What is Free fall: Definition and 485 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. brotherbobby

    Catching a loaf of bread thrown vertically at a window

    I start by copying and pasting the problem statement as it appears in the text. Let's have a diagram for the problem. A loaf of bread, drawn in brown, is thrown up from the ground with two different speeds ##(v_0)_{1}## and ##(v_0)_{2}## such that it just reaches the bottom and top of the...
  2. brotherbobby

    Distance-time graph of a ball throw vertically up from a fixed point

    Statement of the problem : I copy and paste the statement of the problem to the right as it appeared on the website. Given below is the graph of the ball as its distance from a fixed point with time. Attempt : Where does this fixed point, say ##\text{P}## lie? Imagine the fixed point lied...
  3. Ineedhelpwithphysics

    Free fall kinematics problem

    I am super stumped at this question, the answer key is telling me 6.78 downwards, i think I'm reading and observing the question wrong. Isn't final velocity 0 so why can't i do 0 = v0 -9.8(0.25) -2.45 = v0 But when I use the second the equation -2 (displacement of door) = v0(0.25) + 1/2...
  4. brotherbobby

    Two balls, dropped with a delay of ##\Delta t##, meet after rebound

    I draw a series of images of the problem situation. In (a), the first ball in green is (just) dropped at time ##t=0##. In (b), the second ball in red is dropped at time ##t=2\;\text{s}##. In (c), the first ball rebounds after a total time of falling down ##t_d##. At this position, its velocity...
  5. Clockclocle

    Compare the ratio of two times t1/t2 in this vertical jump

    Here is my attempt. At ymax the velocity turn to zero so we get time t*=v0/g and ymax=1/2 (v0^2/g). At the height y max, since the velocity at this point is 0, i get another equation y= 1/2(v0^2/g)-(g/2)t^2, this equation could be considered as continuation of first equation. Set ymax/2=1/4...
  6. Clockclocle

    Homework help: Dropping a sand bag from a Hot Air Balloon

    In this situation should my free fall equation contain the v0 of the baloon or I should deny it. Because it seems to me that there is no outer force acts on the sandbag, so the scenario is just the same as I climb to the same height at time t=0 and drop the sandbag at rest.
  7. groetschel

    Object A (in free fall) hits object B (ascending with constant velocity)

    DofA = D0 + 1/2at^2 DofB = vt DofA = DofB, but how do I solve this and get the time when A and B hit?
  8. A

    B Does the density of a liquid affect the braking of an object in free fall when it lands?

    In mine hypothesis I want to slow down free fall for diffrent density objects in liqudies. I have a stone wich i roughly a denisty of 2,7 g/ml and gold with 19,7 g/ml. They have the same size. Liquied glucose has the density of roughly 1,5 g/ml. In my example, I drop at the same time in a 1...
  9. 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.
  10. Darmstadtium

    B Work Done during 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...
  11. 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...
  12. 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...
  13. 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...
  14. 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...
  15. qnt200

    I Weak principle of equivalence (Galileo, Newton)

    Many tutorials that explain the weak principle of equivalence (Galileo, Newton) do not clearly state whether the body is affected by the force of inertia during free fall as a result of the gravitational acceleration of the body. In other words, the question is whether, during the free fall of a...
  16. 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...
  17. 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...
  18. A

    Free fall of solid bodies

    I don't even know where to begin. I assume that the masses are equal.
  19. 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...
  20. Jynku

    Free fall acceleration

    Shouldn't free fall acceleration be constant at -9.8m/s^2 until the object hits the ground and turns zero?
  21. 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...
  22. S

    I If gravity is not a force, what is holding us down?

    OK. Gravity is not a force it is a contraction or curvature of space. I was free-falling and now I hit the ground. Why don't I float through the universe, or go upward instead of still trying to go downward. Because I hit the ground, and now there is no force(like gravity) and my free-falling...
  23. 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.
  24. 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
  25. 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
  26. brotherbobby

    Vertical flight with air resistance

    I suppose the trick in this question is to realize that the drag acts in opposite directions when the ball ascends and descends and that the ball actually takes less time to rise and more time to fall than normally. I make a small sketch of the problem alongside. Attempt : The total time of...
  27. 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...
  28. D

    Atwood's machine 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...
  29. 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
  30. 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...
  31. Selfphysicslearner

    What is wrong with following physics equations? (velocity and acceleration)

    vavg=(Vi+Vf)/2 vavg=h/t then vavg*t=h h=(Vi+Vf)/2 * t Vf=at (Vit+at2)*1/2=h But formula on every resource I found says it should be; (Vit+at2*1/2)=h What mistake did I do ?
  32. J

    G-force experienced by a jumper, using a DE

    We are given that ##v' = \frac{1}{10}v^2 - g##. I tried using implicit differentiation so that ##v'' = \frac{1}{5}vv' = \frac{1}{5}v(\frac{1}{10}v^2-g)## and set this equal to 0. Hence we have 3 critical points, at ##v= 0##, and ##v = \pm \sqrt{10g}##. Calculating ##v''(0)=-120##, we know the...
  33. K

    Does a strong wind slow down your free fall?

    I was wondering do strong wind slow down or has any effect on the outcome of your free fall? Like slower down your impact or help you survive? Hypothetical, you free fall down height of 1,000 feet below are just rocks so hard surface (not water). Basically it should cause death. But let say...
  34. torito_verdejo

    Equations of motion in a free fall with friction

    I'm stack at the very beginning. If I use Newton's second law to find acceleration and integrate until I find the position, I must face $$v(t) = \int_0^t g-\frac{\lambda v}{m} dt'=gt-\frac{\lambda }{m} \int_0^t\frac{\partial z}{\partial t}dt$$ But this last term feels pretty weird. I don't...
  35. archaic

    Free fall time in an accelerating frame of reference

    This is my wrong attempt, the bolt's equation for ##t\geq 2## would be ##y_b(t)=-\frac{1}{2}g(t-2)^2+e(2)+l## where ##e(t)=\frac{1}{2}wt^2## the position of the elevator's floor in the absolute frame of reference. ##d(t)=-\frac{1}{2}(w+g)t^2+2gt+2(w-g)+l## the distance between the bolt and the...
  36. S

    A Gravity on Planets: Does Mass Affect Free Fall?

    My current understanding is that a person falling toward the surface of a planet with no atmosphere, would feel no force acting upon themselves even though they are accelerating relative to the planet. If the mass of the planet suddenly tripled while the person is in free fall, would the person...
  37. brotherbobby

    Sphere and Bar in freefall

    For convenience, I have marked the C.G. of the sphere as ##G_S## and that of the bar only as ##G_B##. The C.G. of the combination is halfway between them, shown by the green ##G_C##. My answer is that the combination will rotate about ##G_C## (centre of the bar) as it falls. I wonder if I am...
  38. Benjamin_harsh

    Why air resistance has less force than gravitation force in free fall?

    Why air resistance has less force than gravitation force in free fall? If Egg is fall from a nest of tree, while falling, it has less magnitude of air resistance than gravitation force. Where net force is not equal to zero.
  39. Z

    B Why do things in free fall accelerate?

    Hello, I have a problem to understand acceleration in GR, objects in free fall move along a geodesic, they are in inertial motion. But observer on Earth can clearly see that falling thing accelerates. What causes the acceleration, when there is no gravititional force? Thanks for answers.
  40. P

    Free fall velocity and distance

    Homework Statement A 0.1 kg nut is thrown by a squirrel off of the top of a 10 m tall tree. It is thrown with an initial upward velocity of 4 m/s and an initial horizontal velocity of 3 m/s. a) How long till it reaches the top of its arc? b) From the top of its arc how long till it reaches the...
  41. SebastianRM

    I What is the gravitational component in the radial direction?

    Hey guys, I reading over Taylor's Classical Mechanics book. Chapter 9, Centrifugal Acceleration Section. In p.346 he mentions that for a free fall acceleration: g = g_0 + Ω^2 * Rsinθ ρ Where its radial component would be...
  42. xpell

    Free fall equations with realistic, altitude-dependent g?

    Hi! I was wondering about an object free-falling to Earth (or wherever) in a vacuum from a very high altitude where g is significantly lower than on the surface: let's say 5,000 km for instance, where g would be 3.08 m/s2 according to the equation gheight = gsurface · (RadiusEarth / (RadiusEarth...
  43. S

    Homework help: Work and Energy, Free fall

    Homework Statement A 200 kg object moves at 10 m/s at 20m (vertically). It falls to a height of 5 m. Find the new speed. Homework Equations vf²=vi²+2ad The Attempt at a Solution vf²=(10m/s)²+2(9.8m/s²)(15m) vf=19.8m/s To find the distance for the new speed I did 20-5, but I'm not sure it's...
  44. hawkeye1029

    Compression of a spring by an object in free fall

    Homework Statement A 2.0 kg object starting at rest falls 3.0 m onto a 4.0 N/m spring. How far will the spring be compressed? m = 2.0 kg vo = 0 m/s2 y = 3 m k = 4 N/m g = -9/8 m/s2 Homework Equations eq1: Fg = mg eq2: Fspring = -kx The Attempt at a Solution [/B] eq1: Fg = mg Fg =...
  45. I

    I Do electrons radiate when in free fall?

    So, I've been reading a whole bunch of different answers to this online. Some people say yes, some people say no. I'm totally confused...
  46. devilish_wit

    I'm stuck This is a combination of dynamics and free fall

    Homework Statement A flat cushion of mass m is released from rest at the corner of the roof of a building, at height h. A wind blowing along the side of the building exerts a constant horizontal force of magnitude F on the cushion as it drops as shown in the figure below. The air exerts no...
  47. vAhmed

    Calculating a ratio in Free Fall motion

    Homework Statement A ball is thrown upward with a speed v 1. The ball reaches a maximum height of y=h. What is the ratio of the speed of the ball,v 2 , at y=h/2, to the initial upward speed of the ball,v 1 , at y=0? Homework Equations I attached a picture. We are currently studying the four...
  48. C

    Radially falling into a Black Hole

    Hi, I have the following problem: Given the 5-D generalization of the Schwarszschild solution with line element: ds^2=-\Bigg(1-\frac{r^2_+}{r^2}\Bigg)dt^2+\Bigg(1-\frac{r^2_+}{r^2}\Bigg)^{-1}dr^2+r^2[d\chi^2+\sin^2(\chi)(d\theta^2+\sin^2(\theta)d\phi^2)] where ##r_+## is a positive constant...
  49. shahbaznihal

    A Rods, Clocks & Free Fall: Metric & Connections in GR

    In Classical GR the metric tensor ##g_{\mu\nu}## determines the length of rods and ticking of clocks while the connection ##\Gamma^{\alpha}_{\mu\nu}## determine the equation of geodesic (the free fall motion of particle). Furthermore, in GR the Levi-Civita connection is uniquely determined by...