Weight & Mass

stickyfiddle

I've spent half the day arguing on a facebook page about weight and mass and how to measure them, so thought I'd put the same question up here. 

Someone had homework with the following question. How would you reply and why?

Jack wanted to know the weight of an object. What instrument should he use?

a) scale

b) rule

c) lightmeter

d) forcemeter

CabbageCat

I think I'd probably use a scale. Because it weighs things.

hobbio

Assuming he's doing it on Earth, I'd say a scale too.

lloyd

A scale.

CabbageCat

hobbio said:

Assuming he's doing it on Earth, I'd say a scale too.

If he's doing in on Tattoine I'd probably still use a scale but I might use a forcemeter if there were valid suspicions of a high midichlorian count. 

Phil_aka_Pip

Who's Jack?

Philly_Q

Isn't the difference that mass is fixed but weight depends on gravity?

The weight is the force experienced due to gravity, so the answer may be forcemeter.... if, indeed, there is such a thing as a forcemeter.

In the real world I'm sure Jack would use a scale, since he's not likely to be going anywhere where gravity is different.

quarky

D. No, A. Maybe. Whichever one has newtons on it.

stickyfiddle

Phil_aka_Pip said:

Who's Jack?

It was "Suleman" in the original question, but I thought I'd anglicise it

 

not_the_dj

Weight is a force...so forcemeter.

Or a scale to get the mass and multiply by gravitational acceleration (g)

crunchman

It's not a good question.

Strictly speaking weight is a Force so you could measure it with a forcemeter.  Having said that you would normally get it by using scales and multiplying the mass you read in kg by 9.81 m/s2.

If you want to get pedantic about it though, what you read as mass on a set of scales calibrated in kg is would only be correct at sea level on earth (or somewhere else where the acceleration due to gravity is 9.81m/s2).  Given the principles that most scales work on they actually measure weight not mass even if the units on them are kg.   If you had something that showed as 6kg on a set of scales on earth then they would incorrectly show as 1kg on the moon even though the object has a mass of 6kg.  They should really show weight in Newtons.

PC_Dave

e) Google.

stickyfiddle

Philly_Q said:

Isn't the difference that mass is fixed but weight depends on gravity?

The weight is the force experienced due to gravity, so the answer may be forcemeter.... if, indeed, there is such a thing as a forcemeter.

In the real world I'm sure Jack would use a scale, since he's not likely to be going anywhere where gravity is different.

That's what the teacher said, apparently. Loads of people have been arguing that scale is wrong because it doesn't read out in Newtons, but that's really completely irrelevant as a basic scale (ie one with a single plate and a spring mechanism) IS a type of forcemeter, used to measure the force between the earth and the object sitting on the scale. 

I can totally see that a see-saw-type weight balance might not be the right answer, but ultimately it's a crappy question.

PC_Dave

Major Scale? Or Minor Scale?

Col_Decker

What are those things in the bathroom for measuring your weight called again? Oh yes Bathroom Force-meters.

lloyd

It's a fucking stupid question, every time I've needed to know what something weighs, I weigh it, on a scale because that tells me what it weighs.

I hope all my drug dealers do too, I want an earth gramme of cocaine, not a jupiter one.....Or is that the other way round, I'm no scientist.

maltingsaudio

Isn't force weight times acceleration?

martinw

maltingsaudio said:

Isn't force weight times acceleration?

No. Mass x Acceleration.

Weight is a force!

maltingsaudio

martinw said:

maltingsaudio said:

Isn't force weight times acceleration?

No. Mass x Acceleration.

Weight is a force!

Brain hurts

Sesh

stickyfiddle said:

Philly_Q said:

Isn't the difference that mass is fixed but weight depends on gravity?

The weight is the force experienced due to gravity, so the answer may be forcemeter.... if, indeed, there is such a thing as a forcemeter.

In the real world I'm sure Jack would use a scale, since he's not likely to be going anywhere where gravity is different.

That's what the teacher said, apparently. Loads of people have been arguing that scale is wrong because it doesn't read out in Newtons, but that's really completely irrelevant as a basic scale (ie one with a single plate and a spring mechanism) IS a type of forcemeter, used to measure the force between the earth and the object sitting on the scale. 

I can totally see that a see-saw-type weight balance might not be the right answer, but ultimately it's a crappy question.

It is a crappy question. It is hard to gauge what scientific level this is aimed at. If it is for an 8 year old then scale would be correct enough in my opinion. A "weighing scale" should really be called a "balance."

I don't see what a question has to gain by being a smartarse.

stickyfiddle

Sesh said:

stickyfiddle said:

Philly_Q said:

Isn't the difference that mass is fixed but weight depends on gravity?

The weight is the force experienced due to gravity, so the answer may be forcemeter.... if, indeed, there is such a thing as a forcemeter.

In the real world I'm sure Jack would use a scale, since he's not likely to be going anywhere where gravity is different.

That's what the teacher said, apparently. Loads of people have been arguing that scale is wrong because it doesn't read out in Newtons, but that's really completely irrelevant as a basic scale (ie one with a single plate and a spring mechanism) IS a type of forcemeter, used to measure the force between the earth and the object sitting on the scale. 

I can totally see that a see-saw-type weight balance might not be the right answer, but ultimately it's a crappy question.

It is a crappy question. It is hard to gauge what scientific level this is aimed at. If it is for an 8 year old then scale would be correct enough in my opinion. A "weighing scale" should really be called a "balance."

I don't see what a question has to gain by being a smartarse.

It's for 6th grade, apparently, which is 11-12 year olds. 

I completely get what the teacher is trying to achieve, but it's badly worded and misleading. I now have a bunch of teachers on facebook telling me it's not misleading or badly worded. They're wrong.