What does the scale reading represent?

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Discussion Overview

The discussion revolves around the interpretation of scale readings, specifically whether they represent weight or mass. Participants explore this concept in the context of different types of scales and the influence of gravitational fields.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about whether a scale reading indicates weight (w = mg) or mass (m), referencing their physics teacher's assertion that it measures mass.
  • Another participant notes that the type of scale matters; a bathroom scale measures the force exerted on it, which can represent either weight or mass depending on the context, such as location (e.g., on the moon).
  • A third participant explains that most weighing machines measure force due to mass in a gravitational field, while balances compare weight forces to eliminate variations in gravitational acceleration (g).
  • One participant suggests that mass can be measured without a gravitational field using an oscillating system of springs and known masses, highlighting the need for precise measurements of other variables.
  • Another participant states that scales measure weight due to gravitational influence and suggests dividing by 9.81 to find mass.
  • A final contribution questions whether the scale uses a balance beam and counterweight, indicating that such a scale measures mass, while others likely measure weight as a force.

Areas of Agreement / Disagreement

Participants present multiple competing views regarding whether scales measure weight or mass, and the discussion remains unresolved with no consensus reached.

Contextual Notes

Participants highlight the dependence on the type of scale and the gravitational context, indicating that assumptions about the environment and scale design affect the interpretation of readings.

jayadds
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Say that an object is placed on a scale and it gives a reading. Does that number represent the object's weight (w = mg) or mass (just m)? I'm a bit confused because my physics teacher told me that it is measuring its mass...is this correct?

Many thanks.
 
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Depends what kind of scale it is. If it's a scale like a bathroom scale, it essentially gives you a measure of the force pressing against it. The reading itself could be a weight or a mass, since they are proportional. But use that scale on the surface of the moon and it will read less, since your weight would be less there. But your mass hasn't changed.
 
Most 'weighing machines' measure a force - due to a mass in the presence of a gravitational field. If you use a balance (see-saw) you are comparing the weight forces of two masses so you can eliminate any variation of g. If you use a spring balance, you are just measuring the weight force in the presence of an uncertain value of g.

However, you can measure the mass of an object in the absence of any g field or a table to place it on if you include the object in an oscillating arrangement of springs and known masses. The mass of the object can then be found by measuring the frequency of oscillation of the system. Of course, this would involve knowing the values of the other masses and the exact stiffnesses of the springs - but the method would work anywhere.
 
The scales measure the objects weight, because when you place the object on the scales it is influenced by the gravitational pull. Weight=mg therefore to get the mass, you must divide 9.81
Thanks
Z.C
 
Does the scale have a balance beam and a counterweight? Then it measures mass. If it doesn't, then it probably measures weight, which is a force.
 

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