Golf balls with drag

[PhilipOakley]

Has anyone seen
http://www.eng-tips.com/viewthread.cfm?qid=245945&page=1

I didn't have time to do a direct mathcad sheet that just 'solves' the laws of motion.


Philip Oakley

[StuartBruff]

On 5/27/2009 10:13:36 AM, philipoakley wrote:
== Has anyone seen
http://www.eng-tips.com/viewthread.cfm?qid=245945&page=1
== I didn't have time to do a direct mathcad sheet that just 'solves' the laws of motion.

Somebody replied last night - just a quick and dirty equation transliteration (apart from a couple of terms where the transliterator obviously couldn't bear to put actual numbers in when a symbol was called for), no finesse at all.

Who know, perhaps the transliterator is considering Mathcadizing it?

Stuart

[ptc-1368288]

On 5/27/2009 10:13:36 AM, philipoakley wrote:
>Has anyone seen
>http://www.eng-tips.com/viewth
>read.cfm?qid=245945&page=1
>
>I didn't have time to do a
>direct mathcad sheet that just
>'solves' the laws of motion.
>
>
>Philip Oakley
_____________________________

The *.PDF is for the recycle bin !

The *.mcd does not treat the problem !

The "free fall" was made available in 3 sheets this last fall [2008]. It is in french as no collb seemed interested after having been posted as a forum problem. I'm too short of time to put it in english, but the maths would be the same. Whatever, the problem has only solution from experimental results and that is the point missed from a profane approach.

jmG

PS: The attached are sourced
and obviously put in Mathcad coding.

[TomGutman]

Bah. Humbug.

Not only is that Matlab stuff too complicated and messy and not suitable for conversion to anything, it is wrong. The analysis is wrong. You cannot break up the Reynolds number into a horizontal and vertical component, nor can you calculate the frictional drag separately for horizontal and vertical components. Because it is non-linear (a V² dependency) the drag must be computed along the actual trajectory and then decomposed into horizontal and vertical components. Not to mention that the assumption of an instaneous change between two coefficients based on the magnitude of the Reynolds number is not likely to be real. There may be a fairly rapid transition, but certainly not instaneous.
__________________
� � � � Tom Gutman

[AlvaroDíaz]

On 5/27/2009 7:21:24 PM, Tom_Gutman wrote:
>Bah. Humbug.
Agree. Drag coefficient (k) is bad evaluating. Also the jump in Cd can be an acceptable estimation if the transition is checked better, or the effects in the ball trajectory.

Regards. Alvaro.

[ptc-1368288]

Pretty clear from my 3 work sheets that the "Golf balls with drag" is wrong, not only incorrect. Wrong from the concept. Reynolds is experimental, if not from experiments then can't just guess or else assumption.

Read again in "Chute libre en Maquette"

"The calculated (terminal velocity) is "experimental" and approximate, but very close to be true. The inaccuracies account for:
1. at the beginning of the fall there is a small period of Stokes fall (friction resistance)
2. the drag coefficient is experimental and there is no exact maths for.
Once those opinions are accepted, the formula for the space traveled is declared "mathematically true", then exact. At this point of having expressed the velocity as function of the space traveled, the interest of the project is to calculate the distance it takes to reach the terminal velocity, then solving for h in "

More in this thread is like a duck:
Duck dines bottoms ups !

jmG