Free fall Definition and 486 Threads

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. 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...
  2. C

    Velocity after Free Fall and after Motion down an Incline

    I was doing some conceptual problems quickly before moving on to the numerical stuff when I glanced at this answer given in the solutions manual, and it surprised me: Which object has greater speed at the bottom of its fall, object A of mass m dropped freely from height h or object B of mass m...
  3. W

    My First Post: A Contradiction in Simple Free Fall?

    Hello, Let us imagine a solid in a free fall on planet Earth and let us neglect the effect of air resistance on the motion of the solid. According to Newton's Second Law of Motion, since the only force being applied on the solid is its Weight, then its acceleration must be its Weight divided by...
  4. J

    Free fall and slide, gained speed?

    Homework Statement which one would be faster when reached the ground? Homework EquationsThe Attempt at a Solution conservation of energy Pe=Ke mgh=1/2mV^2 for 2-)m*g*cosa*(h/cosa)=1/2*m*V^2 -- V= sqrt(2*g*h) for 1-) V=sqrt(2*g*h) so V1=V2
  5. J

    Is free fall NOT the same as floating in space?

    For many, many years (don't ask), I've been running into the classic example of the local reference frame: the man in the box who can't tell if he's floating free in space, or falling into a gravity well. It occurs to me that if one is in a falling box, a mass released at the top of the box...
  6. gasar8

    Calculating Earth Displacement from Free Fall of 1kg Object

    Homework Statement We release m_o = 1 kg object from h=1m height. How much does the Earth move (x)? I just need the comfirmation if I did correctly? Homework Equations Conservation of momentum: m_o v_o + m_E v_E = 0 The Attempt at a Solution I wrote the energy conservation law as (beginning...
  7. R

    Free falling object due to gravity

    Homework Statement The reason why the heavy stone and light stone fall equally because of the ration of force to mass is same. can you explain it please what is ratio of force to mass is same?. Homework Equations F=ma and F=Gm1m2/r² The Attempt at a Solution As their acceleration is same...
  8. J

    Maximizing Free Fall Distance: Solving for Equal Time Intervals

    Homework Statement A body is falling from a height of 720m. Divide this distance into three parts so that the body would overcome all parts in the same time. P.S (This is translated from a different language) Homework Equations x(t)= x0+V0+at2/2 v(t)=V0+atThe Attempt at a Solution I made an...
  9. A

    How Do You Model Free Fall with Air Resistance in Differential Equations?

    <Moderator's note: Moved from a technical forum and thus no template.> An object with mass 96 kg is given an initial downward velocity −3m/s in a medium that exerts a resistive force with magnitude proportional to the square of the speed. The resistance is 60 N when the velocity is −2m/s. Use...
  10. T

    Time for Free Fall from Great Distances

    The equations of a falling object dropped from a 1000 foot tall building are simple: eq 1 ##s=1/2( at^2)## eq 2 ##v(final)=(2as)^.5## eq 3 ##v(final)=at## where a is the acceleration due to gravity at the surface of the earth s is the height of the building, t is the time it...
  11. B

    Initial velocity of ball B hit a free falling ball A

    Homework Statement A boy release ball A from height 5m from ground at the same time other boy throw ball B vertically upward to exactly strike ball A. When ball B released it was 1m from ground find minimum initial velocity of ball b. Given g=10m/s^2 a) 2m/s b) 3m/s c) 4m/s d) 5m/s Homework...
  12. axer

    Why can't we apply the speed equation in a free fall?

    Hello, so i know in a free fall the acceleration is constant (9.8 m/s2) therefore speed/velocity is increasing.. But I am wondering why we can't use Speed=D/T
  13. Jay Addy

    Why do objects fall at the same speed in free fall?

    This is something I haven't been able to wrap my head around yet. In physics, I've always been told that gravity is a force that ALWAYS works between "objects" with mass. Now, it seems clear to me that if a feather and a hammer were to be dropped at the same time on Earth (without air...
  14. K

    Side kick on a falling object, mechanical energy and work

    If an object with 1kg mass falls free (no air drag), from 100 meters high, and the gravitational acceleration is 9.81, then the mechanical energy will be: 1*9.81*100 = 981 joules. The work the gravitational force does on the object will be: 9.81N*100m = 981 joules. Another object with same...
  15. D

    Free Fall vs Jetpack: Will He/She Stay Afloat?

    There is a random person falling from the sky. He remembers that he has a jetpack. Unfortunately, his jetpack is weak and is only able to provide upward force equivalent to Fg. WILL HE?SHE STAY AFLOAT OR WILL HE?SHE CRASH INTO THE GROUND? What acceleration will he/she hit the ground?
  16. A

    Free Fall quadratic equation problem

    The answer based on the answer key is 3 seconds. I used the quadratic equation to solve for t. My question is how do we know what sign to use when solving for the final value? For this problem, I had to use the negative sign, but I knew that I needed to use the negative sign because I already...
  17. B

    Elevator Free Fall: Understanding the Physics and Sensation of a Cut Cable

    Hi guys, I know this is a really simple question, but I'm just making sure I have this concept down: Scenario 1. An elevator accelerates down at 9.8m/s^2. Scenario 2. The elevator cable is cut. If someone is inside an elevator, scenarios 1 and 2 would feel exactly the same to them, correct...
  18. S

    How can I calculate the depth of a well using free fall and distance equations?

    Homework Statement A stone falls from top of a well, 10 seconds later sound of water splash reaches the top of the well. How deep is the well? g=9.82m/s2, vsound=340m/s , t=10s 2. Homework Equations s=vt , v=a0+at , s=v0t+1/2at2 3. The attempt at a solution I'm stuck. I know the...
  19. Pushoam

    Calculating a bolt's free fall time in an accelerating elevator

    Homework Statement Homework EquationsThe Attempt at a Solution A) W.r.t. Earth's frame, After 2s , velocity of bolt = at = 1.2*2 = 2.4 m/s distance traveled = (1/2) 1.2*22 = 2.4 m Let's say that the bolt reaches the floor at time t. Using s = ut + (1/2)at2 2.4 = 2.4t +(1/2)(-9.8) t2...
  20. D

    Free fall distance with non-constant g

    <Moderator's note: Moved from elsewhere and therefore no template.> I'm trying to calculate the distance of free fall for an object with zero tangential velocity but a given radial velocity at a given height over a given period of time. This calculation cannot assume that g is constant as it...
  21. S

    Can a bullet hit someone while free falling?

    If two people are free falling from the sky at the same (high) speed, at the same altitude, but about 20 meters away from each other, and one of them has a gun and tries to shot the other, do they aim directly at the other person so they get a hit (because the bullet would also be falling), or...
  22. Alexander350

    Why is it quieter to lower your hand when you catch a falling ball?

    If there is a ball falling from a height due to gravity, and you keep your hand still and let the ball fall onto it, it stops suddenly and makes a loud noise. However, if you lower your hand as you catch the ball, like when a cricketer catches a fast moving ball, the catch is almost silent. I...
  23. Charly

    B Why Do Bodies in Free Fall Change Position?

    Why do bodies in free fall change position relative to each other? For instance in a vacuum with no external forces why can an apple fall towards the surface of the earth? If these objects aren't accelerating then are they considered at rest? And in what sense of the term 'rest'. I think I can...
  24. jrp95

    Modeling Acceleration at Impact

    Hi all, Background: I'm working on a project where I am dropping an arduino with an accelerometer from ~100 ft in the air to measure it's acceleration during free fall and at impact. I need to compare my collected data with predicted models. I have the model for free fall (just 9.8m/s^2)...
  25. David Thomson

    Free Fall Arrest: Create Mathematical Model for Safe Thrill-Seeker Experience

    It is recorded that someone has survived a free-fall from an airplane by being lucky enough to land on snow-laden fir trees. My challenge is this: Create a mathematical model which describes the forces at play in order to determine the viability of creating a safe and fun 'thrill-seeker'...
  26. T

    I Radial Proper Dist. Objects Free Fall: Calculating Δs

    If we consider 2 shells in Schwarzschild spacetime their radial proper distance ##d s^2 = \frac{1}{1-\frac{r_s}{r}}d r^2## follows from the metric with ##dt=0## and ##d\Phi=0##. Integrating yields ##\Delta s## as a function of the r-coordinates of the shells. A reference with the formula for...
  27. NoahCygnus

    Kinematic: Problem based on free fall

    Homework Statement "A body dropped from the top of a tower covers a distance '7x' in the last second of its journey where 'x' is the distance covered in the first second. How much time does it take to reach the ground ?" Homework Equations ## S = ut - \frac{1}{2}gt^2## The Attempt at a...
  28. NoahCygnus

    How Long Does It Take for a Ball Thrown Upwards to Hit the Ground?

    Homework Statement "A ball is thrown vertically upward with a speed 'v' from a height 'h' metre above the ground. The time taken for the ball to hit the ground is." Homework Equations ##s = ut + \frac{1}{2}at^2## The Attempt at a Solution...
  29. N

    B How Do Proper Acceleration and Gravity Affect Time Dilation in Free Fall Orbits?

    I had been informed that for objects in free fall orbit no proper acceleration would be measured. https://www.physicsforums.com/threads/stationary-frames-of-reference.899195/page-2#post-5658771 But I also understood it that for objects in free fall orbit gravity time dilation would be observed...
  30. O

    B Mass and free fall speed under gravity

    If mass increases with speed then what is the mass and speed of a particle falling from a large distance into a black hole or onto a neutron star?
  31. E

    Free Fall Experiment: Predicting Ball's Maximum Height and Time

    Homework Statement When throwing a ball, a student has a friend time how long it takes the ball to reach the maximum height. Before they start the experiment, the friend predicts: “If you throw the ball faster, the ball will reach the highest point in less time.” Do you agree or disagree with...
  32. MrGoATi

    Ball dropped down from 5m, what is its speed when it hits the ground

    Homework Statement sportsman jumps at 5m/s velocity from 5m cliff to water. at what speed does he reach water? so given answer is 11.1m/s though in this book there are some wrong answers (I did try other equations and I got right answer but I want to know why I can't get it using this one)...
  33. R

    Free Fall and a Projectile motion question

    Homework Statement 1. A diver jumps from a height of 10m leaving with a velocity of 8m/s find the time for which the diver is in the air and the speed at which the diver enters the water? 2. A ball is launched from point A on a horizontal plane with an angle of 55*. It passes two walls both 2m...
  34. G

    How Does Earth's Longitude Affect Free Fall Equations?

    Homework Statement Solve free fall from height h to the Earth´s surface in the place longitude φ. During solving, Consider gravitation acceleration as a constant for the whole trajectory, so g=constant. (consider a homogeneous gravity field) and variables which are including angular speed ω...
  35. G

    How Is the Coriolis Force Applied in Calculating Free Fall?

    Hi, I would need some help with my homework. I am lost. Solve free fall from height h to the Earth´s surface in the place with geographical width φ. During solving, omit addiction gravitational acceleration to the distance. (consider a homogeneous gravity field) and variables which are...
  36. G

    How Does Coriolis Force Affect Free Fall at the Equator?

    Hi, I would need some help with my homework. I am lost. Solve free fall from height h to the Earth´s surface in the place with geographical width φ. During solving, omit addiction gravitational acceleration to the distance. (consider a homogeneous gravity field) and variables which are...
  37. T

    I Free Fall vs Acceleration: Einstein's Theory Explained

    How does this work exactly? I can understand depending on frame of reference but I read that Einstein stated there is a right way to think about that based on inertial and non-inertial frame of references.
  38. V

    Max Jumping Height in Elevator Descending at Constant Vel.

    Homework Statement I work as a supplemental instructor for an intro physics class. As I was preparing my worksheet for this week I came across this problem. A basketball player can jump to a height of 55cm. How far above the floor can he jump in an elevator that is descending at a constant...
  39. parshyaa

    Time of free fall does depend on mass

    Months ago I have seen walter lewins first lecture on dimensions, there he made a comment that scientist are trying to prove that time taken to reach ground when a object is dropped does depends on mass (in small amount) but it depends on mass, how they have thaught that it depends on mass ...
  40. E

    B Drop Ball Moving: Initial Velocity 0m/s?

    Hi I'm trying to solve a problem but I'm a bit confused about this part: Suppose you are walking at a speed of 2 m/s when you drop the ball that you were holding in your hands. Is the initial velocity 0 m/s? In the textbook it says that initial velocity for dropped objects is 0 m/s but that...
  41. G

    Free Fall and the Accelaration of Gravity

    If I were to throw an object in the air from the ground and it would reach 50% of its maximum height in 2 seconds, how does one find the object's total maximum height and total travel time? This is the last question in my 1D kinematics chapter. I've been successful in resolving my other...
  42. S

    Who Hits the Water First? Investigating Free Fall Bungee Jump Physics

    Two girls are standing on a bridge over a river. One girl falls freely and the other ties a rope to her legs. Both jump at the same time from the bridge. The length of the rope is more than the vertical distance between the bridge and the river so that the rope never becomes taut till she...
  43. F

    B Test of the Universality of Free Fall with Atoms

    I have found an article about an experiment that states that gravity on a small scale doesn't experience quantum effects. Of course the headline has been catchy, so I want to ask about the real importance or relevance of the experiment. Or for short: Do the results imply any consequences on...
  44. centenond

    Free fall does'nt consider weight

    Okay so first of all forgive me if I sound dumb, and forgive my english, is not my primary language. So I know two objects will fall at the same rate if air is excluded, so what I am asumming its that free fall formula is only correct if there's no air, right? So I am a programmer and I want to...
  45. eric_cravin

    Cork flying into air, only acceleration and total time

    Homework Statement Bindi pops the cork off a bottle of champagne. The cork travels vertically into the air. She notices that the cork takes 4s to return to starting position. a) how long does cork take to reach maximum height? Homework Equations I know that a= -9.81m/s/s, and the final...
  46. J

    I Spacecraft Launches: Perigee & Apogee - Why Terminate?

    why spacecraft launches are usually terminated at either perigee or apogee?
  47. J

    I William skinner Machine gravity

    Could someone explain under which principle does Skinner's machine operate? Is it just a free falling mass that's taken back to it initial position by very little input energy, thus generating a constant gradient or potential difference, and generating energy, or is it just storing kinetic energy?
  48. J

    An application of free fall (DE) model to industry

    Could someone tell me an application of the model of free fall to industry or more generally by using Newton's second law and the law of gravitation, construct a model similar to the free fall one, that has an application in industry
  49. RoboNerd

    Understanding Free Fall: Debunking Common Misconceptions

    Homework Statement An object is in freefall on Earth. Which of the following statements is true? A) The object is gaining an equal amount of momentum for each second it is in free fall.B) The object is gaining an equal amount of momentum for each meter it falls.C) The object is gaining...
  50. A

    Fall Rate of Objects: Explaining Why Weight Matters

    Hello - I have a question from a CSET practice exam that I'm having trouble understanding the provided answer. Q Two items are dropped simultaneously from a ten-story building. The items are shaped similarly and are relatively the same weight. Which of the following statements is correct...
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