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Attacking Einstein (and other pursuits) 
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#1
Jan2410, 10:37 PM

P: 16

Hello...
I have heard that the speed of light is 300,000km/s. Planks constant is another number and so on and so on and so on. Alot of these numbers seem to be very 'arbitrary' figures.... Is there a subject in physics called "parameter" analysis where the various arbitrary numbers and constants in physics are studied to give some understanding or reason for their magnitude? Also, is there another area in physics that provides principled or theoretical or a logical foundation for the various terms in physics like ...m/s, kg/m/s etc.etc.etc. that were introduced in physics to formulate various theory's. Sorry.. a bit of a vague question. * In the equation P=mv (which is the equation for momentum)...if I switch the variables around I get M=P/v....Does this equation mean that if there is a change in momentum there is a "direct  and exactly porportional change in velocity? Eg. If P= 5m/s v will equal 5m/s? Thank you for any and all answers. Bye G. 


#2
Jan2410, 10:42 PM

Sci Advisor
PF Gold
P: 1,765

The constants are not arbitrary, our units of measurement are the arbitrary units. You can set the speed of light to whatever you want, ~3.0e8 m/s or 1 something/something. But this reflects a change in your system of units.
The change in momentum is equal to force via Newton's laws. Force is the product of mass and acceleration, the latter describing the change in velocity over time. 


#3
Jan2410, 11:05 PM

P: 4,663

The fundamental constants are overdetermined by many overlapping partially correlated precision measurements. A detailed discussion of the latest comprehensive leastsquares fit can be found at
http://physics.nist.gov/cuu/Constant..._000633acc.pdf A summary of the fundamental constant values can be found on pg 85 of the pdf. Bob S 


#4
Jan2510, 05:58 AM

P: 568

Attacking Einstein (and other pursuits)
For example, if an object has a velocity of 9 m/s and a momentum of 100 kg m/s, then for the same object, its mass unchanged, if its new velocity were 27 m/s, then its new momentum would be 300 kg m/s. This isn't a question about physics but a question about how to use fractions. In general, to say that A/B = some constant means that it's equally true to write that 3A / 3B is the same constant, or 94A / 94B = the same constant. 


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