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So, will F=ma work if mass is in pounds mass and acceleration in ft/s^2, or will a proportionality constant need to be introduced to the equation? The same question applies to most if not all physics equations
What about gauss, statcoulombs, etc., the units of the cgs system?SteamKing said:Some physical properties have only SI definitions (like volts, amps, coulombs, and such where there are no non-SI units of measurement).
Of course. Newton's second law says force is proportional to rather than equal to the product of mass and acceleration. Newton viewed force as some distinct quantity and his second law as a law of nature.Woopydalan said:So, will F=ma work if mass is in pounds mass and acceleration in ft/s^2, or will a proportionality constant need to be introduced to the equation? The same question applies to most if not all physics equations
lugita15 said:What about gauss, statcoulombs, etc., the units of the cgs system?
On a side note: that c is not unitless in the SI, simply means that according to the SI length is physically different from time. [added:] However, indeed c and G could have been given the value 1.D H said:[..] That c is not 1 *and unitless* means that the International System is an inconsistent set of units. The same goes for F=GMm/r2. A consistent set of units has G=1, and once again, unitless.
Khashishi said:Most equations work no matter what units you use. However, many electromagnetic equations change depending on what units are used.
In your case, you can use F=ma to get the force in units of pounds[mass]*ft/s^2. One problem with imperial units is that force is usually measured in pounds[force], and you need a conversion constant to go from pounds[mass]*ft/s^2 to pounds[force] since they are totally different.
messysmurf said:Yes, of course it works, this is like asking does mathematics work in another base system, of course it does.
I don't see how SI units are inconsistent. It's not like you're required to set c=G=1. Planck units are just a convention that physicists find convenient to work with. You won't get a contradiction if you work in SI units.D H said:However, from this perspective, SI units are not consistent either. We have to write E=mc2 (better: E2=(mc2)2+(pc)2). If SI truly was a consistent set of units we would write that as E2=m2+p2. That c is not 1 *and unitless* means that the International System is an inconsistent set of units. The same goes for F=GMm/r2. A consistent set of units has G=1, and once again, unitless.
harrylin said:Force is a measure of mass and acceleration according to classical physics, and mass is a measure of energy content according to relativity. Also, for centuries weight was used as a measure of mass (and bathroom scales still use that). Proportional doesn't mean identical.
You won't get a contradiction in any set of units, that isn't what consistency is about.lugita15 said:You won't get a contradiction if you work in SI units.
I agree, I only hinted at that because I already mentioned another issue with a side topic.stevendaryl said:I don't think it's quite fair to view Newton's "F = ma" as a definition. [..] you can develop an entire science of "static" forces without ever thinking to connecting it to acceleration. [..]
DaleSpam said:You won't get a contradiction in any set of units, that isn't what consistency is about.
That isn't how it's used in the context of determining whether a set of units is consistent. The issue here is whether the system of units is consistent with modern physics. F=kma is not while F=ma is.stevendaryl said:Many people use the word "consistent" to mean "free of contradiction". That's certainly how it's used in mathematics.
Agreed. It is a "recycled" word where they probably should have come up with a new one. Same with the "dimensionality" of a unit.stevendaryl said:Many people use the word "consistent" to mean "free of contradiction". That's certainly how it's used in mathematics.
Why can't you use F=ma in English units, with mass measured in slugs, force measured in pounds, and acceleration measured in ft/s^2?D H said:The issue here is whether the system of units is consistent with modern physics. F=kma is not while F=ma is.
Nothing is stopping you from doing that.lugita15 said:Why can't you use F=ma in English units, with mass measured in slugs, force measured in pounds, and acceleration measured in ft/s^2?
In a parallel thread ghwellsjr makes use of nanoseconds and (very big) feet to make c=1 ft/nslugita15 said:Why can't you use F=ma in English units, with mass measured in slugs, force measured in pounds, and acceleration measured in ft/s^2?
That's an old joke from computer pioneer Grace Hopper.harrylin said:In a parallel thread ghwellsjr makes use of nanoseconds and (very big) feet to make c=1 ft/ns
Yes, physics equations can be used in non-SI units as long as the units used are consistent throughout the equation.
Some common non-SI units used in physics include imperial units such as feet, pounds, and seconds, as well as natural units such as Planck units and atomic units.
No, as long as the units are consistent, the accuracy of the calculations will not be affected by using non-SI units.
Yes, using non-SI units can sometimes make calculations easier and more intuitive, particularly in certain fields of physics such as astrophysics and quantum mechanics.
To convert non-SI units to SI units, you can use conversion factors or online conversion tools. It is important to double check your conversions to ensure accuracy in your calculations.