F=MA

[xmo1]

Just a short question:<br />How can F=MA when A requires some F?<br /> <div class="Discussion_UserSignature"> <p>DenniSys.com</p> </div>

 

[vogon13]

Methinks doth answer involveth the calculus.<br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br />F=MA describes an instantaneous state, if I infer your point correctly you are outside of that condition.<br /><br /><br /><img src="/images/icons/smile.gif" /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[igorsboss]

It can also be seen as an equivalence relationship...<br /><br />For example, if you ever observe mass accelerate, you know the net force on that mass ...even if you can't directly observe where the force is coming from.

 

[CalliArcale]

Or to put it another way, the fact that A requires a certain amount of F is exactly the point of F=MA. <img src="/images/icons/wink.gif" /> If an object with mass M falls on your head and consequently slows down by A kilometers per hour, then force F is applied to your noggin, and you can figure out what the force is by multiplying M by A.<br /><br />Or, for more practical purposes, if you want to fire a cannonball so it's going a certain speed, multiply the mass of the cannonball by the desired acceleration to figure out how much force needs to be applied, which will tell you how much gunpowder you need to pack into the cannon. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[mrmux]

My physics teacher taught us to remember formulae by giving them funny - and preferably filthy - acronyms.<br /><br />I will never forget 'F My A' as long as I live...

 

[vogon13]

Bad boys r our young girls behind victory garden walls.<br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

Calli - Hi!<br /><br />I assume F=MA means Force equals Mass times acceleration. [Like Newton, I prefer words over symbols]<br /><br />Well, can you or someone put numbers to F=MA in the example of the acceleration of expansion of our universe?

 

[drwayne]

Note also that F = ma is not in fact the general relationship. That is<br /><br />F = dp/dt<br /><br />where p is momentum, and dp/dt is the time rate of change of the momentum.<br /><br />This is not entirely a semantic point, you have to use this relationship for something like a rocket, in which the mass of the vehicle is not constnat.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[vogon13]

Why I mentioned calculus. And as you recall, I don't do math. Arithmetic on occasion.<br /><br />It's important for me to be able to sniff out dangerous math up ahead.<br /><br /><img src="/images/icons/wink.gif" /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[newtonian]

drwayne - Thanks for the added detail.<br /><br />Can you attempt an answer to my question as to what numbers to punch in for the acceleration (and momentum during time) of the expansion of our universe?<br /><br />Since energy is converted to mass, and mass into energy, in our universe, I assume the mass of our universe, like the rocket, is not constant???<br /><br />Could loss of mass be one reason for acceleration of expansion???

 

[drwayne]

I am not a cosmologist, just a dumb ol' country boy rocket scientist / physicist / court jester. <img src="/images/icons/smile.gif" /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[dlee0708]

<i>Bad boys r our yong girls behind victory garden walls. </i><br /><br />I remember this one as<br /><br />Bad boys r our young girls but Violet gives willingly.

 

[drwayne]

Thats the resistor code I remember.<br /><br />There is also the spectral sequence<br /><br />Oh Be A Fine Girl Kiss Me Right Now Smack<br /><br />or its lesser known version<br /><br />Old Beer And Fast Girls Keep Richard Nixon Smiling<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[igorsboss]

The expression f=ma is from Newtonian mechanics. Newtonian mechanics stipulates a static universe. Relativity is expressed as gallilean transformations.<br /><br />The extreme conditions present at the start of the universe, and the expansion of the universe, both violate Newtonian mechnics. You need a bigger hammer to explore these questions.<br /><br />I believe the expression f=dp/dt is valid in a wider range of conditions, particularly at high speeds.

 

[newtonian]

igorsboss - What do you mean by "a static universe?"<br /><br />Clearly, Newton believed in the laws of motion - in fact helping discover and refine these laws.<br /><br />Are you assuming Newton believed our universe is a closed system thermodynamically?<br /><br />Remember, Newton believed in God and the Bible - which would mean creation involved input of energy (Force) from outside the system at creation - at least, that seems reasonable to me.<br /><br />I'm all ears, though.<br /><br />I am currently researching the development of astronomy on the general theme of static vs motion in our universe - for example, how Galileo, Newton and Aristotle differed on how or in what sense stars were "fixed."<br /><br />Here is one tidbit relevant to thread theme:<br /><br />"He [Aristotle] took for granted the action of friction because he would not alliow the seminal idealization of a body moving through a void (" nature abhors a vacuum"). Thus, Aristotle was misled into equating force with velocity rather than, as Sir Isaac Newton was to show much later, with (mass times) acceleration." - The New Encyclopedia Britannica, 1989 print edition, Macropedia, Volume 16, page 764.<br /><br />Note that Aristotle believed the stars and planets were fixed to celestial spheres.<br /><br />In contrast, Newton rejected Aristotle's model and discovered how earth and celestial masses were fixed by gravity (in a sort of ether, similar to the actual properties of space with its virtual particles, etc.).<br /><br />Newton believed in the Bible, which stated in 1513 BCE:<br /><br />(Job 26:7) 7 He is stretching out the north over the empty place, Hanging the earth upon nothing;<br /><br />Note the Newton discovered what this nothing is: gravity. Though, with his theory of ether, did not realize how empty space was - at least that is what I think so far - I am still researhing - please feel free to add input to modify my take on this.<br /><br />While gravity does bind some objects, like earth - other gravitational

 

[igorsboss]

<font color="yellow">igorsboss - What do you mean by "a static universe?"</font><br /><br />A universe which is neither expanding nor contracting, so that Euclidean geometry holds. This condition was violated during the expansion period.

 

[newtonian]

igorsboss - I see. Well, I know Newton realized that two bodies with mass at a constant distance would be attracted by each other's gravity.<br /><br />If I remember correctly, Newton deduced that stars must lie at very great distances so as to make this attraction and resulting motion imperceptible by telescope.<br /><br />While Newton believed in the Bible, I do not know if he noticed Isaiah 40:22, with our heavens expanding like a stretching fine gauze or cloth.<br /><br />If he did notice, then he likely believed our universe is expanding - but I do not know.<br /><br />I am still researching these things - please feel free to post anything you have found on this.

 

[igorsboss]

<font color="yellow">he likely believed our universe is expanding</font><br /><br />Whether Newton believed it or not, universal expansion is not accounted for in the Newtonian model of physics. Points in space don't move.<br /><br />Another way of looking at f=ma is as <i>the definition of inertial mass</i>:<br /><br />Mass is the constant of proportionality between force and acceleration. Further, zero (net) force is equivalent to zero (net) acceleration.

 

[newtonian]

igorsboss - Newton did believe in universal motion - a point I suspected for a long time (e.g. my disagreement with Bobw on what Newton meant by fixed stars):<br /><br />Britannica (1989) under Newton, subheading universal gravitation, discussing Newton's discoveries as recorded in his Principia, states of Newton:<br /><br />"The law of universal gravitation, which he also confirmed from such further phenomena as the tides and the orbits of comets, states that every particle of matter in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centres." - "The New Encyclopedia Britannica, 1989 print edition, Macropedia, volume 24, page 895.<br /><br />Newton, before publilshing Principia, had not yet realized the cosmic applications of the laws of motion, as Britannica earlier notes:<br /><br />"What is more, Hooke's definition of orbital motion---in which the constant action of an attracting body continually pulls a body away from its inertial path---suggested a cosmic application for Newton's concept of force and an explanation of planetary paths employing it. In 1679 and 1680, Newton dealt only with orbital dynamics; he had not yet arrived at the concept of universal gravitation." - Ibid., p. 894.<br /><br />Note that Newton did eventually grasp that the laws of motion had cosmic applilcations.<br /><br />It seems, as the above quotes show, that Newton eventually realized that universal gravitation, or the lack thereof, would cause more or less attraction which would then effect the initertial path more or less - resulting in direction of motion, for example.<br /><br />Do you have some reason to disagree with this conclusion?

 

[igorsboss]

Of course everything is in motion, but all Newtonian motion is measured against a fixed coordinate system. During early expansion, space itself was being altered. The coordinate system itself was being altered and twisted in ways that Newton's physics is unable to model correctly. I'm not insulting Newton or his physics here; I'm merely pointing out that the Newtonian model has its limits, and one of those limits is expansion.<br /><br />Hence the answer to:<br /><br /><font color="yellow">...can you or someone put numbers to F=MA in the example of the acceleration of expansion of our universe?</font><br /><br />is No.<br /><br />The statement f=ma merely says that force and acceleration are directly related, and that inertial mass is the constant of proportionality.<br /><br />Universal expansion just doesn't work that way.

 

[newtonian]

igorsboss - OK, so motion on the spacetime fabric can be modeled by Newtonian math, but motion of the fabric, aka expansion, cannot be so modeled?<br /><br />I certainly agree, for example, that Einstein expanded on Newton's model - pun intended.<br /><br />You posted earlier:<br /><br /><br />I believe the expression f=dp/dt is valid in a wider range of conditions, particularly at high speeds. <br /><br />So, can you punch in numbers for f=dp/dt instead of F =MA?<br /><br />Or do you think some other equation is required?

 

[igorsboss]

<font color="yellow">OK, so motion on the spacetime fabric can be modeled by Newtonian math, but motion of the fabric, aka expansion, cannot be so modeled?</font><br /><br />Yes.<br /><br /><font color="yellow">can you punch in numbers for f=dp/dt instead of F =MA?</font><br /><br />That's too hard for my little brain. Punch in numbers for what, exactly?<br /><br /><font color="yellow">Or do you think some other equation is required?</font><br /><br />I think some other question is required. To that end, I ask you what you are tring to understand or learn by asking this question?<br /><br />It sounds to me like perhaps you're trying to figure out the sum total of all the energy in the universe, in whatever form it may be. (if so, I'll warn you now that this eventually leads to a dead end...)

 

[electronman]

It maybe a bit hard to conclude using F=MA to prove or arrive what the rate of expansion of the universe is, however one can use the doppler of a signal as a way to measure acceleration just like Hubble did who proved the expansion of the universe because of the the redshift(not to many blue shift) meaning the frequency of the signal we are getting from say a target galaxy appears stretching out or going down to a lower frequency from a stable reference source. After all in our understanding you know that acceleration just like doppler is a second degree deriviative the former in lineal or radian measure while the latter is in cycles or revolutions, if you will. My arguement may not be strong so I'm open to discussion.<br /><br />I came I saw I learn