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. nadja

    I Relativity: the Special and General theories

    "I stand at the window of a railway carriage which is travelling uniformly, and drop a stone on the embankment, without throwing it. Then, disregarding the influence of the air resistance, I see the stone descend in a straight line. A pedestrian who observes the misdeed from the footpath notices...
  2. F

    Admissions Profile evaluation for astronomy Phd applicant in the fall 2023 cycle

    I will apply for a Ph.D. in Astronomy in the fall of 2023. I want to have a realistic evaluation of my profile to see if I am over-ambitious or not. I think I am out of reach for the "big four" universities. I will donate money to two of them only and will be targeting other top schools...
  3. ejacques

    Calculating Train Deceleration: Kid's Free Fall Time

    I think, since the train is decelerate the kid will fall off at free falling. the time for that is: y=0.5*9.8*t2 ⇒ t=√(2*y/g)=√(2*3/9.8)=0.8sec. Now i think i need to find what is the distance the train is doing in this time, but i can't figure this out.
  4. Darmstadtium

    B Is the Definition of Work Done Applicable to Free Fall?

    For example, if a ball is from a certain height, the work done is 0 as there is no change in total energy the Ef =Ei. However, there is a constant force applied over a certain distance, suggesting work is being done. Which aspect am I forgetting/missing? Or is it that the definition of work done...
  5. T

    B Does Mass Matter in Free Fall?

    Hello. I read on Wikipedia that when a body is in free fall from zero mass, its mass does not matter and two bodies of different weights will fall at the same speed. I think this is not correct. If I consider that the bodies are in a weightless state and the gravitational force will act on them...
  6. davenn

    Stargazing The Happy Fall Day for Meteorites

    Happy Fall Day, Chelyabinsk, Russia 15 Feb. 2013 4 small meteorites, affectionaltely known as Chelly Peas ( that are about the size of a pea) The glass is from windows in Chelyabinsk that were broken by the shockwave blast
  7. M

    I Do equipotential lines fall on the equiprobability contours?

    For 2D charge distribution ρ(x,y)=Ne PDF(x,y), where PDF is the normalized probability density function with its peak on (0,0) and has standard deviations σ x. and σ y. Are the contours with the equal probability "PDF(x,y)=const" the same as the equipotiential contours?, I tend to think that...
  8. C

    Free fall with a partial time provided

    I'm stuck on this problem, I've tried to follow techniques for similar questions, namely I seem to be struggling with these questions where I have to use an equation inside an equation. I've attached photos of my process so far, but obviously, I'm not getting the right answer because what I'm...
  9. C

    So confused by these multi-step questions, free fall related:

    Tried making many squiggles, I don't understand the concept of finding a distance or position based on a time for part of the flight. I have 2 other similar questions and I haven't been able to make any progress on any of them. I attached a photo of my scribbles, which are all obviously...
  10. C

    I Do objects of differing mass fall at the same rate in a magnetic field?

    Gravity isn't a force in the strictest sense of the word, yet magnetism is exactly that: a force. As is strong, EW, etc. Therefore, it's possible that the more massive magnetic object gets drawn to the center of a magnetic source at a faster rate than the less massive magnetic object. Discuss!
  11. Trikenstein

    I Ball free fall 100m at equator, where is the landing spot?

    We have a weekly fun random chat to break from the routine of WFH. A science quiz poped up. There is no consensus on the good answer. We need 3rd party opinion. You are at the equator, dropping a steel ball into a dry well, the depth is 100 meters, the mass of the ball is 1kg. The starting...
  12. D

    B Free Fall in Curved Spacetime: Does Minkowski Spacetime Exist?

    This topic has been discussed in the past on this forum, however there is one point that seems to be unclear. One example of the setup is the following: The universe is at a stage where all the matter is concentrated in a single black hole, except two spacecraft s A and B that orbit it far...
  13. T

    Engineering project: Harvesting energy from natural water fall

    - design of a micro-turbine based on different scenarios of waterfalls - build a system that involves a battery for storing power - test in the lab I have attached a image. I know the image is not very detailed but wanting some advice on this situation. I have done some water calculations on...
  14. Lahouircha

    B Hi, I'm learning physics -- Why do things near me not fall toward me?

    Hi, I'm learning physics because I love it and I have many questions I'm struggling to understand the difference between laws of motion and universal gravitation Question 1 : For example : every object applies a force to another object like the Earth is attracted to the sun, so is the monitor...
  15. Godot_

    I Does Dark Matter Fall into Black Holes?

    Does dark matter(DM) fall into black holes(BHs)? IMHO it should... ...as it does interact with normal matter gravitationally. Once it's done so, does it add to the BH's mass? Again, IMHO it should. AFAIK it does have mass... Would that "quasi-convert" it to normal matter? ...after all, this...
  16. S

    Reasoning/evaluation: Free fall motion with constant acceleration

    My guess is that I could compare it to the time interval of the free fall motion(stage2). Would that be enough to let it make ‘sense’? As we know that stage 1 has an acceleration of 16m/s^2 and free fall one of 9.81m/s^2. Then.. is it sufficient to reason that the time needed to complete stage...
  17. A

    Understanding Free Fall: Newton's Laws and Gravity

    I don't even know where to begin. I assume that the masses are equal.
  18. SpaceThoughts

    I Will the spinning gyroscope make the plumb fall slower?

    When winding a bike wheel up in an elastic double string in the ceiling, and then let the wheel spin vertically, it unwinds more slowly than if it was not spinning. I tried it. But it if a spinning disk is placed in a solid construction like this (photo attached) , and can only rotate...
  19. jtbell

    Mini road trip: fall festival fun

    On Saturday, I took advantage of a crisp sunny day to visit two festivals in small towns a couple of hours' drive from home. Stop 1 My first stop was at the Central Railroad Festival in the town of Central, which is nowhere near the center of South Carolina. It's way up in the northwest corner...
  20. R

    B Free fall floating in a closed spaceship near a gravity source

    Floating inside a closed spaceship, no windows, not knowing if I'm free falling near a gravity source or far away from any gravity source, are there any experiments that can be made, to determine if there is a gravity source near and if there is such an experiment, to determine the gravity...
  21. Jynku

    Is Free Fall Acceleration Constant Until An Object Hits the Ground?

    Shouldn't free fall acceleration be constant at -9.8m/s^2 until the object hits the ground and turns zero?
  22. B

    B How long it takes the Earth to fall halfway to the Sun--ellipse method

    There's a classic physics problem that is: If Earth is orbiting the Sun at 1 au from and is suddenly stopped. How long does it take to fall into the Sun (neglecting the size of the Sun/Earth)? I know that a clever way to solve this problem is by using degenerate ellipses and an object...
  23. DaveC426913

    B Can you fall below the horizon on an expanding balloon?

    This scenario came up (as a dream) in a sci-fi novel (Robert J. Sawyer's The Terminal Man). Two people of height h, initially within sight of each other, at d distance apart , on a huge balloon of radius r. As the balloon expands, they might or might not lose sight of each other over the...
  24. L

    A slanted cylinder full of liquid about to fall

    The cylinder will cease to be in equilibrium when the sum of the torques on the cylinder calculated with respect to the rightmost point of contact of the cylinder with the plane will be unbalanced. Now, the liquid is homogeneous and the cylinder has negiglible mass so the forces (normal force of...
  25. Rubberduck2005

    Bead sliding on a Vertical Circular Loop versus in Free Fall

    I can evaluate the first beads motion easily A to B is -2Rj considering the point B as y=0 the motion of the bead will be -gt^2/2+2R=0 which implies t=2√(R/G) , this is ok but what I am struggling with is A to C I can see that the angle between the beads weight and it's negative normal force...
  26. B

    Question about APS DNP fall meeting

    Hello! I would like to submit an abstract to the APS DNP meeting this fall and I need to choose a category for my talk. I see that they have a series of Mini-Symposiums and my talk would fit both in a non-Mini-Symposiums but also in a Mini-Symposium (it seems like Mini-Symposiums overlap a lot...
  27. AHaHaCiK

    A question about why gyroscopes fall slowly

    why when the gyroscope work for a short time, it will fall down slowly. I know that the system loses the energy by work done by friction between the wheel and its axis, but I don't understand how this makes the gyro drops. I think the friction makes the wheel spin slowly, and precession...
  28. A

    Rocket problem -- separated fuel tank in free fall

    I know that this should be a very simple problem, but I don't understand how to solve it without knowing the height at which the tank is separated from the rocket. I will be very grateful for any hint.
  29. M

    Is acceleration still equal in the presence of air resistance?

    I remember being told that heavier things fall at the same rate as lighter things when everything else is equal. But this guy does a demonstration of a Xenon balloon falling faster than a Neon balloon. Why? Also an overloaded plane may not be able to fly, but it has the same aero dynamics, it...
  30. R

    Free fall question -- Dropping a pebble into a well to figure out the depth

    t=7s v=340m/s v=v0-gt 340=v0-9.8x7 v0=408.6 d=d0+v0t-0.5gt^2 d=0+408.6x7-0.5x0.8x7^2 d=2620.1m this is what I've done but apparently is incorrect, not sure why or what the proper method is
  31. M

    Determining g by free fall with light gates -- assumption analysis

    the only way i can think of changing the method is by using 2 light gates instead of 1, calculating the velocity through each and using this to get an average velocity, but not sure how this would help
  32. P

    Analyzing the Fall of a Chain: Problem 103 of 200 Puzzling Physics Problems

    My attempt: At first, only a small part of the chain has fallen through. Let that part have mass m, speed v, and length x. Suppose the chain has a mass per unit length of u. To accelerate a small length of chain on the table to speed v, Force needed = v dm/dt = v (dm/dx) * (dx/dt) = uv^2...
  33. J

    I How Long Does it Take to Fall into a Black Hole?

    Gratings The following is an example of a question that I have been battling to get my mind around for some time: How long, in gravity-free time (Tᴓ-time), would it take for a stationary, one kilogram, point-mass to fall directly towards a non-spinning, accretion-disk-free, singularity in a...
  34. E

    Classical The motion of cats and stuff in free fall

    Hey everyone, where can I learn fairly rigorousoly about continuum mechanics and specifically about how to map between motions in the configuration space ##\mathcal{C}## and motions in the shape space ##\mathcal{C} / SO(3)##? I would like to model the general motion of deformable bodies with...
  35. J

    Angular Momentum Problem: Torque after fall

    I know how to get to the answer but that's what is confusing me. To find final velocity I multiply the acceleration by the time the object fell. Then multiply the velocity by the mass to get momentum. Now the angular momentum is r x p. Since the initial angular momentum was 0, this was also...
  36. G

    I Why does an object initially at rest begin to fall?

    Motivation for why I'm asking this: I'm trying to better understand why an object that is initially at rest with respect to a massive body will fall simply by virtue of the curvature of spacetime. If it were moving through space with respect to the Earth initially, I could see the curved path...
  37. D

    What is the free-body diagram for a massless pulley in free fall?

    Hi. First of all i have a question regarding a simple Atwood's machine. The pulley has no mass and the string has no mass and is inextensible. If one pulley is suspended from a fixed support and it has 2 masses ; one at either end of the string. If i construct a free-body diagram of the pulley...
  38. Lars1408

    I Why Do Objects Fall Along Spacetime Ripples?

    When people try to explain how gravity works, the following example is constantly used . However, I don’t understand how this explains HOW gravity works. By using this example, gravity itself is used as a bias to explain how gravity works. How can explain gravity by saying “things fall along...
  39. M

    B Can You Fall Into a Black Hole? Exploring Time & Decay

    It takes infinite amount of time to cross the event horizon from an outsider's perspective. But black holes eventually decay from Hawking radiation. So if you wait long enough a black hole won't exist anymore, as it would have decayed into nothing. The in-falling observer witnesses infinite...
  40. docnet

    B Do things that fall into black holes ever reach the singularity?

    A Paradox of the black hole is that GR states the stationary observer experiences time dilation, while the inflating observer experiences no time dilation. By the time the infalling observer reaches the event horizon, an infinite amount of time passes for the other frame of reference. But...
  41. NovaBlast

    What's the terminal velocity of a Boeing 737 in free fall from 12.496km

    Say that all the engines of a boeing 737 failed while it was 12.496km in the air and fell into freefall, what would its terminal velocity be and how long would it take to hit the ground
  42. F

    B Why don't electrons fall into the nucleus?.

    The first result to this question in Google gives this: "An electron in an atom spreads out according to its energy. The states with more energy are more spread out. All electron states overlap with the nucleus, so the concept of an electron "falling into" or "entering" the nucleus does not...
  43. A

    How much deceleration is reasonable for a free fall impact?

    Hi, Hope this is the correct forum for this kind of question. I am doing an explicit finite elements simulation of a tank, weighs around 7.5 Kg with internal parts, falls from 1 meter. Since I never had a validation of such an experiment I am trying to understand if the numbers are right. I...
  44. A

    Why do gyroscopes not fall down?

    he said torque is in direction into the board,but this torque don't have upward commoment so what keep gyroscope to not fall down because mg pull him down??so waht is is force which oppose to gravity?? i understand that torque into the board cause gyroscope rotating in cricle(gyroscope...
  45. Tiago Carita

    How to calculate forces involved in a small fall

    Hi Guys, first things first I’m Tiago -= Introduction to my Many questions =- I work as Inventor in several projects of small scale, doing mechanisms, 3d printing, or building them cutting, welding, using my Lathe or sending to laser cut, bending or (when lucky) sending to a local CNC, I design...
  46. N

    Time it takes for the rocket to fall down

    The first part I can answer. However, the answer to the second one differs from the one in the answer sheet. 1) The rocket first travels gaining speed (a=40m/s^2) and then after the fuel burns loses speed due to g=9.8 m/s^2. Thus, Hmax= h1 (traveled with a=40) + h2 (traveled with -a=g=9.8)...
  47. Tomer Aman

    B Why Does Matter Fall to Center of a Mass? Explained

    Hi Guys. I have a question about General Relativity. If, according to GR, Mass curves Spacetime and gravity is simply matter falling into that curveture, why does all matter fall equally regardless to their spatial position on the mass. For example, why do people in let's say Australia fall into...