# Free fall Definition and 54 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. ### 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...
2. ### 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...
3. ### 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...
4. ### 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...
5. ### 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.
6. ### 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...
7. ### 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 ?
8. ### 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...
9. ### 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...
10. ### 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...
11. ### 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...
12. ### 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...
13. ### 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...
14. ### 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...
15. ### Free fall, earth displacement

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...
16. ### 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...
17. ### 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...
18. 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...
19. B

### Elevator free fall

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...
20. S

### Free Falling bullet duel

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...
21. ### 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...
22. ### 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)...
23. ### 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)...
24. ### 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...
25. ### B Dropping object

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...
26. ### 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...
27. ### 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...
28. ### I Perigee and apogee

why spacecraft launches are usually terminated at either perigee or apogee?
29. ### 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?
30. ### 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
31. ### Question on free fall.

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...
32. ### Fall Rate of Objects

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...
33. ### Centrifugal force on Earth and deviation of free falling obj

Centrifugal force due to rotation of the Earth has among its effects the deviation towards the equator of a ball falling from height ##h## vertically on Earth. I do not understand what is the inertial explanation of this phenomenon. Once the ball is released there is no centripetal force that...
34. ### Balloon and ballast

Homework Statement A balloon is ascending at an speed of 13 m/s. At 300 m from the ground a ballast is drop from the balloon. Find the maximum height the ballast reach. My doubt is: When the ballast is drop ¿it starts falling inmediately?. The solution of the problem implies that the ballast...
35. ### Why people float inside free falling airplane

in science shows , an airplane made to fall freely under gravity has its passenger floating in mid air i understand weightlessness is due to 0 normal reaction by floor on person but since both passenger and plane have same aceleration due to gravity what might be reason for relative separation...
36. ### Free Fall Problem

Homework Statement Calculate the length of time it would take for an object to fall 10.0m if g were one sixth the value of Earth's g. g=1/6(-9.8)= -1.633333333 m/s^2 a=-1.633333333m/s^2 displacement=10.0m[down] Homework Equations Maybe one of the big 5 kinematics equations? Or maybe...
37. ### Free Fall and Final Velocity

Homework Statement The Drop Zone drops riders 27m from rest before slowingthem to a stop. How fast are they moving before they start slowing down? vf=? vi=0, di=27m[up], df=om, displacement=27m[down], acceleration=9.8m/s^2[down] Air resistance is negligable Homework Equations...
38. ### Free fall acceleration

Homework Statement Can free fall acceleration be determined by dropping a marble through a single photogate? The CPO timer attached to the photogate can measure the time it takes for the marble to pass between the arms. Knowing the diameter of the marble enables one to calculate the speed. If...
39. ### Is it possible for a person in motion to fall over a ledge?

The facts are that the person is 183cm, 82kg, meaning his center of gravity is about at 105cm, he was running towards a railing of a balcony that is 108cm high, and allegedly hit the railing then fell over. Is this physically possible?
40. ### What does an accelerometer measure?

Hi I'm confused about what an accelerometer actually measures. I downloaded an app that reads out the data of the accelerometer in my phone in all three dimensions. If I lay it flat on a table, it says something around 9.81 in the z direction and something around zero in the x and y directions...
41. ### Proper Acceleration In Accelerometer ?

Hi guys, I'm working on my project with accelerometer. I know that accelerometer measure specific force or proper acceleration in general by deflection of proof mass. Proper acceleration is relative to free fall which could be analogy that proper acceleration is the relative acceleration...
42. ### Differential equation for grav, boyant and drag force

Homework Statement So there is a falling object, you have to take into account the boyant force, the pull of gravity and the drag force A time dependent distance equation is what we're looking for Homework Equations Fd=CdApav2/2 Where Fd is the drag force Cd is the drag coefficient A is the...
43. ### Conservation of Energy - Max height WITH Air resistance

Homework Statement A ball (m=0.7kg) is dropped from a height (h=30m). The air resistance force is given by the formula F=kv^2 where k=0.0228 and v is the ball's speed. The ball bounces after a perfectly elastic collision. Calculate the maximum height the ball reaches after the collision...
44. ### Simple pendulum in a lift

Homework Statement This is a 'random discussion' that I had today with a student; it is not out of a textbook, nor does the solution carry any weight at all (pls excuse pun).[/B] A simple pendulum is happily swinging back and forth attached to a pin in the wall of the lift, where the pin is...
45. ### What is the definition of "free fall"?

1. "An object is in "free fall" when the only force acting upon it is gravity". 2. Is gravity in this case singular or plural? Is the acting gravity the resultant force of all bodies in the universe? 3. In theory, my own bodys gravitational force is acting on the object and thus it's not...
46. ### Vessel of water under free fall

When a Vessel of water is under free fall and there is a hole in the side of the vessel, why does no water come out of the vessel? (its given in my textbook that pressure exerted on sides of vessel is zero. But what does the horizontal force have to do with the vertically acting force due to...
47. ### Free Fall - Calculating Origin/Release

Homework Statement In this problem I don't know the release point/origin of a dropped ball. I do however have a stroboscopic photograph of it moving through my frame of reference. In my frame of reference it moves 2.0m in 4 seconds. Now, I am suppose to figure out how far above the first...
48. ### What is the velocity just before the body touches the ground

Homework Statement A body is dropped from a height ##h## with an initial speed 0, reaches the ground with a velocity of 3 km/h. Another body of the same mass was dropped from the same height ##h## with an initial speed 4 km/h. The second body will reach the ground with what velocity ? Homework...
49. ### Properties of a Free Fall

Say a person was descending at constant rate of 1m/s while holding a ball. Then, without stopping, the person dropped the ball which assumed a free fall. Would the ball assume an initial velocity of 0m/s, or would it start at the one 1m/s that the person is traveling? If anyone can, please...
50. ### Observing black holes inside black holes

Can an observer, freely falling into a black hole observe another black hole, falling with him, after crossing horizon? I assume one should be, as for freely falling observer nothing special happens, when he crosses horizon. But just wanted to double-check.