Does a scale *display* weight or mass?

  • Context: High School 
  • Thread starter Thread starter AmagicalFishy
  • Start date Start date
  • Tags Tags
    Mass Scale Weight
Click For Summary
SUMMARY

Bathroom scales measure weight, which is a force, through the displacement of a spring. However, the numbers displayed on these scales are effectively the weight divided by the local gravitational acceleration (g), which is typically assumed to be 9.80665 m/s² on Earth. This means that while the scale shows a mass reading, it is actually a representation of weight adjusted for Earth's gravity. If used on the moon, the scale would yield incorrect values unless corrected for the lower gravitational force.

PREREQUISITES
  • Understanding of weight as a force and its measurement principles
  • Knowledge of gravitational acceleration (g) and its variations
  • Familiarity with the concept of mass versus weight
  • Basic physics principles related to scales and force measurement
NEXT STEPS
  • Research the differences between weight and mass in physics
  • Learn about gravitational acceleration variations on Earth and other celestial bodies
  • Explore advanced scale technologies that can measure and display mass directly
  • Investigate the principles behind force measurement using springs and displacement
USEFUL FOR

Physics students, engineers, and anyone interested in the principles of measurement and the functioning of scales in different gravitational environments.

AmagicalFishy
Messages
50
Reaction score
1
I know that scales measure weight (a force) via displacement of a spring. I also know the difference between a force and a mass. I know that, on the moon, the numbers on a scale might be different (depending on the answer to this question). I've read through the few threads on this matter here, and there isn't a clear answer to my question:

What are the numbers that a bathroom scale actually displays? Are the numbers displayed a force, or does the scale implicitly assume it is on Earth, account for this—and thus display a mass?

 
Physics news on Phys.org
There's been quite a few threads on this subject over the years
have a look down at the bottom of your thread page and you will see some of the similarly titled threads
have a look through and see if they answer your questions ... if there is still anything unclear
then ask specific questions :smile:

cheers
Dave
 
The scale measures force, that is weight. But instead of displaying force or weight, the numbers you see are weight divided by a factor, the downwards accelaration on the Earth's surface, so as to display mass.

If you used such a scale on the moon, the values would be incorrect, although you could easily make the correction by simply multiplying the correct factor.
 
AmagicalFishy said:
What are the numbers that a bathroom scale actually displays?
Is there no unit displayed or written on your scale?
 
AmagicalFishy said:
I know that scales measure weight (a force) via displacement of a spring. I also know the difference between a force and a mass. I know that, on the moon, the numbers on a scale might be different (depending on the answer to this question). I've read through the few threads on this matter here, and there isn't a clear answer to my question:

What are the numbers that a bathroom scale actually displays? Are the numbers displayed a force, or does the scale implicitly assume it is on Earth, account for this—and thus display a mass?

Most scales are calibrated for one value of g. So if you put a known mass on a scale it will read slightly differently at different places on the Earth (eg near a mountain where g is very slightly higher or on the moon where it's lower). That demonstrates they are measuring and displaying weight not mass.

If you wanted them to measure weight but display mass they would have to automatically correct for variations in g.

Edit; You could make one that measured and displayed mass - for example by counting atoms or perhaps by using a horizontal spring and vibrating the mass.
 
Last edited:
Scales assume a local g level of 9.80665 (m/s)/s, the result is mass (kg) and weight (kgf) provided your at the Earth's surface radius.
 

Similar threads

  • · Replies 35 ·
2
Replies
35
Views
4K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 22 ·
Replies
22
Views
873
  • · Replies 202 ·
7
Replies
202
Views
13K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 51 ·
2
Replies
51
Views
5K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 23 ·
Replies
23
Views
2K