Measuring Mass without Newton's Law: Possible?

In summary, the conversation discusses the possibility of measuring mass without using Newton's laws, specifically the example of using a balance scale. The use of a balance scale is considered an operational definition of mass, and while it does rely on the concept of gravity, it does not directly measure gravitational force. Other possible ways of measuring mass, such as through active gravitational mass or measuring gravitational redshift, are also mentioned. The conversation also touches on the idea of defining inertial mass and the limitations of excluding certain categories of measurement.
  • #1
ravikannaujiya
38
0
Hi! I have been searching for examples where mass can be measured without using Newton's law but I could not find one. Please explain, can we measure mass without using Newton's laws? How?
PS: please don't explain using mass energy equivalence.
 
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  • #2
Why do you believe that such an example might exist?
 
  • #3
because mass is a fundamental quantity so we must have a way to measure it irrespective of knowledge of force.
 
  • #5
If you attach a mass ##m_1## to a spring on a horizontal surface, stretch the spring by a certain amount, let go, measure the acceleration ##a_1##, then do the same for mass ##m_2##, it is an experimental fact that ##m_1 a_1 = m_2 a_2##.
You can therefore pick any arbitrary mass and measure other masses in terms of that mass using the procedure outlined above (this is called an operational definition).
In the case of the SI units, we express mass in terms of kilograms. What's a kilogram? Well, the kilogram is the hunk of metal kept in Sèvres, France.
 
  • #6
MohammedRady97 said:
(this is called an operational definition)

What makes you sure that this is a definition for mass?
 
  • #7
Balances use concept of gravitation force that's why pointer of a balance tilts towards the object with greater mass and it is not a universal instrument for the measurement of mass (as it doesn't work in space or in free fall). m1a1=m2a2. doesn't it smell like Newton's law. Let me reframe the question... can we measure mass of an object without changing its state of motion as the time we change the state of motion we get the idea of force?
 
  • #8
ravikannaujiya said:
Balances use concept of gravitation force that's why pointer of a balance tilts towards the object with greater mass and it is not a universal instrument for the measurement of mass (as it doesn't work in space or in free fall). m1a1=m2a2. doesn't it smell like Newton's law. Let me reframe the question... can we measure mass of an object without changing its state of motion as the time we change the state of motion we get the idea of force?
We could (in principle) measure its active gravitational mass: Hold it steady and see how strongly it attracts nearby objects.
 
  • #9
jbriggs444 said:
We could (in principle) measure its active gravitational mass: Hold it steady and see how strongly it attracts nearby objects.

How do you measure the attraction of nearby objects without using forces or changing their state of motion?

How about measuring the gravitational redshift or time dilation instead?
 
  • #10
DrStupid said:
How do you measure the attraction of nearby objects without using forces or changing their state of motion?
I was answering the reframed question which does not forbid us from having nearby objects move.
 
  • #11
jbriggs444 said:
I was answering the reframed question which does not forbid us from having nearby objects move.

ravikannaujiya didn't mentioned it in his rephrased question, but he also wrote

ravikannaujiya said:
m1a1=m2a2. doesn't it smell like Newton's law.

This applies to all objects.
 
  • #12
ravikannaujiya said:
Balances use concept of gravitation force that's why pointer of a balance tilts towards the object with greater mass and it is not a universal instrument for the measurement of mass (as it doesn't work in space or in free fall).
The actual gravitational force doesn't matter, as long as the field is uniform over the size of the balance. The same balance measurement will allow you to measure the mass on Earth, on the Moon, and on Jupiter despite the widely different gravitational forces involved. So a balance scale is not measuring gravitational force, it is in fact measuring mass. It does require a uniform gravitational field, but as long as the forces don't break the structure they are not important themselves.

ravikannaujiya said:
can we measure mass of an object without changing its state of motion as the time we change the state of motion we get the idea of force?
Again, yes, use a balance scale. A balance scale is the traditional method for measuring mass.
 
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  • #13
DrStupid said:
What makes you sure that this is a definition for mass?

I'm sure that's one way of defining inertial mass, according to Introduction to Mechanics by Kleppner and Kolenkow at least.
 
  • #14
Well,you have four choices:
Inertial Mass (which you have ruled out)
Active gravitational mass (very small so is hard to measure, though not impossible)
Passive gravitaional mass (already suggested)
Mass-energy (also you have ruled out)
I'm not sure where we go from here. Is there a fifth option?
 
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  • #15
I also think that this general approach is fairly pointless.

You can take any measurable quantity, and on personal whim decide to exclude different categories of measurement. If you keep indulging your whims then you will eventually exclude every possible measurement. You will then have a fiat "unmeasurable" quantity. So what?

In the end you learn more about your whims than about physics.
 
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  • #16
MohammedRady97 said:
I'm sure that's one way of defining inertial mass, according to Introduction to Mechanics by Kleppner and Kolenkow at least.

With Galilean transformation it would be way of defining inertial mass. But with Lorentz transformation it results in something different which is not even a scalar.
 
  • #17
DaleSpam said:
The actual gravitational force doesn't matter, as long as the field is uniform over the size of the balance. The same balance measurement will allow you to measure the mass on Earth, on the Moon, and on Jupiter despite the widely different gravitational forces involved. So a balance scale is not measuring gravitational force, it is in fact measuring mass. It does require a uniform gravitational field, but as long as the forces don't break the structure they are not important themselves.

Again, yes, use a balance scale. A balance scale is the traditional method for measuring mass.
First, if mass are different, force due to gravity is not same. Its only acceleration due to gravity is same, and that's why when we compare two masses in uniform gravitational field acceleration due to gravity cancels out from both side...so, here we have relative scale to measure mass using gravity without having the knowledge of acceleration due to gravity. When I said space I meant when object experiencing only force due to gravity, that is also the case of free fall. Balances experiences not only force due to gravity but also reaction/tension/normal (whichever kind of balance may be)from the ground (you can understand by free body diagram). So, you say, we can use balance to measure mass in free fall.
 
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  • #18
ravikannaujiya said:
so, here we have relative scale to measure mass using gravity
Yes. Wasn't that what you wanted?

ravikannaujiya said:
When I said space I meant when object experiencing only force due to gravity, that is also the case of free fall. Balances experiences not only force due to gravity but also reaction/tension/normal (whichever kind of balance may be)from the ground (you can understand by free body diagram). So, you say, we can use balance to measure mass in free fall.
:rolleyes: OK, I could have worded my post more precisely. I should have specified that the scale should be at rest in the uniform field. That doesn't change the point that this is a measurement of mass (passive gravitational mass specifically).
 
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  • #19
yes I want that but not on the expanse of changing the state of motion and it only works in presence of gravity. However, thank you very much guys for replying, I think I got my answer.
We cannot measure mass in Newton's laws without changing the state of motion of an object. and its almost given in the definition itself. as the reasoning goes:
Mass is a measurement of inertia.
Inertia is a tendency to resist a change in state of motion of an object.
So, if there is no change in state of motion, we would not observe any tendency to resist its state of motion.
so, we don't measure inertia (mass).
 
  • #20
ravikannaujiya said:
We cannot measure mass in Newton's laws without changing the state of motion of an object.
Sure we can. I gave you an example of a standard way to measure mass where the object is at rest and remains at rest so the state of motion is unchanged. You may choose to ignore that example on a whim, but that is your whim and not physics.

ravikannaujiya said:
Mass is a measurement of inertia.
That is not all mass is, as was pointed out above by Jilang. Mass is also the source of gravitation, the thing affected by gravitation, and a measure of the energy of an object at rest.

Obviously, you cannot measure the a in F=ma without changing the state of motion, but you can measure the m. Not that this fact has any importance.
 
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  • #21
ohk.. thanks.
 
  • #22
officialmanojsh said:
Mass is nothing but calculation of amount of matter present in a body.

What do you mean with "amount of matter"?
 

1. How is mass measured without using Newton's Law?

Mass can be measured using a balance scale or a mass balance. These devices use the principle of conservation of mass, which states that the mass of an object remains constant regardless of its position or orientation. By comparing the mass of an unknown object to the mass of known objects, the mass of the unknown object can be determined without using Newton's Law.

2. Is it accurate to measure mass without using Newton's Law?

Yes, it is possible to measure mass accurately without using Newton's Law. The principle of conservation of mass has been extensively tested and has been found to hold true in all cases. As long as the balance scale or mass balance is calibrated properly, the mass measurement will be accurate.

3. Are there any limitations to measuring mass without Newton's Law?

There are some limitations to measuring mass without Newton's Law. This method relies on the assumption that the principle of conservation of mass holds true, which may not be the case in extreme conditions such as near the speed of light. Additionally, this method may not be suitable for very small or very large objects, as the balance scale may not be sensitive enough to accurately measure their mass.

4. Can mass be measured without using Newton's Law in space?

Yes, mass can be measured without using Newton's Law in space. In fact, this method may be more suitable for measuring mass in space as there is no gravitational force acting on the objects being measured. This eliminates any potential discrepancies caused by gravitational forces and allows for more accurate mass measurements.

5. What are the advantages of measuring mass without Newton's Law?

There are several advantages to measuring mass without using Newton's Law. This method is not affected by external factors such as gravitational forces, making it more accurate in certain situations. It also does not require specialized equipment, making it more accessible and cost-effective. Additionally, this method can be used to measure the mass of objects in space, where Newton's Law may not apply.

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