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Everything posted by AlphaGeek

  1. Oh jeez, Charlie 3, class 0. Nice job! Two cookies tomorrow then, remind me in Physics :glee:
  2. You're not alone, the abstractness of E&M kind of worries me, too. But we'll work though it! :tiger: After all, there's a whole half a year of fun ahead
  3. AlphaGeek

    Moon Boots!

    Not going to lie, I'm extremely jealous of your moon boots! Comfy and colorful, where can you go wrong? :wave)
  4. Good point, goalkeeper! Overpasses and snow drifts are especially dangerous this time of year. :snowman: Thanks for the warning with evidence
  5. 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. SO, because everyone else decided to take a break, my brain also decided to go off on holiday for a while. In that case, I've decided to make this blog post 100% fun (yet still on topic), and what's more fun and physics related than comics? Hope these tickle your funny bone, have a great break everyone!!! ...And finally, a comic that Mr. Fullerton would enjoy: Have a great break! Make sure to relax (and pretend that midterms aren't coming up)! --Alphageek
  7. Credit to Mr. Powlin (who read this last year about the same time) and Snopes.com, where I found this humorous commentary once again. For those of you who did not hear this last Christmas or those who want to get into the spirit of the physics-filled holiday season, I thought I'd post this up for a few giggles. Happy Holidays, all! :snowman: No known species of reindeer can fly. BUT there are 300,000species of living organisms yet to be classified, and while most of these areinsects and germs, this does not COMPLETELY rule out flying reindeer which onlySanta has ever seen. There are two billion children (persons under 18) in the world.BUT since Santa doesn't appear to handle the Muslim, Hindu, Jewish and Buddhistchildren, that reduces the workload to 15% of the total — 378 million according to Population ReferenceBureau. At an average (census) rate of 3.5children per household,that's 91.8 million homes. One presumes there's at leastone good child in each. Santa has 31 hours of Christmas to work with, thanks to thedifferent time zones and the rotation of the earth, assuming he travels east towest (which seems logical). This works out to 822.6visits per second. This is to say that for each Christian household with goodchildren, Santa has 1/1000th of a second to park, hop out of the sleigh, jumpdown the chimney, fill the stockings, distribute the remaining presents underthe tree, eat whatever snacks have been left, get back up the chimney, get backinto the sleigh and move on to the next house. Assuming that each of these 91.8 million stops are evenly distributed aroundthe earth (which, of course, we know to be false but for the purposes of ourcalculations we will accept), we are now talking about .78 miles per household, a total trip of 75½ million miles, not counting stops to do whatmost of us must do at least once every 31hours, plus feeding andetc. This means that Santa's sleigh is moving at 650 miles per second,3,000 times the speed of sound. For purposes of comparison, the fastestman-made vehicle on earth, the Ulysses space probe, moves at a poky27.4miles per second — a conventional reindeer can run, tops, 15 miles per hour. If every one of the 91.8 million homes with good children were toput out a single chocolate chip cookie and an 8ounce glass of 2% milk, the total calories (needless to sayother vitamins and minerals) would be approximately 225 calories (100 for the cookie, give or take, and125 for the milk, give or take). Multiplying the number of calories per houseby the number of homes (225 x 91.8 x 1000000), we get the total number ofcalories Santa consumes that night, which is 20,655,000,000 calories. To breakit down further, 1 pound is equal to 3500 calories. Dividing our total number of caloriesby the number of calories in a pound (20655000000/3500) and we get the numberof pounds Santa gains, 5901428.6, which is 2950.7tons. The payload on the sleigh adds another interesting element.Assuming that each child gets nothing more than a medium-sized lego set (twopounds), the sleigh is carrying 321,300 tons, not counting Santa, who isinvariably described as overweight. On land, conventional reindeer can pull nomore than 300 pounds.Even granting that "flying reindeer" (see above) could pull TEN TIMESthe normal amount, we cannot do the job with eight, or even nine. We need214,200 reindeer. This increases the payload (not even counting the weight ofthe sleigh) to 353,430 tons. Again, for comparison, this is four times theweight of the Queen Elizabeth.353,000 tons traveling at 650miles per second createsenormous air resistance — this willheat the reindeer up in the same fashion as spacecraft re-entering the earth's atmosphere. The lead pairof reindeer will absorb 14.3QUINTILLION joules ofenergy. Per second. Each. In short, they will burst into flame almost instantaneously,exposing the reindeer behind them, and create deafening sonic booms in theirwake. The entire reindeer team will be vaporized within 4.26 thousandths of a second. Santa, meanwhile, will besubjected to centrifugal forces 17,500.06 times greater than gravity. A250-pound Santa (which seems ludicrously slim) would be pinned to the back ofhis sleigh by 4,315,015 pounds of force. In conclusion: If Santa ever DID deliver presents on ChristmasEve, he's dead now.
  8. Oh jeez, that stinks! Hope that your door gets fixed soon
  9. That's interesting. I feel like majors are getting more and more specific. For example, renewable energy engineering blends together elec., mechanical, and other forms of engineering with a focus on solar, wind, and like power sources. Specific majors are neat because they're specialized to a particular focus area, directly preparing the student for a future career set. Great find, Goalkeeper!
  10. *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
  11. Thank you! As you can see, my artistic talents are no joke
  12. Yay! Congrats Charlie, I'll bring you in a cookie tomorrow
  13. 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? [ATTACH=CONFIG]553[/ATTACH]
  14. Thank you Mr. Fullerton! The videos do help a ton
  15. Lol, a very hot topic I suppose 1. http://www.aplusphysics.com/forums/entry.php?702-Fempto-Photography-Captures-Light-in-Motion 2. http://www.aplusphysics.com/forums/entry.php?703-Watching-light-move 3. http://www.aplusphysics.com/forums/entry.php?776-Slow-Motion-of-Laser-Pulse-Traveling-Through-a-Coke-Bottle#comments
  16. 0.o Impossible! Text can't do handstands...
  17. ...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. [ATTACH=CONFIG]542[/ATTACH] 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! FENCING PHYSICS FINAL 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)
  18. AlphaGeek

    Physics Jokes

    Hahaha, just laughed out loud at that one. Forever alone.
  19. AlphaGeek


    Haha, awesome You should juggle for us sometime! He really should have shoes on... Juggling fire and all, no big deal really.
  20. I've never seen one, but that is a very cool concept. Thanks for sharing! ...And that's a shame about your coffee mug, Dave. I'm sure it was treasured.
  21. Oh, I heard about that when visiting Case Western a little bit ago! A group of students thought that one up. The link below gives more info. Not bad for Undergrads http://www.changinggears.info/2012/04/16/undergrads-at-case-western-build-a-better-pothole-patch-score-one-for-midwest-innovation/ http://youtu.be/XrvzZewPUJA
  22. Lol, yeah that's pretty much it. Math applies to everything... ...even in the selection of a significant other. Details are very important, especially in calculus-based physics. And love. (<3 xkcd)
  23. How would I determine the drag coefficient of an organic shape, such as a blob of pudding or a chicken or a Looney Tunes character? I wanted to do a blog post on the terminal velocity of Wile E. Coyote falling off of a cliff. I went back into my notes and found the following equations: Air resistance = Fdrag = bv = cv2 VT= (mg)/b V = VT ( 1 - e(-b/m) ) Notice the constants, b and c. I turned to google, thinking that the constants would be relatively easy to find. It turns out, the equation for Vterminal is a little more complex than I thought. [ATTACH=CONFIG]532[/ATTACH] Finding V terminal involves the mass of the object, acceleration due to gravity, the density of the medium that the object is traveling through, the area effected, and, of course, a drag coefficient. In my quest to find the drag coefficient, I found that the coefficient is related to the shape of the affected surface area. The lower the drag coefficient, the more easily the object can move through the air. The following table helps illustrate this: [ATTACH=CONFIG]533[/ATTACH] That's fine and well if you're trying to find the terminal velocity of a UPS box falling from a cargo plane in air of know density, although there are a few complications in the Wile E. Coyote situation. My number one probelm is as follows: unless the furry critter assumes a fetal position and magically transforms his body into a perfect sphere, his coefficient is difficult to determine. Any suggestions? :dontknow)
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