    2. The average mass of a human cell is 950 femto grams, or 9.5E-13 g. If you cut a penny into a trillion pieces of equal mass, the human cell would still have a lower mass than the penny bit. AND you would get arrested for defacing US currency. It's simply a lose-lose situation.

    3. On earth, there are an estimated 7.059 G people (or 7.059 billion people). This is roughly 1000 times the number of pigeons in NYC. However, this is roughly 1/3 of the amount of hotdogs Americans consume in a year. (Yes really-- Americans chow down on an estimated 20 billion a year. That's about 70 hot dogs per person).

    Hope that was enlightening if not helpful!

    --Alpha Geek
  9. AlphaGeek
    Family Guy isn't exactly school appropriate in most cases, but it is, however, physics appropriate. In one episode, Brian (the dog) educates Peter (the tubby man) on his weight issue. Brian claims that Peter has his own gravitational pull, and continues to demonstrate this by placing an apple nearby his stomach. The fruit then assumes orbit directed around Peter's abdomen.

    ...For those of you who are not familliar with the episode, here is a not-so-legally posted, poor quality youtube video featuring our obese friend. :apple:


    Lets take a closer look at the physics of this cartoon.

    Assuming that a feasible weight for roughly 44 year old Peter is 100 kg (220 pounds) and the average apple weights .15 kg, as well as the radius of the orbit being roughly 1 meter from Peter's center, here are the technicalities of the situation.

    The force of gravity on the apple = (GmM)/r2 = ((6.67E-11)(100*.15)/12 = 1E-9 N

    The acceleration due to gravity on planet Peter is = ((6.67E-11)(100))/12 = 6.67E-9 m/s2

    And finally, for the apple to escape its orbit around Peter, it would have to be going a grand total of [(2GM)/r]1/2
    , or 1.15E-4 m/s.

    Note how these values are extremely small. For one thing, this situation is impossible in the first place. To emphasize this, the gravitational force is so small that it likely could not even pick up the apple. Even if it were magically strong enough to do so, the speed of the apple was far greater in the video than its small escape velocity, and would fling out of orbit before Brian even turned on the Three Stooges. Sorry, Seth McFarlane. Physics disagrees with you. Guess Family Guy isn't such intelligent programming after all...

    --Alpha Geek
  10. AlphaGeek
    It snowed a little again today, which put me in the mood for some winter-related physics. :snowman: Some of you may be familiar with the movie "National Lampoons Christmas Vacation," a very silly yet amusing film about the holiday antics of the Griswold family. During one scene, Clark Griswold takes his brother and the children to go sledding. He decided to spray the bottom of his sled with a kitchen lubricant, significantly decreasing the friction between his sled and the snow.

    For those of you that have never seen this clip before, skip to 1:20 for the sled action (before that is all the brother talking, he's kind of loopy).

    So how much does greasing up an object truly effect friction?

    Between two metals (lets use two hunks of aluminum for example), the coefficient of friction is roughly 1.05 to 1.35. When greased however, mu drops down to .3, which is anywhere from a third to a fourth of the original coefficient. The same goes for the coefficient of friction between snow and Clark's steel sled. The coefficient of friction between snow and steel is roughly .1. The Griswolds were sledding at night, so if the snow turned to ice the coefficient would be remarkably lower: 0.015. Add some canola or olive oil spray to the mix, and friction would be extremely small.

    In other words, next time you break out the toboggan for some serious sled races, make sure to pack the pam!

    P.S. I didn't pull those numbers out of a hat, my main source is http://www.engineeringtoolbox.com/friction-coefficients-d_778.html. Thanks, google!
  11. AlphaGeek
    Hi everyone, just figured that I'd post an accumulation of what I've been studying for the test tomorrow morning. It goes in video order because that's the order that I learned the material in. If something is too vague, I reccomed looking at the video for elaboration


    Current and Current Density
    Resistors and Resistance
    Voltmeters and Ammeters
    Ideal and Real Batteries
    RC Circuits: Steady State
    RC Circuits: Transient Analysis (Charging)
    Current and Current Density:

    Current measured in Amps, or charge per sec.
    An electric field is applied to a conductor and a small field is created that opposes it
    Avg. Velocity of electrons in that field= drift velocity (Vd)
    Vol= Bh = Vd * change in time * Area
    # electrons = Volume * volume density(AKA "N")= N *change in time* Vd * Area
    I= N*q*Vd *A
    Current density = J* N*q*Vd
    I= integral (J * dA)
    J= I/A

    Resistance ("Howdy, Y'all!" made my day in that vid, btw)
    p = row =resistivity
    R= pL/A
    V= IpL/A
    E=energy=V/L = p (I/A) = pJ
    I= dQ/dt


    Series: Req= R1 +R2...
    Parallel: 1/Req= 1/R1 +1/R2....
    Kirchhoff's Current Law= sum all current entering = sum all current exiting (conserv. charge)
    Kirchhoff's Voltage Law= sum of all potential drops in a closed loop of a circuit = 0 (conserv. energy)

    Voltmeters and Ammeters:

    Voltmeters: measures v between two points, high resistance, connected in parallel
    Ammeters: measures current, low resistance, connected in series

    Ideal and Real Batteries:

    Ideal: no internal resistance
    V battery = Emf = change in V

    Real: has internal resistance
    V battery = change in V = IR = Emf- (I)®, where r = internal resistance

    For battery:
    W= change in Q * Emf
    P= W/change in time = (change in Q)(Emf)/(change in time)
    P resistor (works for both external and internal) = I2R

    RC Steady State:
    series: 1/Ceq= 1/C1 + 1/C2 ...
    Parallel: Ceq = C1+C2...

    RC Charging:
    W= I2R
    U=1/2 C V2

    Time constant Tao=RC, occurs when quantity is 63% of its final value. 5 Tao= 99% final value (practically final value)

    Note: an uncharged capacitor acts like a wire, a charged capacitor acts like a gap in the circuit (AKA no current)

    ...Okay, bed time. Good luck tomorrow, everyone!
  12. AlphaGeek
    ...Or in coloquial terms, "My stars, is that ctenophore exhibiting bioluminescence?"

    You might think that's all glow, but there's more to this jelly's luster. Bioluminescence occurs when a living organism's cells emit light. Common examples include fireflies and angler fish, who use light to find mates and attract prey respectively. These organisms convert chemical energy into light energy, just as a human body would convert chemical energy (like glucose) into mechanical or heat energy.

    The above jelly fish Mertensia ovum, also known as the Arctic Comb Jelly or Sea Nut, does emit a small amount of blue and purple light. However, those fancy-dancey rainbow colored adornments on its side are actually caused by-- yep, you guessed it-- thin film interference. Sound familiar (think AP-?

    Like light being "bent" into it's different rays of color on an oil spill or in a rainbow, the jelly fish has eight columns of cilia that have a similar effect. Besides their fashionable apearence, the cilia columns or "comb rows" also allow the jellyfish to move as well as sense changes in it's surroundings as would a bug's antenna.

    ...On a less-sciencey note, I found this bubble very enjoyable.

    --AlphaGeek :tyrannosaurus:
  13. AlphaGeek
    Recently, a friend has confessed to me that he has been diagnosed with stage one senioritis. We've all heard of this virus: common symptoms include drowsiness, in-class headaches, increased social tendencies, and worst of all, characteristic decreases in effort and GPA. Though some have better immune systems than others, this sickness is in fact contagious and most seniors contract a mild case. Because knowledge is the number one prevention factor, I intend to explain--using science and graphical representation-- what is known about this common yet dangerous disease. For those of you who seek protection (at least until the end of AP week), please read on.

    Diagnosis: How do I know if I have Senioritis?

    Illnesses ending in -itis indicate irritation and inflammation. Senioritis specifically refers to inflammation of the "give-a-care" gland, and inflammation seems to increase as the temperature rises outdoors. Senioritis is most common in ages 16-18, however some people are simply born with it. In this case, the illness is refered to as "chronic procrastination," an entirely different animal.

    Though little is known about the causes of Senioritis, there are key variables that contribute to the intensity of the illness. Inflammation level of the GAC gland (I) is directly proportional to t, the amount of time (in hours) left until the end of the year. It can be represented by the equation

    I = (2 π t2 P h) /f3

    P= the constant of procrastination. This constant varies, dependent upon personality type.
    t = time (in hours) left until graduation
    f= the number of friends infected
    h= the amount of homework (in kg) the student is assigned each night.

    For a student with a moderate course load and average amount of friends, the constant of procrastination tends to triple after AP week due to a weaker mentality.

    Observe the below graph exhibiting the relationship between academic wellness over time. The decreasing trends are due to GAC flareups, a common side-effect of senioritis. Students with a high P constant are especially susceptible to the virus. Note how in students with relatively high tendencies of procrastination, the AP period provides a brief spike of academic rigorousness, followed by a devastating relapse. We call this spike of functionality "cramming."


    Cures and Coping Techniques:

    ​1.) Senioritis is highly contagious, like influenza or ring worm. Try surrounding yourself by people with relatively low P constants to avoid infection.

    2.) Create mini-deadlines for assignments as well as allotted time to study. Handling work in small bits reduces the chance of GAC flareups

    3.) Wash your hands before eating finger food.

    4.) Try self-medication: remind yourself that senior year is almost over, and in order to do well on APs you'll only have to fight the -itis a little longer. Stay strong, it's the final stretch!

    Bueno suerte!
    --Alpha Geek
  14. AlphaGeek
    As Goalkeeper0 and Mr. Fullerton suggested, I decided to give the soap-and-water approach to understanding flux a shot. If you'd like to try this experiment but can't find one of those ancient metal coat hangers, here's a different approach:
    >>>Credit to Goalkeeper0<<<

    I bent a coat hanger into a solenoid with 5(ish) loops and filled the dish basin in our sink with soapy water. I'm not sure if it's because here wasn't enough soap in the water or a different factor, but the darn soap layer kept popping before I could pull the hanger completely out of the basin. Here's low quality evidence of my findings;

    ...Again, you really can't see much in the picture. I recommend doing the experiment yourself. To give you a better idea of what the soap spiral looked like, it resembled the shape of fusilli pasta. EX:

    Yum. Love the stuff

    Again, this shape is meant to demonstrate how the number of N turns in a solenoid effect the flux. The more loops in the coat hanger, the more bubble-surface there is in our solenoid. This helps reinforce the equation Mag. Flux = BANcos, with B= Mag. field, A= area and N= number of turns in the solenoid.

  15. AlphaGeek
    Ever wonder why studying hard or taking multiple AP tests in a row makes you exhausted, or even hungry? This is because when you think, your brain has to work hard to send "messages" through the neurons to different parts of the brain and body. Cellular respiration turns your food (glucose) into adenoside triphosphate, or ATP. This is the molecule that many body functions require to do work, such as facilitated diffusion, muscle movement, and yep, you guessed it-- thinking. The sodium ion pump that creates a gradient in the nerve cell interior allows for the inside of the cell to become positive. The combination of the ATP- using sodium ion gradient and the two diffusion- using potassion and sodium channels allows for the neuron to send an electric pulse down the axon. At the end of the cell, called the transmitter, the pulse allows ligands (or signal molecules) to continue the message to the next brain cell, which will send another signal until the message reaches its intended destination.

    ...Scientific evidence as to why proctors should let us return to our bags for food. Physics says we need it to think! Post below with your favorite brain food! Mine is a chocolate chip cliff bar, and I know a certain math geek's is a buffalo chicken wrap

    Happy post-APs, everyone!

    --Alpha Geek
  16. AlphaGeek
    You are a Kerbal physicist for Kow Jumped Over the Mun, a company that excels in anything spacey or astronaut-y. Your co-worker, Kirby McKerbin, is arguing with the desk clerk Moony Muni. Because you clearly have nothing better to do until next launch, you decide to listen in. Kirby is absolutely convinced that if he were to oscillate a pendulum on Kerbin, move it to Mun, and repeat the same occilation, the period of the pendulum on Mun would be roughly 3.5 times that of the period of the pendulum on Kerbin. The clerk argues that the period on mun would be 2.5 times that of the period on Kerbin. Settle this mess! Who's right and who should be working at McKerbals (Kerbin's largest fast food restaurant chain)?

    ****HINT: the surface gravity of Mun and Kerbin can be found on this site >> http://wiki.kerbalspaceprogram.com ******

    ...Scary but true. They can't tell the females from the males in our species, either.
  17. AlphaGeek
    For those of you who don't know, there is a video section of the Aplus site that features videos of physics-y origin. You can get there by clicking the word "videos" on the top blue bar of the site.


    When I first saw this video, it was floating among intense brain-teasing physics vids and real life examples of the science. I thought it deserved some defense for its place on the site, so let me explain what this despicable me mini clip has to do with physics.

    The most notable physics-feature of the video is that the geeky character's name is Vector, as he explains both verbally and through body language. A vector quantity is a magnitude with direction. For example, velocity is a vector quantity. A velocity of 3 m/s to the right has both units (meters per second) and direction (to the right). 3 m/s alone, a speed, is not a vector quantity because even though it has units, it does not have a direction. We call this a scalar quantity.

    I hope that explains Vectors joke, "I'm committing crimes with both direction and magnitude!" If he were the evil Dr. Scalar, it would only have magnitude. Haha! Ha. Ha... Ha.

    ...And I didn't notice this before, but when Vector first comes into the scene he crosses his arms while doing the "vulcan salute," which is actually the nerdfighter salute (You know! Vlogbrothers on youtube). I thought that was really cool. I wonder if it wasn't even supposed to be there in the first place, but some nerdy producer put it in

    Not familiar with vlogbrothers? Do acquaint yourself via nerd humor:

    ...Just for the record, my favorite part of the movie is as follows:

  18. AlphaGeek
    In an episode of Tom and Jerry from 1948, Tom once again has his face smashed in from a falling object. This time, the offender was a half-ounce canary wielding circular cage parts. The bird unfastened the cage bottom and let it drop onto the unsuspecting feline below, making Tom's face into a pancake. How much force does this pan actually make? Could it really damage a cat's face?


    First, we must find the velocity of the pan when it hits Tom's face. We know that the pan falls from rest, its acceleration is 9.81 m/s2, and the time it takes to fall from the cage to Tom is roughly 3 seconds (1:09 -1:12 in the youtube video). Using the equation Vf = Vi + at, we find that the velocity of the pan just before it comes into contact with Tom's face is 29.43 m/s.

    Let's estimate that the pan weighs roughly .1 kg (100 g). Also, let's estimate that the time it takes the plate to go from its initial velocity just before coming into contact with Tom's face and the time when it's final velocity reaches 0 m/s is roughly 1 tenth of a second (.1 s). We know that momentum is conserved in this situation and that (Force)(change in Time) = (mass)(change in velocity). Using this, we know that the change in velocity is -29.43 m/s, so the force of the pan on Tom is roughly 30 newtons. This is equal to roughly 6.7 lb of force.

    It takes anywhere from 7 to 9 lb of force to break a human nose, so even though it's not likely that the bird cage would've smashed the kitty's face in, he might very well lose his sense of smell.

    Here's a blast from the past composed of 40 % physics and 60% pain. Disclaimer: I do not promote domestic animal abuse, nor do I reccomend testing 7 lbs of force on your friend's nose.

  19. AlphaGeek
    So. I was reading my Biology textbook the other day and encountered something called "water potential." A simple summary of this term is water's potential energy , or it's capacity to perform work when free water moves from high water potential to low water potential. What? Physics in biology you say? Of course! :eagerness: Physics is everywhere.

    Let's define water potential in depth. Water potential is given by the equation water potential (symbol = Greek letter psi) = potential due to solute concentration + potential due to pressure, or:
    The potential due to solute concentration, or solute potential, is directly proportional to the number of dissolved solute molecules. Solute binds water therefore reducing the number of free water molecules and decreasing it's capacity to do work. Because of this, solute potential is negative.

    potential due to pressure, or pressure potential, is the physical pressure on a solution. Tension due to pressure is a negative pressure potential, whereas an applied pressure creates a positive water potential.

    The biology part of water potential is that it is essential to a cell's well being (plant cells in particular). The water potential determines the direction of movement of water in/out of a cell. For plant cells, it determines the shape and stiffness of the cell. A plant cell is flaccid initially. It becomes turgid when it intakes free water in that the pressure from the water pushes on the cell wall, making the cell swell. The cell becomes plasmolyzed when free water leaves the cell, causing the cell to shrivel and the cell membrane to pull away from the cell wall. This state is dangerous for a plant (commonly known as wilting) and the plant may die. These conditions are created by unequal water potentials of the cell vs the cell's surrounding environment. If a cell has a lower water potential than the surrounding solution, it will intake free water and become turgid. If the cell has a higher water potential than it's surrounding environment, it will expel free water and become plasmolyzed.


    If you'd like to know more about water potential, didn't understand a thing I just said or would like background noise doing homework, the following link may be of use to you:

  20. AlphaGeek
    So far, no other particle has been able to move at the speed of light. However, human beings are capable of seeing light move. Ramesh Raskar and his team at MIT have developed a camera capable of capturing light at 1 trillion frames per second. This method, called fempto photography, can take slow motion videos of light in motion. Watch the video for a better explanation but for those of you in a rush below is a summary of MIT's amazing research.

    As shown in the video, Raskar uses a laser to send a packet of photons through an object. Using fempto photography, the MIT team created videos of light traveling through a coca cola bottle and washing over a tomato.

    The group presents promising applications of their technology, such as finding survivors in unsafe conditions or hiding beings as well as exploring inner organs by seeing around corners with light.

    Perhaps the most interesting aspect of this video is featured in 9:20 - 10:04, in which time appears to be moving in reverse according to the camera's images. How is this possible? Watch to find out! Weird things happen when humans try to go faster than the speed of light

    Watch Ramesh Raskar's presentation below:

    http://www.ted.com/talks/ramesh_raskar_a_camera_that_takes_one_trillion_fra mes_per_second.html
  21. AlphaGeek
    ...can all be found at a fencing tournament! It's about time that fencing found it's way onto this forum. Fencing is an Olympic sport consisting of three weapons, epee, sabre and foil. In foil and epee, the opponent must hit their opponent's target area with their tip in order to score a touch. In sabre, the fencer may hit with the tip and/or the side of the blade to score a touch.

    I stumbled upon these fencing related physics applications by Ann McBain Ezzell, an MIT alumini. GIve the questions a shot, but if nothing else, read through them as they are quite humorous.

    A few comments on the question's content:
    1. Fencers scream/yell during bouts. Odd, but true. A fencer may do this to celebrate a touch, frighten their opponent or convince the referee that they scored a touch. (Some sound like howls [Div 1 men's foil], others like pterodactyls [youth 12 women's epee]. My favorite yell is "YAZEE!," used frequently by a fencer at the University of Rochester).
    2. Fencers sometimes thow their equipment when they are angry. If they do, the referee will likely black card the fencer and they are removed from the tournament (I've seen it happen, it's both frightening and comical).
    3. Most of the terms used below are actual names of fencers, equiptment, etc. For example, Peter Westbrook is the founder of the Peter Westbrook Foundation in New York City, an organization allowing people to fence who normally would not be able to afford it.

    Here is Ann's mock exam. I hope you have as much fun with this as I did!

    27 April 1989 - updated 11 December 1994

    [Disclaimer: All similarities between real fencers and characters in this exam are purely intentional and completely without malice.]

    Instructions: Answer all questions. Be sure to show your work (including, where appropriate, free body diagrams). Don't screw up the math. Except as noted, you may neglect air resistance and friction.

    1. A 2m tall Italian epee fencer loses his last repechage bout by being pushed off the end of the strip (standard 14m length). He knocks his mask straight into the air and simultaneously kicks his reel, which had been positioned at the end line, towards the other end of the strip. The mask just touches the 6m high gym ceiling before starting its downward descent. The fencer sees the reel barely clear the head of the 1.75m tall referee, who is standing in front of the scoring table recording the result. Just as he is knocked unconscious by his plummeting mask, he sees the reel land at the feet of the chairman of the Directoire Technique, who had been watching the bout from the far end of the strip.
    a) How long does it take the reel to reach the ground?
    Calculate the initial magnitude and direction of the reel.
    c) How long will it take after the fencer regains consciousness until he is expelled from the competition?

    2. Claus Block is bouncing up and down two meters from his opponent's end of the strip. His reel has slipped to 1.5 meters in front of his end line, and the reel cord is attached to his waist 1m above the ground. The mass of the exposed portion of the reel cord is 500g. A standing wave of three loops is being produced in the reel cord.
    a) If Claus hits the ground 10 times per second (it's the finals), what is the tension in the reel cord?
    Assume that the tension in the reel remains as calculated in part (a). Where would Claus have to stand and bounce, relative to his initial position, to produce a standing wave with only two loops?

    3. A brand-new Uhlmann epee point is constructed such that the total travel is exactly 1.5mm, and it just passes the 0.5mm shim test. When a test weight of 750g is gently dropped onto the tip, the scoring machine light comes on. After the machine resets, the light remains off. However, any further depression of the tip causes the light to come on.
    a) Calculate the spring constant (k) for the point spring (you may neglect the mass of the tip).
    A Russian point is dimensionally identical to the Uhlmann point, but friction in the point produces an extra 1N of resistive force. Since its owner cannot readily fix his weapons, the point spring must be strong enough to lift 2kg (as above), to ensure that his weapons will never fail on the strip.
    Calculate the spring constant (k') required for this point spring.
    The two weapons are fixed horizontally, tip to tip, then the retaining screws are removed to allow free movement of the tips. The two tips are displaced 0.5mm from their equilibrium position and then released.
    c) Calculate the frequency of the resultant SHM. (Assume that the mass of 1 tip is 1g and that both tips move together.)

    4. Yuri Rabinovich and his long-lost identical twin brother Pavel (each with mass 65 kg) are fencing sabre. With weapon arms half-extended, they launch simultaneous fleche attacks and lock bell guards in mid air. Just before impact, each is traveling at a speed of 5m/s. When their bodies pass, the centers of mass are 1m apart. The bell guards remain locked and their arms extend to full length (adding 1m to the distance between the centers of mass).
    a) What is the angular momentum of the resultant tangle immediately following the collision?
    When the arms are extended, what is their rotational frequency in revolutions per second?

    5. In the midst of a team free-for-all, Frank MacKenzie (mass 90 kg) picks up Lara Tomasso (mass 65 kg) and attempts to hold her at arm's length (this would put her center of mass 1m from his center of mass). Frank has enough upper body strength to support a mass of 25kg in this manner.
    a) Frank, being an engineer, starts to spin. After accelerating for 5 seconds at a constant rate, his arms are forming an angle of 5 degrees with the horizontal. Find his angular acceleration.
    At this same acceleration, how long will it take until his arms are 2.5 degrees from the horizontal?
    c) How long before his arms are perfectly horizontal?
    d) How long will it be before Lara throws up?

    6. a) The maximum length of a foil blade from tip to bell guard is 90cm. Taking the pivot point to be at the bell guard, calculate the torque produced by a force of 20N applied perpendicular to the blade at the following distances from the tip of the foil:
    1) 85 cm
    2) 50 cm
    3) 10 cm
    If you are able to produce a torque of 10Nm around your own bell guard, calculate the resultant torque around your opponent's bell guard if your blades are pushing at right angles to each other and the intersection point is 10 cm from your bell guard and 45 cm from your opponent's bell guard.

    7. Assume that a foil blade (not including the tang) is a uniform rod of length 90cm, diameter 5mm and mass 150g. Your opponent beats your blade sharply 40cm from the tip, breaking the blade. She then immediately does a circle disengage and hits the free end of the broken piece with a 20N force for .01 second. Calculate the rotational frequency of the broken piece of blade as it spins off end over end. (The rotational inertia, I, for a uniform rod of length L is 1/12mL^2, with the axis of rotation at the center of the length of the rod.)

    8. A golf ball of mass 46g hangs from an ideal string 1m in length. A diligent epee fencer practicing point control strikes the ball with sufficient force to cause the string to form an angle of 15 degrees with the vertical.
    a) What is the velocity of the golf ball immediately following impact?
    How long after impact will it take the ball to reach the point where it is closest to the fencer?

    9. Peter Westbrook (mass 70kg), having temporarily forgotten the end-of-strip rules in the heat of the finals, retreats rapidly off the end of a raised piste 0.30m high. Fortunately for Peter, the regulation run-off incline of 2m has been included.
    Unfortunately, he trips and ends up rolling ignominiously the entire length of the incline. Assume that Peter's body approximates a cylinder of 50cm diameter as he rolls without slipping down the incline. Further assume that he is not moving horizontally when he hits the top of the ramp.
    a) If Peter is making 2 revolutions per second when he reaches the bottom of the incline, what was his angular momentum when he hit the top of the incline?
    What torque is required to stop Peter's rolling at the bottom of the ramp in 1 second?

    10. Isabelle Hamori shrieks in the heat of combat at 13,000 Hz. The gym is set up with pairs of two meter wide strips three meters apart, with six meters between each pair.
    a) If Isabelle is fencing in the middle of strip 11 at the far end of the gym from the Bout Committee table, which is 10 meters from strip 1, how much longer will it take the Chairman of the Bout Committee to wince than Isabelle's referee, who is standing halfway between strips 10 and 11? (This is at the 1988 Chicago Nationals, where the ambient temperature is approximately 40 degrees C. Take the speed of sound in air at 20 degrees C to be 340 m/s and remember that the speed of sound is related to the square root of the temperature in degrees Kelvin.)
    Isabelle's opponent is MJ O'Neill, also known for her dulcet tones on the strip. MJ screeches while fleching at Isabelle, who attempts to retreat, at full voice. The referee, who is maintaining his original position relative to Isabelle, notices that the combined shrieking is producing 2 beats per second. If MJ screeches at 12,980 Hz, what is her minimum velocity relative to Isabelle?

    Leave it to an MIT student to make a kick-butt exam. All credit goes to Ms Ezzell!

    --AlphaGeek :fight)
  22. AlphaGeek
    Just thought we could benefit from some review on moment of inertia, because it was a pretty extensive topic and wasn't really mentioned in physics B. Not to mention that the variable is a different expression for each object.

    The general form of the equation is I = ∑i miri² = ∫r² dm .

    Below are the moment of inertia equations for a few different objects. If you have another object in mind to share, please do add it in the comments!

    Isolid disc = 1/2 mr2
    Icylinder about its axis = 1/2 mr2
    Ihollow disk/hoop = mr2
    Isolid sphere= 2/5 mr2
    Ihollow sphere= 2/3 mr2
    Irod about it's center= 1/12 ml2
    Irod about it's end= 1/3 ml2

    Though these shortcuts are great, make sure to know how do derive the moment of inertia of an object. For review, here's how to calculate the moment of inertia of a rod from it's end (Also in the textbook p 273 as well as in the notes packets).

    The linear mass density (λ) = M/L, where M is the mass of the uniform rod with length L.

    dm = M/L dx, or the mass density times the little wee bit of rod.

    Using the general equation, we know I = ∫oLx2 dm, where x is the length of the rod from x=0 to x=L.
    By substituting for dm, we then know I = ∫oLx2 (M/L) dx.
    The constant comes out, leaving I = (M/L) ∫oLx2 dx.
    And using calculus, we get I = (M/L) (1/3)x3 evaluated from L to 0, which leaves us with
    I = (1/3) (M/L) (L3)
    I= (1/3) ML​2

    Note: If you need further assistance on this topic, the unit packet for Rotation (with the frog on a unicycle in it) and the packet titled "Chapter 6: Rotation" are useful. However, for visuals and more elaborate derivations, I recommend reading Tipler p. 272 and the pages following and/or watching this video again:


    ...Which I always find extremely helpful. I'll probably post another unit summary again, since our midterm is looming in the near future. Best of luck, all!
  23. AlphaGeek
    Having trouble on the 4 minute drill? Need to consolidate your thoughts for the Mechanics part of the AP-C exam? Have no fear! I've sifted through my notes to find a good portion of the mechanics equations. If you find anything missing/incorrect, PLEASE give feedback in the comments section! I'll edit the changes in ASAP. Thank you


    Vectors etc.

    A B = lAl lBl cos Ө
    A x B = - (B x A)
    lA x Bl = lAl lBl sin Ө


    V= Vo+ at
    Δx = Vo t + (1/2) a t2
    V2 = Vo2 +2aΔx

    Δx = ∫ v(t) dt
    Δv= ∫ a(t) dt
    Vavg = Δx/Δt = (Xf - Xo)/(tf - to)
    V= dx/dt
    a= dv/dt


    Fc = mv2/ r
    ac = v2/r = w2/r

    Fg= GMm/r2
    Ug= -GMm/r

    Rotational Motion

    S= Өr
    v= wr
    a= αr

    w= ΔӨ/Δt
    ac= w2r
    Vlinear = 2πr/t

    parallel axis theorem: I = Io +md2

    KEroll= (1/2)Icmw2 + (1/2)mv2

    Angular momentum (L) = r x p = mvrsinӨ = mwr2sinӨ
    dL/dt = Torque
    L= w I
    K= (1/2) I w2

    Moment of Inertia

    I = Σmi(ri)2 = ∫r2dm
    Isolid disk = (1/2) mR2 (also works for a cylinder about its axis)
    Ihoop = mR2
    Isolid sphere = (2/5)mR2
    Ihollow sphere = (2/3)mR2
    Irod about center = (1/12)mR2
    Irod about end = (1/3)ml2

    Torque (T)

    x >> Ө
    v >> w
    a >> α
    m >> I
    F >> T

    ΣF = ma >> ΣT = Iα
    T = rxF = rFsinӨ
    T = (Radius)(tension)

    Center of Mass

    rcm = Σmr/Σm = ∫r dm / Σm
    Xcm = (m1x1 + m2x2)/ (m1+m2)

    Drag force

    Fd = bv = cv2
    VT = mg/b
    V = VT(1 - e(-b/m)t)= (mg/b)(1 - e(-b/m)t)

    Ff= μ Fn

    ...As to not get long and confusing, I'll make another blog post with all of the Electricity & Magnetism equations that I have in it. Check that post out, too!

    --Alpha Geek
  24. AlphaGeek
    HAPPY NEW (school) YEAR EVERYBODY!!! I'm super excited for some serious Physics C. Just set up my account! I found this comic online and thought it would be a great way to break the ice:

    Hee hee. And of course I'll site my oh-so-credible source: http://memebase.cheezburger.com
    ...Although they did spell cheeseburger wrong. ^-^; And look, I found a fencing smiley face!:fight)

    --Geek out!
  25. AlphaGeek
    Many of you are familiar with the children’s movie happy feet, about a whimsical penguin chick that just can’t stop dancing. Why don’t these birds fly instead of dance, you ask? Let’s use physics to figure out why Mumble is aerially challenged:
    There are four main forces involved in avian air travel: lift, weight, drag, and thrust.
    As shown by the diagram of a blue jay in flight (credit to http://www.lcse.umn.edu), lift opposes weight and thrust opposes drag. A bird is able to fly when lift is greater that weight and thrust is greater than drag. Read below for more on these forces:
    1. Weight: Mass x acceleration due to gravity
    2. Lift: This force can be explained using Bernoulli’s principle—as a fluid’s velocity increases, the pressure decreases and vise versa. Bird wings are in an airfoil shape with a bump on the top and a smooth bottom (like an air plane wing). The air is forced to move faster over the top of the wing than on the bottom because it has a longer distance to travel over the bump. Like faster moving fluids, faster moving air causes the pressure on top of the wing to be lower than on the bottom of the wing, allowing the bird to lift upward.
    3. Drag: This force is caused by air resistance. The more aerodynamic the flier, the less drag that will act upon the flier.
    4. Thrust: This is the force created to push the bird forward. Birds create thrust by the backward push of their wing, like humans do when we push backward with our arms to swim in a pool. Plane propellers and jet engines create thrust for a plane.

    In short, the reason why Mumble cannot fly is because penguins store fat to keep themselves warm, increasing their weight. Their wings also are not the correct shape or size to produce enough lift to get into the air. Weight > Lift, therefore Mumble dances.

    Next time, lay off the fish.

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