What is Falling: Definition and 1000 Discussions

In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on it.
An object in the technical sense of the term "free fall" may not necessarily be falling down in the usual sense of the term. An object moving upwards might not normally be considered to be falling, but if it is subject to only the force of gravity, it is said to be in free fall. The Moon is thus in free fall around the Earth, though its orbital speed keeps it in very far orbit from the Earth's surface.
In a roughly uniform gravitational field, in the absence of any other forces, gravitation acts on each part of the body roughly equally. When there is no normal force exerted between a body (e.g. an astronaut in orbit) and its surrounding objects, it will result in the sensation of weightlessness, a condition that also occurs when the gravitational field is weak (such as when far away from any source of gravity).
The term "free fall" is often used more loosely than in the strict sense defined above. Thus, falling through an atmosphere without a deployed parachute, or lifting device, is also often referred to as free fall. The aerodynamic drag forces in such situations prevent them from producing full weightlessness, and thus a skydiver's "free fall" after reaching terminal velocity produces the sensation of the body's weight being supported on a cushion of air.

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  1. B

    I Falling through the event horizon of an evaporating black hole

    I have heard that an person falling toward a black hole would 1) start to "freeze" from the viewpoint of an outside observer as the infalling person's (call him Bob) time dilation slowed Bob's time to a crawl, and 2) from Bob's viewpoint it would seem that he simply falls through the horizon...
  2. Kekkuli

    I Falling into a massive black hole is not necessarily noticeable

    I find it interesting that the more massive the black hole, the weaker the fall acceleration at the distance of the Schwarzschild radius - that's why you wouldn't necessarily notice anything special in the event horizon.
  3. X

    Stokes' law and falling sphere method

    In dire need of help, someone please explain the correct method for this, if its not possible what should i write in the conclusion for this?
  4. Q

    Understanding the Risks of Second Impact Syndrome in Youth Concussions

    A male, 173 cm, 69 kg, faints, falls backwards, his fall is stopped a bit because he falls with his left arm against a cupboard in the bathroom, this happens when he is about 45 degrees with his body compared to the ground, the bathroom has tiles but there is a little flimsy mat to stand on...
  5. MatinSAR

    Distance as a function of time for two falling stones

    I am aware that this question is very simple and basic. Using ##y(t)=y_0+v_{0,y}t-\frac {1}{2}gt^2## we can find distance as a function of time: ##|y_1-y_2|=|y_0+v_{0,y}t|=-y_0- v_{0,y}t## I assumed the downward direction to be negative. So as I wrote ##D(t)=-y_0- v_{0,y}t##. It tells that the...
  6. dwinkley

    Calculating Velocity Components and Slope for a Falling Rock in a Tunnel

    all i could accomplish was calculating the distance between P and the ceiling in a horizontal line(6)
  7. T

    Can Falling in Love Increase Longevity? Psychology & Science Explained

    Hi again all, hope you are all doing great and enjoying the spring as well as nice weather. This is sort of a continuation thread of my falling in love thread here that I posted a while back but with a new question witch is: Can I get the same effect to live longer by falling in love, having sex...
  8. C

    I How to Calculate force exerted on a falling body?

    I'm curious about impact on falling object, so i have taken initiative to solve this problem. I considered only force on the falling object would be its weight and taken F=mg. With only limited data m=.25kg and drop height h=1m. Pondering on this consideration practically, it will have more...
  9. Drakkith

    I Speed of Two Falling Ladders (Veritasium Video)

    Just saw this Youtube Short by Veritasium. The idea is that two identical chain ladders are dropped at the same time. One hits a table shortly after release, while the other continues to free fall. Curiously, after the bottom of the first ladder hits the table, the remainder still in free fall...
  10. phos19

    Falling stick problem (no friction): What is the kinetic energy?

    Since there is no friction : $$ m \ddot{x} = 0 $$ (no x motion).For the kinetic energy , I've tried: $$ K = 1/2 I_{cm} \dot{\alpha}^2 + 1/2 m v^2_cm = 1/2 I_{cm} \dot{\alpha}^2 + 1/2 m \dot{z}^2$$ . Giving me a weird expression , shouldn't the kinetic energy just be half the the moment...
  11. epenguin

    B Disk with holes falling on water

    Just yesterday evening I saw a video of a few minutes where metal disks with holes in them were let fall into a basin of water.The water went up in twisted columns and made the most astounding and beautiful patterns. I thought I would show it to other people who might be interested - but I have...
  12. Bl4nk

    Distance travelled by a falling body

    If (a) is correct, the answer would be 34.3m. If (b) is correct, the answer would be 9.8m. I want to know exactly which one is meant by the question and the reason behind that. Personally i think its a.
  13. J

    Elevator falling and bouncing back from a spring

    I don't understand the difference between part c and d. After compressing the spring, the elevator bounds back and moves before coming to rest in both cases. What is the difference? Thank you.
  14. H

    I What Would it Look Like to Fall into a Black Hole?

    There are a number of videos of simulations of this. They all end with complete blackness. This seems wrong to me because light is concentrated by the black hole. There should be more light closer to the center. On second thought I guess it is OK. While the observer would encounter more...
  15. Z

    Forces on a rope when catching a free falling weight

    If I am not wrong, F = 2*10*9.81*4/0.2 = 3924N (0.2m considering 5% stretch in 4m long rope)
  16. Melbourne Guy

    Are we predisposed to run along the line of a falling tree?

    We have trams in Melbourne, and this weekend I watched a pigeon on the tracks fly up and along the route as the tram came along, being hit by the windscreen (it survived, no worries). Yet it could of flown up and across and escaped because the tram was higher than it was wide. It prompted the...
  17. S

    Work done on a falling elevator by a spring + gravity

    I don't understand what I have done wrong in part (c) I have the initial velocity for the second part of the motion and have the final velocity zero and then the net work done is W_mg + W_Fs and the actual answer for x is 2.37m Could I get some help/tips please, thanks in advance. Here is my...
  18. kuruman

    Insights How to Model a Magnet Falling Through a Solenoid

    [url="https://www.physicsforums.com/insights/how-to-model-a-magnet-falling-through-a-solenoid/"]Continue reading...
  19. M

    Cylinder Falling from Unwinding String

    I need help with this homework question and I'm blanking out. Can anyone help me to answer this question correctly.
  20. vytrx

    Finding speed of a falling brick using distance and the acceleration of gravity

    Since the brick has fallen 30m and the acceleration of gravity is 10m/s^2 the brick would have fallen 3 seconds speed of brick would then be 30/3 leaving the answer at 10m/s?I am new to physics and this question has left me stumped
  21. P

    B How to calculate torque on a body falling freely through the sky?

    if a body is pivoted at a point it is quite easy to calculate the torque as we know the axis of rotation. but, if a body is under free fall and we apply a force of F Newtons at a distance of x from its centre of mass , then how do we determine the axis of rotation?
  22. Distern

    I Collision when a falling tank impacts the surface of a lake

    I'm writing a paper on the movie realism of the A-team movie. The basic situation is that the guys are falling inside a tank with terminal velocity into a lake. I'm stumped on how to calculate the force that is created on impact, though I imagined it being done with some kind of pulse equation...
  23. Tea_Aficionado

    A block falling onto a spring (SHM related question)

    EDIT for clarity: I solved the question, just asking for if the explanations make sense and if the mechanical energy is considered to be conserved before and after the collision due to reasons listed below the photo. I hope this image is readable (grr, scanner is janky). I'm guessing the...
  24. BadgerBadger92

    B Is the Earth falling into the sun from gravity?

    Is the Earth getting closer to the sun from gravity?
  25. M

    I Measuring Light Reflection in a Black Hole

    To keep things "simple", the black hole is 1E30 kilograms. The statite (stationary satellite, blue) hovers above the hole at a fixed location (twice the Schwarzschild radius from the singularity) by tremendous acceleration. The statite drops a probe (green) that begins to fall toward the hole at...
  26. mopit_011

    B Air Gun Sighted at a Falling Target Demonstration

    So in class today, we were talking about how if you fire a bullet aimed at a falling target and release the target and the bullet at the exact same time, they will surely collide. I asked if air resistance (since it’s not a constant force) wouldn’t affect the collision and my teacher didn’t have...
  27. O

    I Magnet falling though copper pipe

    I do not fully understand why a falling neodymium magnet is decelerated in a vertical copper pipe. It is usually explained by Lenz's law, two induced currents generate an upward force that counteracts the force of gravity. (link) However, I assume this upward force has to be generated by the...
  28. Father_Ing

    Falling and sliding stick (David Morin)

    In the solution for question ##(a)##, it is written that the equation of translational motion for the center of mass is ##N-mg=ma_y## Why ##N## is also included inside of the equation? In my opinion, the rail does not exerting force (N) to slow down the mass' acceleration. Instead, the purpose...
  29. Iwanttolearnphysics

    About KE and PE of a stone falling down a tube filled with oil

    This question does not have numbers, so I'm stumped. Here's my thinking. (I), the gain in KE is less than the loss in GPE is correct according to the key, but I think I don't understand this conceptually. Can you ask me questions to make me think about this a bit more? I can't even form...
  30. Iwanttolearnphysics

    About Kinetic Energy of a ball falling vertically and bouncing up

    Hello again. I don't believe there are rules about posting twice in a day. I'm not a student and I answer Physics questions as a hobby, but I've only just started learning, so please help me out. I'm answering IBDP Physics questions. Here's my thinking: KE is not a vector quantity, so it's...
  31. sigurdfromnor

    (Movement Homework) What is the speed of a marble falling on the moon?

    Sorry for the bad english. This might sound stupid but I am pretty new the physics and i can't seem to find what formula to use on this problem when only the mass, gravity and height of the fall is given. and i can't find a similar problem in the book, could someone give me any pointers? Thanks...
  32. G

    I Falling into a Black Hole: Blueshift Questions Explored

    I am under the impression that an outside observer would see things redshifted as the person they are observing approaches the event horizon. So, it seems reasonable that someone from inside the black hole would see incoming light blueshifted. Is this inaccurate? Why or why not? If it is...
  33. V

    Hinged rod rotating, falling and hitting a mass

    Assuming no friction anywhere, no drag and perfect inelastic collision Using conservation of mechanical energy i can determine the rotational speed of the rod right before collision occurs. mgh=1/2*i*w^2 center of mass falls 1/2*L so we have: M*g*1/2*L = 1/2*(1/3*M*L^2)*w^2 Solving for w...
  34. Danimal

    B Object falling through highly compressed air question

    If you had a tube a couple of miles long filled with very compressed air, say 6,000 PSI, would an object you dropped in it fall very slowly? Even a heavy object like an anvil, how long would it take to drop?
  35. A

    I Falling in an O'Neill Cylinder

    So I'm working on a project that involves the design of an O'Neill Cylinder, and there was a consideration that I had never made before. Say you are in a cylinder that is generating enough force for 1G in its spin. This means that while you are spinning, the motion means that your body is being...
  36. Rikudo

    Why is the tension in a falling chain not equal to ρgy?

    Firstly, There is something I want to clarify. When the system starts moving, parts of the chain that still lies on the table, which have mass ## \frac {(L- y_0)M} {L}##, will be pulled by the force that the hanging chain's weight exert,right? If yes, then : As far as I know, the formula ##F=...
  37. timotola

    I Drawbridge falling before caught by rope/cable - Max force

    Hi, I'm currently looking into the forces exerted on a cable if the cable was to go from slack to taut due to a falling object that is pivoted about a lower hinge - such as a drawbridge but instead of slowly lowering, there is slack in the cable causing the bridge to freely rotate about the...
  38. P

    B How do I express the force of me falling 33 feet onto concrete?

    I weight 90.7kg. I fell 10.05m landing on soild concrete. how do I express the "power of my impact? in G-force? A relitive weight? I am self taught in very basic physics after a high school education.
  39. A.T.

    B Falling Cat - Rotation with Zero Total Angular Momentum

    I made a new version of the falling cat video, with narration. It explains how cats turn around while having zero net angular momentum during the fall:
  40. S

    MHB Momentum of Falling Ball X & Ball Y: A Physics Puzzle

    Ball X has mass 0.03kg. It falls vertically from rest from a window that is 30 m above the ground. Ball Y has mass 0.01kg. At the same time that Ball X starts to fall, Ball Y is projected vertically upwards from ground level directly towards Ball X. The initial speed of Ball Y is 20 m/s...
  41. G

    Velocity-distance graph for a freely falling body

    My reasoning: Gradient of graph = v/s = t t increasing therefore gradient increasing So graph B The answer is C.
  42. U

    Falling Tower Problem: Watch How to Solve It in This Video

    I actually have no clue. Found a video that demonstrates the problem: Can someone help pls?
  43. C

    Particle falling radially into a black hole

    I've been stuck starting anywhere with this. I need to finish this class for graduation and i'd like a safety net of a passing grade with this.
  44. L

    A Can falling factorials be a Schauder basis for formal power series?

    We usually talk about ##F[[x]]##, the set of formal power series with coefficients in ##F##, as a topological ring. But we can also view it as a topological vector space over ##F## where ##F## is endowed with the discrete topology. And viewed in this way, ##\{x^n:n\in\mathbb{N}\}## is a...
  45. Z

    EMF induced by a magnet falling through a coil

    I've been told that if you drop a magnet through a coil the induced emf and flux graphs would look like this: I understand that when the bar magnet is in the middle of the coil the emf induced is zero as flux change in top and bottom is in opposite directions but why is effective flux maximum...
  46. A

    Why is m*dv/dt 0 in the Falling Chain Problem?

    I have seen the solution for this problem but still there are some things I do not understand and would like clarification. In the equations below I understand that we use the chain rule on m and v but what I don't understand why m*dv/dt is 0, I don't think is because the acceleration of dm is...
  47. F

    I Issue about the percentage of falling of height of Likelihood

    I have currently an issue about the height at which the projection of 1 sigma edges in 2D contour should intersect the associated Likelihood. Here a figure to illustrate my issue : At bottom left is represented the joint distribution (shaded blue = contours at 2 sigma (95% C.L) and classic...