/sci/ - Science & Math

[Anonymous No.3827192]

Why is it that when we weigh something on a scale, the scale gives us a mass unit like kilograms. Why don't scales give readings in force units, ergo Newtons.

I thought I understood Newtonian physics until I realized this.

Obviously the scales are reading a force, or are the scales automatically dividing by the gravitational acceleration to give a mass?

If I calculate something's mass based on moles and atomic masses and then put it on a scale, will I get the mass that I calculated or will I get the mass multiplied by 9.8? I'm a chem major so I know the answer to this question already, but it just seems so bizarre for all scales to divide by 9.8 instead of giving a reading based on what it is actually measuring.

I'm not satisfied though, I feel like there's probably more going on here with how scales work. Anyone?

[Anonymous No.3827229]

>>3827192
> are the scales automatically dividing by the gravitational acceleration to give a mass?

Yes. Mass is more useful and general than weight-scales just use a useful ever-present force (gravity) and convert it to the more useful quantity.

[Anonymous No.3827240]

You are perhaps confusing a balance and a scale. A balance does just what it suggests. It compares an unknown mass to a known mass by balancing them. The effect of gravity cancels out so you can measure mass.

A scale measures the force a mass exerts under the influence of gravitational acceleration. A scale can still read a mass if you assume the acceleration due to gravity is constant everywhere on the planet. This turns out to be a reasonably accurate assumption for practical purposes. So a scale does measure force. But, if you assume acceleration due to gravity is a constant for all users of the scale then just divide it out to get the mass.

It might also help you to know in english units there are two types of pounds. Pounds(lb) are a unit of mass and a pound force(lbf) is a unit of force calibrated to 1 pound of mass under the influence of 1g of acceleration. So in practice they would have the same value for everyday common measurements. As soon as non gravitational forces are introduced this equivalence rapidly breaks down.

The SI system resolves this confusion by having a unit of mass called grams and a unit of force called newtons.

[Anonymous No.3827262]

Protip: scales that aren't retarded give a unit of force.

For example, a pound is actually a unit of force, like Newtons.

If your scale is giving you a unit of mass, they're lying.

[Josef crossed the Atlantic !!nUf2NflSAyw No.3827288]

>>3827262
That's wrong. A scale measures mass, since the gravitational field strength used to build it is constant enough around the world that it doesn't influence the measurement. High-precision scales used in chemistry labs have to be gauged every now and then though.
If you're arguing that that's just an assumption - then so is constant spring constant (or piezo or whatever the scale is using). You'd then have to say that scales measure distance, not force or mass.

[Anonymous No.3827624]

> Obviously the scales are reading a force, or are the scales automatically dividing by the gravitational acceleration to give a mass?
Scales you'll buy in a store were designed for use on Earth. They just divide the measured force by 9.81 m/s^2 to give kg. If you try to use them on the moon or Mars, they'll underestimate the mass significantly. If you try to use them on Jupiter, you'll be dead so it won't really matter.

[Anonymous No.3827663]

Random thought. How the fuck do scales work?