What is Fall: Definition and 922 Discussions

Autumn, also known as fall in North American English, is one of the four temperate seasons. Outside the tropics, autumn marks the transition from summer to winter, in September (Northern Hemisphere) or March (Southern Hemisphere), when the duration of daylight becomes noticeably shorter and the temperature cools considerably. Day length decreases and night length increases as the season progresses until the Winter Solstice in December (Northern Hemisphere) and June (Southern Hemisphere). One of its main features in temperate climates is the shedding of leaves from deciduous trees.
Some cultures regard the autumnal equinox as "mid-autumn", while others with a longer temperature lag treat the equinox as the start of autumn. In the English-speaking world, autumn traditionally began with Lammas Day and ended around Hallowe'en, the approximate mid-points between midsummer, the autumnal equinox, and midwinter. Meteorologists (and Australia and most of the temperate countries in the southern hemisphere) use a definition based on Gregorian calendar months, with autumn being September, October, and November in the northern hemisphere, and March, April, and May in the southern hemisphere.
In North America, autumn traditionally starts with the September equinox (21 to 24 September) and ends with the winter solstice (21 or 22 December). Popular culture in the United States associates Labor Day, the first Monday in September, as the end of summer and the start of autumn; certain summer traditions, such as wearing white, are discouraged after that date. As daytime and nighttime temperatures decrease, trees change colour and then shed their leaves. In traditional East Asian solar term, autumn starts on or around 8 August and ends on or about 7 November. In Ireland, the autumn months according to the national meteorological service, Met Éireann, are September, October and November. However, according to the Irish Calendar, which is based on ancient Gaelic traditions, autumn lasts throughout the months of August, September and October, or possibly a few days later, depending on tradition. In the Irish language, September is known as Meán Fómhair ("middle of autumn") and October as Deireadh Fómhair ("end of autumn"). Persians celebrate the beginning of the autumn as Mehregan to honor Mithra (Mehr).

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  1. P

    Clouds are water liquid, not vapour, why it don't fall down?

    Title says all, why clouds are up? have the air more density than water? Thanks!
  2. D

    Fall with Air Drag - Which Value for Velocity to Use?

    Homework Statement I want to numerically simulate a fall with air drag. In class, we used these equations to produce a table simulating free fall (using a ti calculator): dt=0.1s a=9.81m/s² tn+1=tn+dt vn+1=vn+a*dt xn+1=xn+vn*dt When I compared that system with the curve produced by the...
  3. M

    How fast did the rock strike the ground?

    Homework Statement A rock thrown straight up climbs for 2.50 s, then falls to the ground. Neglecting air resistance, with what velocity did the rock strike the ground? Homework Equations well we are looking for v=? we have: t=2.50 s and g=9.8 ^do we need gravity? yes, right? =S...
  4. L

    Electrons and positrons free fall within a superconducting cylinder

    I read about electrons and positrons free fall within a superconducting cylinder, in this book (p 105): https://www.amazon.com/dp/0521675537/?tag=pfamazon01-20 I don't understand what I read. Apparently, electrons would feel an electric field mg/e that would actually freeze them in the...
  5. J

    Calculating Rod's Speed After Free Fall

    Homework Statement From the GRE 0177 practice exam: A thin uniform rod of mass M and length L is positioned vertically above an anchored frictionless pivot point, as shown above, and then allowed to fall to the ground. With what speed does the free end of the rod strike the ground? The...
  6. U

    Do Balls Thrown Up and Dropped Down Meet Above the Halfway Point of a Building?

    Homework Statement A ball is dropped from rest from the top of a building and strikes the ground with a speed vf. From ground level, a second ball is thrown straight upward at the same instant that the first ball is dropped. The initial speed of the second ball is v0 = vf, the same speed...
  7. J

    Particle Falling g=1m/s^2 how much time does it take to fall?

    Homework Statement A particle falls freely through a distance of 1.00 m starting from rest. Assume resume that g = 10 m/s^2. How much time does it take to fall? (4E-1) Homework Equations I think a=vf-vi/t The Attempt at a Solution I've tried 10m/s^2=1/10m/s-0/t And tried to...
  8. X

    How Much Force Does a Falling Boy Exert on a Net?

    Hello Homework Statement I have this problem, even though it might seem very simple. A boy falls from a distance and lands on a net. When he reaches the net, it de-accelerates him with 4*g. The question is: What amount force does the boy exert the net? The Attempt at a Solution I would say...
  9. H

    Need help with the sign of g in free fall acceleration

    Homework Statement Heather and Jerry are standing on a bridge 50\;m above a river. Heather throws a rock straight down with a speed of 20\;m/s. Jerry, at exactly the same instant of time, throws a rock straight up with the same speed. Ignore air resistance. How much time elapses between the...
  10. J

    Do Objects with Different Masses Fall at the Same Rate in Air?

    I've tried finding this in the forums elsewhere, but can't seem to find the answer I'm looking for. So here's my dilemma... There are two objects, object X and object Z, that are the same volume and shape. However, object X has a greater mass than object Z. Objects X and Z are both dropped...
  11. A

    Free Fall: Does an Object Reach Speed of Light?

    In free fall, there is no air resistance, so the only force acting upon the object of free fall would only be its weight. Now the question is, if an object keeps accelerating due to free fall, wouldn't it eventually reach the speed of light? For example, Earth's g=9.81 m/s^2, so over a course...
  12. J

    Free fall: total distance expressed in terms of distance fallen in nth second

    Homework Statement A body falls vertically from rest. During the nth second it falls a distance d. Prove that by the end of the nth second it has fallen a total distance (D) of (2d+g)^2/8g Homework Equations x = x0 + V0 + 1/2at^2 where x0 = initial position v0 = initial velocity a...
  13. JasonJo

    Admissions Fall 2009 Graduate Admissions Thread

    This is a thread for all us nervous Fall 2009 grad applicants. All my applications are in and all my letters of recommendation were sent in. I don't want to post any stats or profile data until I get my admissions decisions in. Where did you guys apply? What field do you want to pursue...
  14. L

    How High and How Long Will the Apple Travel?

    Homework Statement maria throws an apple vertically upward from a height of 1.3 meters with an initial velocity of 2.4 m/s. A) will the apple reach a friend in a treehouse 5.3 m above ground B)how long will the apple be in the air before it hits the the ground Homework Equations...
  15. A

    What is the height of the cliff?

    1. To determine how high a cliff is, a llama farmer drops a rock, and then 0.800 s later, throws another rock straight down at a velocity of −10.0 m/s. Both rocks land at the same time. How high is the cliff? 2. I know some kinematics equations must be used 3. I am stumped...
  16. D

    How to Create Linear Rise and Fall Edges in a Circuit

    I need help with a circuit. I need to run the signal in first image through a circuit that can clean up the exponential rise and fall edges and make it more linear. Can anyone help. http://picasaweb.google.com/davidanthonypitts/SignalWaveforms?authkey=5iLxB--Xdqs#
  17. C

    Please check my Answer to Free Fall Question

    Homework Statement A man standing on the sidewalk throws a set of keys vertically upward to his wife in the window of their apartment 4.0 m above. The wife catches the keys 1.5 s later. (a) With what initial speed were the keys thrown? (b) What is the velocity of the keys just before they were...
  18. Wellesley

    News Oil Prices in 2009: Will They Rise or Fall?

    Will oil prices rise in 2009? Or will the economy keep the prices down for a while?
  19. R

    Solving for the Distance of Fall for 4kg Block

    Homework Statement A block of mass 3 kg is hung from a spring, causing it to stretch 6 cm at equilibrium, as shown below. The 3 kg block is then replaced by a 4 kg block, and the new block is released from the position shown below, at which point the spring is unstretched. How far will the 4...
  20. M

    Issues with graduating in the fall

    I'm a second year physics major and I'm considering starting a co-op job doing research starting this summer. The outcome of this is that I would end up graduating in the fall, and my plan after school is to get a PhD. Since hardly any PhD programs start in the spring, I'd have a good 9 months...
  21. Andre

    The autumn (fall) picture thread

    So for the Autumn picture contest I chosed an awesome view of the Danube valley. Unfortunately the sun wasn't that bright that day. So the choice was scenery versus light. Scenery won, these were the losers:
  22. M

    Free Fall Trajectory? Simple answer

    Free Fall Trajectory So I am basically lost in what that means. I think it is the component method for vectors? Am I right? Some background on the lab: We rolled a marble down a curved ramp so that it went off the table and hit the ground in front of the table. (we marked where it hit with...
  23. A

    How Does Falling Water Affect Scale Readings?

    Homework Statement Water falls at the rate of 250 g/s from a height of 60 m into a 780 g bucket on a scale (without splashing). If the bucket is originally empty, what does the scale read after 2 s? Homework Equations p=mv F\Deltat=\Deltap The Attempt at a Solution So I assumed that the...
  24. L

    Yo-Yo Motion Puzzle - Find the Speed & Time of Fall

    Homework Statement The string in a yo-yo is wound around an axle of radius 0.512 cm. The yo-yo has both rotational and translational motion, like a rolling object, and has mass 0.206 kg and outer radius 1.88 cm. Starting from rest, it rotates and falls a distance of 1.20 m (the length of the...
  25. H

    Calculating the time it takes for something to fall over long distances

    Homework Statement This isn't really a homework question that I have but more of a question i am trying to find out myself. When objects are near the surface of the earth, objects accelerate at an average of 9.8 meters per second^2. However when we get farther away from the earth, say have...
  26. M

    Free fall ball velocity question

    Homework Statement a ball is thrown straight down from the top of a 220 feet building with an initital velocity of -22ft/s. What is the velocity of the ball after 3 seconds? What is the velocity of the ball after falling 108 feet? Homework Equations s(t) = -16t^2 + Vi(t) + si...
  27. T

    Free Fall and gravitational acceleration

    Homework Statement A ball is dropped from 1.5 y(m) and hits the ground in .54 t(s). What is the value of g (m/s^2)? The accepted value of g = 9.8m/s^2 Homework Equations y=1/2gt^2 The Attempt at a Solution I'm getting this wrong, but this is my attempt. 1.5 = 1/2g x .54^2...
  28. P

    Calculating Projectile Motion: Solving for Distance and Height

    Homework Statement A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 8.20 m/s at an angle of 15.0° below the horizontal. It strikes the ground 3.00 s later. (a) How far horizontally from the base of the building does the ball strike the...
  29. A

    Calculating Initial Velocity of a Projectile Using Free Fall Equations

    Homework Statement A stone is thrown upward at an angle of 51° above the horizontal. Its maximum height during the trajectory is 26 m. What was the stone's initial speed? m/s Homework Equations a=v2/r v2=vo2+2ax C=2\pir The Attempt at a Solution I figured the acceleration is...
  30. C

    Help Physics (I think its free fall)

    A doctor, preparing to give a patient an injection, squirts a small amount of liquid straight upward from a syringe. If the liquid emerges with a speed of 1.5 m/s how long does it take for it to return to the level of the syringe? what is the maximum height of the liquid above the syringe...
  31. S

    Finding maximum acceleration of truck without having package fall off.

    Homework Statement Anthony is going to drive a flat-bed truck up a hill that makes an angle of 10 degrees wtih respect to the horizontal direction. A 36.0-kg package sits in the back of the truck. The coefficient of static friction between the package and the truck bed is 0.380. What is the...
  32. glondor

    Indian Temple and the colours of fall

    It was such a beautiful day here in southern Ontario Barb and I decided to take a lil drive. We took a few photos on our trip. The Credit river valley is 2 minutes from our place, so we shot the fall colours. There are some beautiful colours right outside our apt. Next we drove to the area of a...
  33. T

    Solving Free Fall Problem: Initial Speed & Height for Same Time Impact

    Hello friends, I am very new to this forum and I´d like to consult you if i have any questions. Currently I am studying basic physics for my ug. I´d really apreciate it if you could help me out. Homework Statement A ball is thrown straight up from the edge of the roof of a building. A...
  34. D

    Computer Analysis of Free fall

    Sometimes Technology makes me happy, and sometimes it makes me cry, and THIS is definitely one of those times that it makes me cry. So we used a free fall program to give us values of the distance, velocity, time and acceleration. Then we had to graph it on Excel, and then find the...
  35. J

    The constant of motion of a free fall body

    1.what are the the constants of motion of a free fall body(treat this as a one-dimension motion,so there are two [independent] constants of motion )? 2.are they initial velocity and initial displacement? 3.and i know the total energy(T+V) is one,but they are not independent with the...
  36. Redbelly98

    See the Changing Leaves - Check the Latest Fall Color Maps!

    It's that time of year again. Or as Bob Dylan would say, "the leaves, they are a-changin'." I just found this cool website with maps of where the leaves are at peak color for parts of the USA. They update twice a week; go to these links and click on "Current _____ report" to get the latest...
  37. K

    Free Fall: Questions & Solution

    Homework Statement 45. A freely falling object requires 1.50 s to travel the last 30.0 m before it hits the ground. From what height above the ground did it fall? Homework Equations x = xi + Vit + (1/2)at2 Vf2 = Vi2 + 2ad The Attempt at a Solution First found the initial...
  38. G

    What are the characteristics of an object in free fall at the top of its path?

    HELP! PLEASE concepts in free fall an object is thrown upwards, at the top of the path it has a) zero acceleration b) maximum momentum c) maximum kE d) is at equillibrium e)none of the above i know accelarion is 9.8m/s^2 i also know is not KE since at the top is potential im...
  39. J

    Solve Free Fall Question: Earth vs Moon Gravity

    The moon's gravity is about one sixth of the Earth's. (Basically, one sixth of 9.80m/s^2). If two objects were dropped at the same height on the Earth and on the Moon, the time it would take for the object to reach the surface of the moon compared to the Earth is... a) 6 b) 36 c) Square root...
  40. Phrak

    Can anything fall into a black hole?

    From what I understand, from a frame of reference outside a black hole, it takes an infinite amount of time for a test particle to cross the event horizon. But it takes finite time for any black hole to evaporate. It seems there is no horizon left to fall through.
  41. D

    How Often Do You Fall Ill Annually?

    Ok this sucks. This is the second time this year I'm down with a fever and flu. The first time it happened last semester it lasted for 2.5 weeks. I'm just wondering how often you guys fall ill on average annually.
  42. A

    Motion (speed, acceleration, free fall, etc )

    Hi everyone! I have 7 questions here, I completed them all, but I’m not sure if I got them correct. I would greatly appreciate it if someone could have a look at them and let me know if I need to fix anything - I had the most trouble with question 3. Thank you so much for your time! :smile...
  43. J

    How Long Does a Flea Stay in the Air After Jumping? Find Out Now!

    A flea jumps straight up to 0.390m. How long does it stay in the air from the time it jumps up to the time it lands? First of all, I found the initial velocity. with the initial velocity, i tried using the equation d = v1t + 1/2at^2 to get the time. but apparently it's wrong...;; How do...
  44. B

    Will a Rock Thrown Upward Reach the Top of a Castle Wall?

    Homework Statement an attacker at the base of a castle wall 3.65 m high throws a rock straight up with the speed 7.40 m/s at a height of 1.55 m above the ground. a.) will the rock reach the top of the wall? b.) if so, what is its speed at the top? if not, what initial speed must it have to...
  45. C

    Time taken to free fall to centre of earth - if allowed?

    Hi, Some time back I was saw a discovery documentary, can't remember the name, but in that somewhere they told that under free fall if possible to centre of earth, it will take around 32 Hrs or so.. No calculations or details were given. So I wonder will it take so much time or how...
  46. K

    Calculate Height of Freely Falling Object - 30m in 1.5s

    A freely falling object requires 1.50 s to travel the last 30.0 m before it hits the ground. From what height above the ground did it fall? I have been working on this for a while and seem to be going wrong somewhere. I am unclear as to how free fall is meant here. I know that it need...
  47. B

    Free fall of a stone off a cliff

    I am having trouble with this one. for all the formulas I tried I need the velocity, which they don't tell us in the problem. Any help would be appreciated . A stone falls from rest from the top of a cliff. A second stone is thrown downward from the same height 2.4 s later with an initial...
  48. X

    Help with kinematics in one dimension free fall

    Homework Statement A wrecking ball is hanging at rest from a crane when suddenly the cable breaks. The time it taktes for the ball to fall halfway to the ground is 1.2s. Find the time it takes for the ball to fall from rest all the way to the ground Homework Equations v=vo + at The...
  49. J

    AP Free Fall Question Solved: Finding Velocity & Time in Vertical Motion

    AP free fall question (solved) Homework Statement I have problem with question b. A hot air bolloon is traveluing vertically upward at a constant speed of 5.00m/s. When it is 21.0m above the ground, a package is released from the balloon. a) for how long after being released is the...
  50. J

    How High Was the Stone When It Started Falling?

    Homework Statement A falling stone takes 0.28s to travel past a window 2.2m tall. From what height above the top of the window did the stone fall? The Attempt at a Solution Vo=?, the velocity at the top of the window a= -9.8m/s^2 t=.28s d=2.2m v=? Vo=(1/2at^2-d)/-t...
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