Talk:Free-fall

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[edit] A contradiction in the article!

The first line says: "Free fall is motion with no acceleration other than that provided by gravity, and no deceleration other than that caused by the aerodynamic drag of the object". Then a few lines down it says: "Examples of objects not in free fall: ... Jumping from an airplane" What!? ExitLeft (talk) 00:46, 7 December 2007 (UTC)

Excellent point. I've tried to clean up the intro by distinguising between the technical, physics definition (falling under the influence of gravity only), and the nontechnical, skydiving usage in which drag from the air is also acting. What do you think? Physicsman1965 (talk) 04:55, 30 January 2008 (UTC)

[edit] Michael Holmes

I think its wrong to have his story here. His parachute was open, but entangeled. He had spinn on the parachute. Yes, he had fast vertical speed but far from free-fall. you can see the video here: http://www.dagbladet.no/nyheter/2007/02/13/491864.html (norwegian)

[edit] Czechoslovakia

An anon just ammended the reference to Vesna Vulovic, in what was probably a well meaning attempt to avoid nationallistic bias [1]. However, I suspect the plane didn't blow up over both the Czech Republic and Slovak Republic. Does anyone know the more precise location based on today's boundaries? -- Solipsist 21:51, 11 Jun 2005 (UTC)

Here: Srbska Kamenice. Article updated. Pavel Vozenilek 22:02, 11 Jun 2005 (UTC)

Someone should comform the information provided in this section with the information provided in the Vesna article. They aren't consistent. Rklawton 02:45, 5 February 2006 (UTC)

[edit] Spelling

I've just gone through this article and changed most of the spellings to 'free fall', but I may not have done this right. I did a bit of checking with online dictionaries that suggested the version as two separate words was most common, see for example [2]. More acurately it seems that

  • 'Free fall' - is the noun, the fall of a body within the atmosphere etc.
  • 'Free-fall' - is the intransitive verb, or the act of falling
  • 'Freefall' - not used at all

In general, we should use a consistent spelling within the article. However, this suggests that we should use both 'Free-fall' and 'Free fall' depending on whether it is used as a verb or a noun. We should also consider moving the article to 'Free fall' (I think we are principally discussing the noun). -- Solipsist 19:43, 24 November 2005 (UTC)

I checked with the United States Parachute Association's website. They use "freefall" approximately 98% of time time (out of nearly 300 references). The USPA does not use the hyphenated version at all. Rklawton 02:39, 5 February 2006 (UTC)
Should we create a separate article for "freefall" that refers only to a human falling with nothing more than the wind to offer resistance? Parachutists use the word "freefall" to describe the period between the jump and the open canopy. (see: USPA) Rklawton 20:58, 11 February 2006 (UTC)
I'd say the two are similar enough that it is best to discuss and handle the difference on the same page. If you like, both are in freefall for most of the flight but the later uses a parachute to come out of freefall, whilst the former uses the surface of the Earth :)
Slightly more problematic is the use of Wingsuit flying to control and direct the drag. There is at least one guy who has a suit with webbed flaps between the arms and legs so that he can glide horizontally a little - at which point the parachutists are arguably not in freefall. -- Solipsist 08:46, 26 May 2006 (UTC)
Lots of people use wingsuits. Even skydivers aren't sure what to call skydiving with a wingsuit. To wit, world records. It doesn't seem very sporting to count wingsuit records against non-wingsuit records. However, both wingsuit fliers and freefallers need their parachutes to survive in the end. Rklawton 13:38, 26 May 2006 (UTC)

[edit] Shayna Richardson Accident

The mentioned accident was not a good example in this case. I read on http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=1973796 that she opened her reserve parachute, however it failed to inflate properly. Such accidents (hard landings because of parachute malfunction) happen from time to time in skydiving and this particular one was not something very unique or at least not as unique as the Yugoslavian girl that survived plane crash. Shayna had partially inflated parachute what reduced her terminal velocity and thus it was not a pure free fall. I suggest removing this part from this article.

The video makes it clear she wasn't in freefall, so I removed the reference. Rklawton 20:51, 11 February 2006 (UTC)

[edit] Tiny Broadwick

I was going to add a See also to Tiny Broadwick, an article I just started, based on Googling up some research... Actually, that article could use some expansion, so if anyone is interested, please make some changes. -HiFiGuy 19:39, 1 March 2006 (UTC)

[edit] Problem with the drag equation

The equation is derived from the assumption that the acceleration is dependent on mass and gravity (m * g) whereas in reality in only depends on gravity (g). Secondly, there is a problem with the latex implementation. I'd rather someone with a better math/physics background fix the equation before I attempt to myself. --216.170.141.157 22:51, 25 May 2006 (UTC)

I've moved this comment to the bottom, because Wikipedia convention is to add new comments to the bottom of the page. Now, I was under the impression that free-fall under constant gravity without drag is only dependent on gravity, but free-fall with drag is dependent on the shape, size, and mass of the object as well, which is why a lead ball falls faster than a feather. I can't confirm the correctness of the equation, but I can say that acceleration with drag is NOT dependent only on gravity. TomTheHand 23:31, 25 May 2006 (UTC)
Righto, but remember, we're mixing apples and oranges. That is, there are two different definitions of freefall in play here. One relates to skydiving and the other relates to physics. Let's just make sure the article is clear on the difference - and keeps them separate. Rklawton 06:24, 26 May 2006 (UTC)

There also appears to be an inconsistency with the "real" drag equation, where the drag is proportional to the square of the velocity, not as given here where it is proportional to the velocity.

The first equation of the "With air drag" section is wrong. The first member should be a force but is instead an acceleration (the derivative of the velocity). It should be m * ay = -(k * v) + (m * g). Sorry for my bad English, but I'm not a native speaker.

What is this constant number 5000 of Vy=...? How did you get it? --Shoons 15:12, 15 May 2007 (UTC)

The drag equation is:

Fdrag= 1/2 ρv2CdA

The drag coefficient is dimensionless. Consider that the object moving through the fluid is displacing the mass of fluid at a rate of ρ*A=m/d. The right hand side of the eq. has the dimensions of a force:

energy/distance = F*d/d = m*a = dp/dt

Note that dp/dt reflects that the force is proportional to the velocity and the mass of the fluid accelerated out of the way. The mass accelerated is contained in the swept volume/t:

(V/t)(1/V)m = (A*d/t)(1/V)m = m/t

So the drag force can be seen as a momentum transfer to the fluid per time, and is proportional to v: F=v*m/t The proportionality to v2 appears in the drag eq., because of the proportionality of the force to m/t. Spunkets1 (talk) 21:35, 19 February 2008 (UTC)

[edit] Freefalling and parachutists

I would say 'freefalling' in the parachutist sense is not freefall. It is 'dropping' or 'falling'. It doesn't hurt until you land :). Plenty of air-resistance acting on you. Whereas freefall would when there is no net force acting on you. ie: when forces are balanced (ie: zero-g, gravity is countered by your orbital speed). If you were outside the Sun's gravity well, you might be effectively in free-fall... I guess nowhere are you outside of the reach of gravity. But the lack of sensation of forces pulling on your mass == freefall.
-- ~ender 2005-03-13 12:00:MST

  1. Note that zero-g is independent of gravity. A mass is in zero-g when no force other than gravity is acting on that mass. You, the reader are presently prevented from experiencing zero-g for significant periods because your chair is firmly pushing on your butt. Jumping up will temporarily place you in zero-g – until you hit something. Rklawton 22:52, 3 June 2006 (UTC)
  2. That's one way to use the word freefall. It might even be a good definition for physicists. However, here in the skydiving world, freefall means just you and the wind. Rklawton
  3. The science community might consider skydivers not as freefalling but in a maneouver called "aero braking." Because they can change roll, pitch, and yaw as well as horizontal and vertical velocity (within limits), skydivers often think of themselves as "body pilots" or "in flight." Rklawton 22:52, 3 June 2006 (UTC)
  4. To prevent confusion, and since skydivers aren't actually in freefall as defined in science, and since skydivers (see the USPA website) spell freefall differently, I think we should create a separate freefall article for skydiving. The two can point to each other to aid disambiguation. Any takers? Rklawton 22:52, 3 June 2006 (UTC)

Splitting the article might be an alternative, but it might be better handled by having separate sections on this page and discussing the destinctions in the different use of the word. -- Solipsist 08:47, 4 June 2006 (UTC)


The article should be split so the definitive definition of free-fall (physics) is a body experiencing solely the force of gravity (with other relevant sections) and a separate article for sky diving freefall and its relevant sections

I think we're really talking about the difference between a technical physics definition and a nontechnical usage among skydivers. I've tried to make that distinction clearer in the introduction, and it might be desirable to make that distinction clearer throughout the existing article, rather than splitting the article into two. On another technical note, 'zero-g' refers to a situation in which the force of gravity is vanishingly small (far away from any massive body such as a planet, star, or asteroid). What one experiences in free fall (technical sense) is apparent zero-g (or apparent weightlessness). One experiences all of the indications of zero-g, even though (ironically) one is falling precisely because gravity is acting. One does not experience apparent weightlessness in free fall (nontechnical, skydiving sense) after the first few moments of falling, by the way. Physicsman1965 (talk) 04:45, 30 January 2008 (UTC)

[edit] Record free fall speed

I have found multiple sources saying different speeds at which Kittinger fell. This USAF site says it was 714 mph and this Time magazine article says it was 614 mph. I assume one is a typo since they're only off by one digit. Which would people suggest we use? This obviously has implications in many other articles too.

--W00tfest99 19:02, 19 February 2007 (UTC)

==It's 614... close to the speed of sound at that altitude and enough for Kittinger to claim he broke the speed of sound. At 714, he would have clearly done so. Rklawton 20:59, 19 February 2007 (UTC)

[edit] Photos don't match article

Quick question ... there are two photos on the page. The first is a photo of skydivers, but the article states: Jumping from a plane, as there is a resistance force provided by the atmosphere. Why then is there a photo of parachutists saying they are in free fall? Second, there is a photo of Joseph Kittinger saying it's a record free fall, yet the article says Eugene Andreev holds the record. Should these photos be removed? Pgrote 14:40, 21 September 2007 (UTC)

First, I believed clarified.
Second-- Keep. Kittinger made the higher jump, but the drogue chute lowered his terminal velocity and provided stabilization. Andreev had no such chute, so he fits the term free fall as used by skydivers. MMetro 18:57, 28 October 2007 (UTC)

[edit] Acceleration Due to Gravity Versus Acceleration Due to Other Forces

I'm probably just thick, but when you are in free fall, accelerating under only the influence of gravity, you feel weightless (zero G).

On the other hand, when your acceleration is caused by any force other than gravity, you feel a sense of weight (G forces).

This keeps me awake at night.

What gives?

125.161.130.92 (talk) 21:51, 17 November 2007 (UTC)H&T