# What is Freefall: Definition and 117 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. ### I Newton's 2nd law for an object in free fall

From inertial frame, object in free fall has just one force mg. So Fnet=non zero, but acceleration =0, isnt this in "fight" with Newton 2law? Is object accelerating or not ? Can I say, yes object is accelerating but object dont "experience" acceleration?
2. ### I What is the proper time of a vertically moving inertial clock?

Hi. I am looking for an equation for the round trip elapsed proper time of a clock that is initially moving vertically straight up with a given initial velocity, reaches apogee and then returns to the starting location under gravity. I would like to use the external Schwarzschild geometry of a...
3. ### 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...
4. ### I Precession of a gyroscope in freefall

Imagine I have the following gyroscope: This gyroscope has been spun up with significant angular momentum and rests on a platform below it. It's offset at an angle and so I've drawn the R vector from the axis of rotation. So the only force being applied right now is gravitational force...
5. ### I In Freefall orbiting Jupiter versus Earth

I know that in Earth, an astronaut feels weightless in orbit but actually is not. The astronaut would not feel his own weight until he actually stands on a floor where his feet point towards the Earth as the Normal Force is the perception of weight. So, in Jupiter, where g ~ 25, an astronaut...

The freefall wiki entry wiki Freefall has an analytic solution for freefall distance in a gravitational field, but ... it doesn't seem to work ... at least i can't get it to work ... here is my MATLAB program to test it ... clear G=6.7e-11; % gravitational constant m^3/(kg*s^2) mEarth =...
7. ### Circular and linear freefall

Does circular freefall of an object involve cancellation of gravitational and inertial forces, as it does in linear freefall?
8. ### Understanding Exercise 3 and 8 in Freefall and Motion Law

I need help with the exercises attached in the pictures. Basically, exercise 3 is already solved but I need some help understanding every subpoint (for example, at a) how did we get to 0=H -g* tAO/2 , I know it's from the motion law and vA=0, but why is y(t)=0?). And I tried solving ex 8, but I...
9. ### Escape velocity and gravitational freefall

Is an object with escape velocity in gravitational freefall?
10. ### The Indeterminacy of Problems with Multiple Friction Interfaces

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...
11. ### A How Long To 'FreeFall' Into TON 618 From ISCO

So I'm trying to help someone get an idea of the 'scale' of some of the most massive black holes, but, I'm at best a laymen when it comes to this stuff. Because ISCO for a non-rotating black hole is just 3 times it's radius, and I can calculate apparent arc radius from ISCO, I could tell them...
12. ### Air resistance - freefall and horizontal projectile motion

We have two identical balls sitting at the same height. One of them is released without applying any force (it falls freely) and the other one is given a non-zero horizontal velocity. Which of them will hit the ground first? The force of air resistance is proportional to the square of the...
13. ### Comparing Crushing Forces: Human vs. Fly

Homework Statement Hello All, I might be at best HS level physics understanding but I’m quick study and need guidance. I am in a debate with someone who thinks a body can be crushed to the point of dust. I’d like to know if a comparison can be made, basic ratio: Human crushed by a building at...
14. ### Freefall v Jetpack: Will He/She Stay Afloat or Crash?

Homework Statement 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...
15. ### 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. ### Force in Center of Mass frame equaling zero

Homework Statement Suppose I have particles with masses m1 and m2 , both are in freefall: Then , looking at the center of mass coordinates , I know that the sum of momentums of masses m1 and m2 in the center of mass coordinates is equal to zero : P1c + P2c = 0 so now I know that the total...
17. ### I What Is the Formula for the Position of a Mass Falling Towards a Planet?

Question: Finding the closed formula s(t) that gives the approaching position of an inertial mass to a planet Supposing the mass initially stationary, and far enough and for long enough that it is NOT possible to consider the gravity as constant while it moves closer and closer. Said in a...
18. ### Time taken for free falling objects to travel a set distance

The time taken for a free-falling object to fall a set distance (on earth) is, according to Wikipedia, described by the equation: t = √(2d/g). Why is the distance doubled in this equation/ how is this derived?
19. ### Terminal Velocity of a Cylinder Freefalling Through a Fluid

Hello :) I am an engineer and I am trying to analyse a system which basically contains a cylindrical body free-falling through a body of static water beginning with zero velocity. I am ultimately trying to find what the velocity of the object would be at a depth of 20m. In order to do this I...

Homework Statement Pretty simple question, just checking for confirmation. It was a small question at the beginning of a summative test, a rock was dropped off of a bridge and we were asked to graph the kinetic energy over time. Homework Equations 1/2mv^2. The Attempt at a Solution I...
21. ### Free fall with + and - Vinitial

Two objects thrown from a cliff. One with + vinitial (upward) One with - vinitial (downward). Does the one with + vinitial not reach a greater height and thus have a larger vf upon hitting the ground since it falls farther and therefore is subject to gravity longer?
22. ### Escape Velocity = Freefall from Height of One Radius?

I was doing some calculations using the escape velocities from Earth, Moon and Mars. Then by chance I calculated the velocities attained when an object was "dropped" from a height of the radius on each of these bodies, assuming the acceleration due to gravity remained constant during the fall...
23. ### Freefall problem of a diver jumping horizontally upward

Homework Statement A diver jumps vertically straight up off of a platform 3 meters above the surface of a pool below. The diver hits the water and comes to rest in 0.80 seconds after traveling through 3.6 vertical meters of water. (See the diagram below). Assume the acceleration of the diver...
24. ### Finding Freefall Acceleration on a planet

Homework Statement On a certain planet, which is perfectly spherically symmetric, the free-fall acceleration has magnitude g = g0 at the North Pole and g = λ g0 at the equator (lambda is between zero and 1). Find g as a function of theta, the colatitude angle. Homework Equations \vec{g} =...
25. ### Travelling to Mars at constant velocity? Weightless?

If I'm traveling on a spaceship at a constant velocity (say 10000 m/s) towards Mars will I feel weightless, or will I feel nearly weightless because I will still be slightly affected by gravity? I know that when astronauts are in the ISS they feel weightless because they are in a constant...
26. ### Calculate Real Freefall | GM/x^2 Integral

We always consider the accelaration as a constant thing, while calculating the freefall problems. What if we try to calculate the real. I mean taking the accelaration GM/x^2. I tried it but i could not handle that integral(Just graduated from high school). I would be happy if you reply. Thank you
27. ### How Does Projectile Motion Affect a Ball Thrown Upward from a Building?

Homework Statement You throw a ball vertically upward from the roof of a tall building. The ball leaves your hand at a point even with the roof railing with an upward speed of 15.0 m/s; the ball is then in free fall. On its way back down, it just misses the railing. Find (a) the position and...
28. ### Projectile Motion Homework: Solving for Time, Position, and Velocity

Homework Statement A ball is thrown vertically upward with an initial speed of 19.6 m/s from the top of a building 44.1 m tall. Assuming that there is no air resistance. a.) At what two times is the ball 10.0 m above its starting point? b.) What is the position of the ball at t = 5.00 s? c.)...
29. ### Finding the Initial Velocity of a Basketball Shot Using Freefall Equations

Hello first time posting in the Physics forum! 1. Homework Statement A varsity player is attempting to make a shot. The ball leaves the hands of the player at an angle of 50 degrees to the horizontal at an elevation of 2 meters above the floor. The skillful player makes the shot with the ball...
30. ### Is Freefall Really Not Accelerated Motion? Debunking Common Misconceptions

According to this video, freefall isn't accelerated motion and is actually stationary. In other words, you aren't moving in freefall:
31. ### Freefall to rolling with no slip

Homework Statement A uniform sphere with know mass m, moment of inertia I, and radius Rs is traveling through free space with initial horizontal linear velocity v1 and rotational velocity w1. It then makes tangential contact with a horizontal surface and instantaneously starts rolling without...
32. ### Freefall of an object in Space (towards earth)

Hi guys, My professor showed us in class how to find the final velocity of an object as it hits the the atmosphere of earth(Rf=6.37e6) and I think he might have made a mistake. I have been trying to solve the same problem but I get different answer than the one my professor showed in class. The...
33. ### Satellite in Space: Why Freely Falling?

Q1 Why does a satellite(or any space capsule etc) moving in a stable circular orbit around Earth behaves like a freely falling body?? Q2 Why do the astronauts in these capsules are said to be in weightless condition?? i m not much convinced with the solutions to my doubts so i would appreciate...
34. ### Solving for Angular Acceleration & Speed of Rod in Freefall

Homework Statement Consider a uniform rod of mass 12kg and length 1.0m. At its end, the rod is attached to a fixed, friction-free pivot. Initially the rod is balanced vertically above the pivot and begins to fall (from rest) as shown in the diagram. Determine, a) the angular acceleration of...
35. ### How Do You Solve the Freefall Catching Problem in Physics?

Freefall "catching" problem Homework Statement I have been having trouble understanding this physics problem and am so confused as to how I would even start. Two friends are playing "catch" on a level playing field. At t=0 the are at x = 0. At t = 0, the catcher is run-in in the positive...
36. ### Construct Freefall DE Model for Felix Baumgartner

Homework Statement One of my classes involves constructing a differential equation to model the freefall of the red bull sky diver Felix Baumgartner. I need to construct the correct differential equation to find v(t) and y(t) at any given time t. As stated above, I need to take the two...
37. ### What Is the Angular Speed of a Falling Ruler at 30 Degrees?

Homework Statement A ruler stands vertically against a wall. It is given a tiny impulse at θ=0∘ such that it starts falling down under the influence of gravity. You can consider that the initial angular velocity is very small so that ω(θ=0∘)=0. The ruler has mass m= 250 g and length l= 25...
38. ### Freefall prob that's been bugging me.

This problem has been bugging me for a while... If a stone thrown from a bridge strikes the water 10.0 m below after 1.70 s, what was the stone's initial velocity?My first attempt was to use Δy = vyi(Δt) +0.5(g) (Δt)^2 because I understand that the time to fall is dependent only on gravity. I...
39. ### Solve Quadratic Equation for Cliff Height

1. At t=0, a stone is dropped from the top of a cliff above a lake. Another stone is thrown downward 1.6 s later from the same point with an initial speed of 32 m/s. Both stones hit the water at the same instant. Find the height of the cliff. 2. d_{1}=\frac{1}{2}gt_{1}^{2}...
40. ### How High Does the Flowerpot Rise Above the Window?

Homework Statement A cat spots a flowerpot that sails first up and then down past an open window. The pot is in view for a total of .50s and the top-to-bottom height of the window is 2.00m. How high above the window does the flower pot go? I was trying to help one of my friends with...
41. ### Identifying Freefall: Analyzing Graphs for Acceleration

Homework Statement So I am doing my lab, when I realize that I am not sure where the freefall occurs. I collect the data for a ball tossed in the air, and using a vernier motion detector, I found the graphs for displacement, velocity and acceleration (attached). second peak) Homework...
42. ### Find position function of freefall with air resistence ODE

Homework Statement An object of mass ##5##kg is released from rest ##1000##m above the ground and allowed to fall under the influence of gravity. Assuming the force due to air resistance is proportional to the velocity of the object with proportionality constant ##b=50##N-sec/m, determine the...
43. ### Freefall in a Newtonian gravitational field

1) The problem statement : For this problem, We use Newtonian Mechanics. We are placed in a geocentric frame of reference. An object (of which the mass is irrelevant for this problem) is released into the Earth's gravitational field at an altitude p(0) with no velocity whatsoever. The...
44. ### Newton's second Law of Acceleration, Inertia and Momentum, Freefall

Okay, we have one-thousand pounds; at sea level, and a feather. We elevate them to a thousand meters and support them on a platform. All of which is in a vacuum. We remove the platform, they both hit the earth; the limiting surface; at the same time. Newton's second law suggests that this is due...
45. ### Sliding Ramp and Freefall problem

I typed this up on MP's Whiteboard, but the tutors were taking way too long to respond: (question is also attached) Edit: Units are in meters. Questions asks to Find h (small h defining the height of the ramp). The exact moment the object leaves the ramp, it would have components Y=gsin(30) and...
46. ### Effect of freefall on hydrostatic/atmospheric pressure

I was thinking about Walter Lewin's thinking question: "If an astronaut were to try to drink from a sphere of floating juice through a straw in a capsule pressurised at 1 atm, could he drink effectively?" The answer to this is yes because of the atmospheric pressure. But it got me thinking...
47. ### Understanding the Relationship between Kinetic and Potential Energy in Freefall

Homework Statement You drop a ball from a high balcony and it falls freely. Does the ball's kinetic energy increase by equal amounts in equal time intervals, or by equal amounts in equal distances? Explain.Homework Equations KE = 1/2mv^2 PE = mgy Conservation of energy: Emech = KE + PE; Esys =...
48. ### Time and height in a freefall problem

Homework Statement A marble fell from the height h and covered the last 196,2m in 4 seconds. How long was the marble falling? What height was it falling from? Homework Equations s=s_{0}+v_{0}t+\frac{at^{2}}{2} v(t) = v_0 + at The Attempt at a Solution In the first equation...
49. ### FreeFall motion Assumptions in proving

Homework Statement a stone is thrown vertically upwards with a speed of u metres per second. a second stone is thrown vertically uppwards from the same point with the same initial speed but T seconds later than the first. prove that they collide at a distance (4u^2-g^2T^2)/(8g) metres above...
50. ### Freefall Arrow Problem: Finding the initial speed and maximum height

1. An arrow is shot vertically upward with an initial speed of 25 m/s. When it's exactly halfway to the top of its flight, a second arrow is launched vertically upward from the same spot. The second arrow reaches the first arrow just as the first arrow reaches its highest point. What is the...