# Weight- mass

#### Monika Verma

Joined Jan 23, 2016
14
Hello, I have a question.

We use spring balance to measure its weight. But the unit of weight is newton. That's why the units are written is gram/ kilogram. But they are unit of mass. Then what we really measure by spring balance.

#### Papabravo

Joined Feb 24, 2006
20,142
On the surface of the earth the unit of weight and the unit of mass are proportional to each other. That is why in common usage one can be substituted for the other. In the English system, the unit of mass is the slug and the unit of weight is the pound. Common usage is the pound. If you asked for 1/32 of a slug of sugar the shopkeeper would look at you as if you had a second head.

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
I'm a teacher of maths science. How can I explain it to my students?

#### Alec_t

Joined Sep 17, 2013
13,437
The spring balance measures the force exerted on a mass by Earth's gravity.

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
Then why its measured in gram and kilogram. Its have to measured in newton

#### Papabravo

Joined Feb 24, 2006
20,142
You explain to the students that Newton's Second Law provides the link between weight and mass.

F(newtons) = mass(kilograms) x acceleration(meters/sec/sec)

The acceleration in the above expression is the result of the earth exerting a force on an object and the object exerting a force on the earth. This number is 9.8 meters/sec/sec or 32.4 ft/sec/sec. This constant of proportionality means that newtons and kilograms can both be used to define how much of something you have. Similarly pounds and slugs can also be used to indicate the amount of something.

Also: An object will have mass regardless of where in the universe it is. The same object will have weight only in a gravitational field. The weight will be different on different planets, but the mass will remain the same.

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
Thank you for your response. I got my answer. I will try to explain them. But problem is that they don't study newton's law. It comes in std 9th syllabus. & the students are of 7th. And in gujarat the syllabus level is so poor. But I'll try my best. Thank u sir.

#### Papabravo

Joined Feb 24, 2006
20,142
Just stick with "mass is the same everywhere in the universe" and weight is only measurable in a gravitational field on the surface of a planet. You can mention that the two things are proportional to each other. That is they are related by a constant that you use to multiply by one to get the other. That is multiply mass by a constant to get weight(force).

• Monika Verma

#### hp1729

Joined Nov 23, 2015
2,304
So mass is a matter of atomic structure and weight is the result of that atomic structure in a gravity field?

• Monika Verma

#### Alec_t

Joined Sep 17, 2013
13,437
You can tell the students that an astronaut in zero-gravity on the International Space Station is weightless, but he has the same body mass there as he does on Earth.

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
Wow, great answer. Thank u so much to all of you for your help .

• GopherT

#### Papabravo

Joined Feb 24, 2006
20,142
So mass is a matter of atomic structure and weight is the result of that atomic structure in a gravity field?
Mass is a fundamental property of matter and anti-matter as well. No structure is required since it applies to elementary particles like quarks and leptons.

#### Monika Verma

Joined Jan 23, 2016
14
There are some rays from atom which depends the forces

#### joeyd999

Joined Jun 6, 2011
4,818
Thank you for your response. I got my answer. I will try to explain them. But problem is that they don't study newton's law. It comes in std 9th syllabus. & the students are of 7th. And in gujarat the syllabus level is so poor. But I'll try my best. Thank u sir.
I was told by a science teacher, in my early years, this:

"If you want to lose weight, go to the moon."

That helped.

Edit: and then you can elaborate: since the moon has 1/6 the gravity of earth, you will weigh 1/6th as much on the moon as you do on earth. Your mass, on the other hand, stays the same.

#### joeyd999

Joined Jun 6, 2011
4,818
I'm a teacher of maths science. How can I explain it to my students?
I have a question, and I don't mean to be offensive -- please don't take it as such.

If you are a "maths science" teacher, how is it that you don't know what is being measured on a spring balance? What are the requirements for being a "maths science" teacher in your locale?

Rationale for my question: if you don't know the answer, how are you qualified to impart such information to your students?

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
I know. But I can't explain it. Because students are from urbaan area. They also don't know what is circuit. I have to explain all thing. and there are no sufficient lectures . So how can I easily explain them? That's y I ask you. Students are so poor that they can't identify the difference between b and d. Its means they don't know ABCD as good.

#### hp1729

Joined Nov 23, 2015
2,304
There are some rays from atom which depends the forces
I can't think of any that don't, but that highlights my confusion.

#### WBahn

Joined Mar 31, 2012
28,484
Hello, I have a question.

We use spring balance to measure its weight. But the unit of weight is newton. That's why the units are written is gram/ kilogram. But they are unit of mass. Then what we really measure by spring balance.
As you explain to them the difference between weight and mass, tell them that because we all live in a place that has the same gravity everywhere (no need to get into the fine points on that just yet) the two might as well be the same for most purposes, and that as a result we tend to treat them as if they are the same in everyday life. Using the moon is good because most people know that there they would weigh 1/6th of what they do here. So to distinguish the two ask them the some questions where the distinction is important. For instance, let's say that they wanted to bake a large batch of something and the recipe called for six pounds of flour (and let's say that flour comes in six pound bags). If they went to the moon and wanted to bake the same thing what would be important -- not how much force the floor exerted on the table, but rather how much flour (how many molecules of flour, if you will) is used. So they would still use one six-pound bag of flour, regardless what it weighs. But now imagine that they were gluing some wood project together and to get the parts to set correctly they needed to put a six pound bag of floor on top of it overnight. If they were to do that same project on the moon, they would want the same force pressing down on the parts and so they would need to use six six-pound bags.

Here on Earth, we tend to use the terms 'mass' and 'weight' interchangeably and we also tend to use the units of mass and the units of force interchangeably -- and it doesn't matter if you use the English system or the metric system. In the English system we use the unit "pound" for both (the 'slug' is a contrived unit that is almost never used outside physics courses), which causes problems and is why, when it matters, we often distinguish them by using "pound-mass" and "pound-force". But in the metric system the "kilogram" is often used as a unit of force when "newton" is what should be used. It is very common, for instance, to see pressure gauges marked in kg/m².

• Monika Verma

#### Monika Verma

Joined Jan 23, 2016
14
Ya. I already explain about moon. They all are shocked. They all enjoy my lecture everyday and do all experiment as possible as I can did them . This project is good idea. I will surely say abou this. I've also exoplained its also happens on earth. Earth is not completely sphere. On north pole and on south pole the weight of matter change from here.

#### Glenn Holland

Joined Dec 26, 2014
703
I'm a teacher of maths science. How can I explain it to my students?
Trying to directly measure mass is not easily done. S

So the mass can be determined by measuring its weight where the acceleration of gravity is known. Another common method is to compare an unknown mass with a known one using a balance instead of a spring. Since the acceleration of gravity is the same for each mass, the difference reveals the unknown.

• Monika Verma