Calculating Mass Without Gravitational Force

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Discussion Overview

The discussion revolves around the concept of measuring mass without relying on gravitational force. Participants explore various methods and theories related to mass measurement, including the implications of gravitational variations at different heights and locations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that gravitational force varies with height and questions if mass can be measured without it.
  • Another suggests defining mass using the stress-energy tensor as an invariant method.
  • It is proposed that mass can be calculated using the relationship m = F/g, or by using m = F/a with a defined force and acceleration.
  • A participant mentions measuring mass through inertia or using a force balance.
  • Discussion includes the mass-spring system, where the period of oscillation is independent of gravitational force, allowing mass measurement based on oscillation time.
  • Clarifications are sought regarding the spring constant (k) and its role in the mass-spring system.
  • Another method discussed involves using a two-pan balance scale with calibrated masses, which is effective regardless of height.
  • Participants discuss the implications of measuring mass in a weightless environment, questioning the forces involved in such scenarios.

Areas of Agreement / Disagreement

Participants express multiple competing views on the methods of measuring mass and the role of gravity, with no consensus reached on a singular approach or definition.

Contextual Notes

Some methods discussed depend on specific conditions, such as the presence of a gravitational field or the characteristics of the measuring instruments. The discussion also highlights the potential for confusion regarding the distinction between mass and weight.

Who May Find This Useful

This discussion may be of interest to those studying physics, particularly in areas related to mechanics, measurement techniques, and the effects of gravity on mass.

Infinite/Zero
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We all can measure the mass of a body by any common instrument like Spring Balance.
But if we go from one place to another place the gravitational force will change,
like if we go from 1st floor to 10th floor or from coastal region to plateau region.
The gravitational force depend on the height.
Is there any way to calculate mass of a body without gravitational force ?
Please tell me if i am wrong, i will be thankful to you.
If i am not wrong than please answer me.
 
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The only 'invariant' way to define mass is using the stress energy tensor.
 
Using gravitation, m=F/g.

Use m = F/a, whereby if one can set up a system to determine the force F and the acceleration a, then surely the mass m can be calculated.
 
You can measure mass by means of its inertia, or with a force balance.
 
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Thank you all o:)
 
Can you please explain me "stress energy tensor" .
 
Actually, you may still use the mass-spring system to measure the mass if you simply measure the period of oscillation, which depends only on the ratio of k/m. Moving to a place with different g only changes the equilibrium position, not the period.

Zz.
 
What do you mean by k/m ?
please tell me.
 
Infinite/Zero said:
What do you mean by k/m ?
please tell me.

The strength of a spring is described by a quantity called its "spring constant", traditionally written as ##k##. If an object is hanging from a spring and you start it oscillating, the time for each oscillation will be ##\sqrt{k/m}## where ##k## is the spring constant and ##m## is the mass (not the weight!) of the object.

Thus, we can find the mass by hanging the object from a spring of known strength and measuring the time for one oscillation.
 
  • #10
Thanks Nugatory for responding my question.
Can your method of measuring mass of a body will give a constant mass at different height from Earth ?
Is it related to gravity ?
 
  • #11
Infinite/Zero said:
Thanks Nugatory for responding my question.
Can your method of measuring mass of a body will give a constant mass at different height from Earth ?
Is it related to gravity ?

It will give the same mass reading at all heights, and even if you are weightless in outer space.

It's actually a specific example of the general approach that 256bits suggested back in #2 of this thread: "Use m = F/a, whereby if one can set up a system to determine the force F and the acceleration a, then surely the mass m can be calculated."
 
  • #12
Nugatory said:
and even if you are weightless in outer space.
Which force will oscillate the body hanging on a spring in outer space ?

The second method m=F/a is good. Thanks :cool:
 
  • #13
Another way to do it is to use a two-pan balance scale that doesn't involve a spring. Here you use calibrated masses on one side of the scale to balance your unknown mass on the other side of the scale. This works on the top of a mountain, or at sea level. This is how we used to do it in chemistry lab back in the day.

Chet
 
  • #14
Infinite/Zero said:
Which force will oscillate the body hanging on a spring in outer space ?

The restoring force of the spring!

You might want to look at the mass-spring system and study its kinematics.

http://hyperphysics.phy-astr.gsu.edu/hbase/shm2.html

Zz.
 
  • #15
Thanks Zapperz:zzz:
 
  • #16
Infinite/Zero said:
Thanks Nugatory for responding my question.
Can your method of measuring mass of a body will give a constant mass at different height from Earth ?
Is it related to gravity ?

At Christmas time in the space station, when the Astronauts (Cosmonauts?) give each other presents wrapped up in boxes, they can get a clue about what's inside. They can shake the presents to get an idea of their mass (is it a cuddly toy or a bottle of Vodka?), even though the presents will both float in front of them. They are unconsciously using the equation F = ma to estimate the value of mass: more mass is harder to shake.
 

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