Author Topic: Top E Planes  (Read 6834 times)

Offline GScholz

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Re: Top E Planes
« Reply #90 on: January 18, 2014, 01:53:32 AM »
That's quite an answer for a rhetorical question.  :lol

Because you were referring to FLOOB's post about gravity, your "rhetorical" question gave the wrong impression. Gravity accelerates all objects equally regardless of mass.

So when it comes to how gravity affects objects...

So if I have a 1 lb ball and a 10 lb ball and I want to give them equal acceleration do I apply the same amount of force to both or does the 10 lb ball require more force given it's greater inertia?

... is wrong. The answer is: No! ;)


However, to counteract the gravity on those objects you'd have to apply a force equal to their respective weight. I.e. 1 lb vs 10 lb.
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Offline FLS

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Re: Top E Planes
« Reply #91 on: January 18, 2014, 02:32:09 AM »
Gravity accelerates objects of different mass at the same rate of acceleration. In order to do that the force is necessarily proportional to the mass.

Offline GScholz

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Re: Top E Planes
« Reply #92 on: January 18, 2014, 02:54:10 AM »
Gravity accelerates objects of different mass at the same rate of acceleration. In order to do that the force is necessarily proportional to the mass.

No. According to general relativity, gravity is an attribute of curved spacetime instead of being due to a force propagated between objects. There is no gravitational acceleration, in that the proper acceleration of objects in free fall are zero. Rather than undergoing an acceleration, objects in free fall travel along straight lines (geodesics) on the curved spacetime.
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Offline Badboy

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Re: Top E Planes
« Reply #93 on: January 18, 2014, 10:23:20 AM »
All of this is why the language of physics is mathematics, not prose.

The relevant equation of motion was posted a long way back by, I think, Badboy:  a = g - D/m.  You don't have to argue about terminology.  The equation says it all.

A PhD and 25 years experience teaching this to College students and we might as well be discussing fairies at the bottom of the garden :rolleyes: 

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Offline BaldEagl

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Re: Top E Planes
« Reply #94 on: January 18, 2014, 12:43:05 PM »
A PhD and 25 years experience teaching this to College students and we might as well be discussing fairies at the bottom of the garden :rolleyes: 

Badboy

Do fairies fall faster in a vacume and if so which works best, Oreck or Hoover?
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Offline Brooke

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Re: Top E Planes
« Reply #95 on: January 18, 2014, 01:45:50 PM »
The fairy force is transmitted by farions.  CERN is looking for those after they fully nail down the Higgs boson.

Offline Brooke

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Re: Top E Planes
« Reply #96 on: January 18, 2014, 01:50:59 PM »
I love you guys. :)

(Image removed from quote.)

Head now to Eden.  Yay, brother.

Offline Badboy

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Re: Top E Planes
« Reply #97 on: January 18, 2014, 03:49:05 PM »
Quote
What got me mostly into fairies is that I've been finding lots of fairy evidence...

I'm Lydia and I'm a fairy scientist.

http://www.youtube.com/watch?v=akk5EvTMGKo

A young lady with a bright future  :aok

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Offline BaldEagl

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Re: Top E Planes
« Reply #98 on: January 18, 2014, 05:04:59 PM »

http://www.youtube.com/watch?v=akk5EvTMGKo

A young lady with a bright future  :aok

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Or abject failure and a life of drugs and alchohol.
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Offline bustr

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Re: Top E Planes
« Reply #99 on: January 18, 2014, 05:07:48 PM »
Too bad we cannot attribute it to Casimir force.
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Offline J.A.W.

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Re: Top E Planes
« Reply #100 on: January 18, 2014, 10:35:46 PM »
But what about the effects on/of a zoom climb into a stiff headwind? ( L.O.L...)
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Offline Badboy

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Re: Top E Planes
« Reply #101 on: January 23, 2014, 12:37:05 PM »
Quote
Nope.  Wrong.  With the same air resistance both objects will fall at the same rate, regardless of their mass.  Galileo supposedly did an experiment by dropping two balls of differing weights from the top of the leaning tower of Pisa, and both balls hit at the same time.

Galileo is often cited in theads like this one, and almost always in support of fuzzy logic regarding what happens to aircraft during a dive or a zoom. While it is not certain that Galileo actually carried out this experiment, if he had he would not of obtained the results that are widely reported. Just out of curiosity I investigated this a little more. I carried out the calculations in two different ways, firstly by writing the equations of motion as differential equations and solving them by direct integration and also by writing a high frequency simulation and comparing the results.

Firstly I used the calculations to verify the experiment I posted earlier (scroll up to see the video) and then to make predictions about what would have happened if Galileo had carried out the experiment. Assuming Galileo really wanted to see the influence that weight had on falling objects it makes sense that he would have used two similar objects of different weights and cannon balls would have been an obvious choice. Picking them as far apart in weight as possible, so that any difference would be highlighted is also an obvious choice, and in those days 6lb and 36lb iron cannon balls would have been available. If dropped from 183ft above the ground, when the 36lb ball struck the ground the 6lb ball would still be 1ft 4 inches in the air. Sine the 36lb ball was only just over 6 inches in diameter, a difference of 1'-4" should have been easy to see, if not so easy to measure.

But if only Galileo had a taller tower. If the same two cannon balls were dropped from the Empire State Building which is a little less than seven times taller, when the 36lb ball hit the ground, the 6lb ball would still be 48ft 5 inches in the air. Which means the heavy ball would have landed while the lighter one was just passing the windows on the 5th floor... Galileo would certainly have noticed that :)

Perhaps Galileo did spot the difference, which may be why he never described the experiment himself.

The fact is that if we want to know how aircraft perform in a dive or a zoom Galileo's alleged experiment does not help us. Newton on the other hand was born the same year that Galileo died, and Newton's laws are much more helpful.

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Offline DaveBB

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Re: Top E Planes
« Reply #102 on: January 23, 2014, 01:01:24 PM »
They do not teach that anymore.  When the two balls were dropped, the slightly heavier ball hit first.  But it was not of enough distinction that the observers below could tell.  Source: High School Physics class, year 2000.
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Offline LCADolby

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Re: Top E Planes
« Reply #103 on: January 23, 2014, 01:35:22 PM »
Did Galileo ever drop anything which had powered flight?
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Offline Badboy

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Re: Top E Planes
« Reply #104 on: January 23, 2014, 02:24:17 PM »
But it was not of enough distinction that the observers below could tell.

Not a convincing explanation because I think most people could spot a 1'-4" difference, particularly since the balls were a lot smaller than that, so it would have been quite noticeable.

Even with the ping pong balls my students used, falling just over 8ft the difference was 4 to 5 times the diameter of the balls. It is easy to see the heavy ping pong ball pulling ahead in the video, it would have been much easier to see the heavy cannon ball pulling ahead in Pisa because the drop would have taken longer and the gap would have been four times bigger.     

I suspect the difference is minimized in high school deliberately to help make explanations easier/simpler. Unfortunately that can cause the sort of confusion we have seen here. 

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