Are g or kg ever a proper unit for weight? A = YES

[NoMoShocks]

I have been Goggling, and not found a definitive answer to this question.

Are grams or kilograms ever proper to use as units of weight. Most web results I have found clearly identify these as units of mass, but then there is also a plethora of conversion charts between Kg and pounds that imply they can be used for weight as well.

I realize there seems to be a common convention to use g. and Kg as units of weight here on Earth, but is it really proper if you start talking about weights of objects in other places in the universe?

Last night, my daughter in 8th grade asked me for some tutoring on a science worksheet titled Fundamentals of Earth Science, Mass, Weight and Gravity, Copyright © Glencoe/McGraw Hill.

Two of the questions bothered me:
6. On Earth, an astronaut weighs 60 Kg. How much will she weigh on the moon?
7. The gravity on Jupiter is 2 – ½ times that of Earth. How much would the 60 Kg astronaut weigh if she could land on Jupiter?

Knowing that Kg is an SI unit of Mass, and Newton is an SI unit of weight, I went to the narrative above these questions to look for a description of gravitational constants to review with my daughter. All that I found were these very general statements:

“The weight of an object is a measure of the amount of force with which gravity is pulling on an object.”

“The mass of an object is the same everywhere. But the weight changes if the force of gravity changes.”

There was not any quantitative explanation of the relationship between units of mass and weight or gravitational constants.

I can understand Glencoe/McGraw Hill wanting to start with simpler concepts, and I can understand them wanting to continue with reinforcing the SI system of units, but I cannot understand reinforcing incorrect concepts that will need to be unlearned later.

Although it may be a common convention here on Earth to refer to weights in Kg, as soon as they start bringing weight on the Moon and Jupiter into the questions, they need to introduce Newtons.

An alternative could have been to use pounds, since the gravitational constant on Earth is unity, and then it might have been legitimate to introduce separate units for pounds mass, pounds weight, Kg and Newtons in a later more advanced lesson.

I found it impossible to coach my daughter to enter the answers I believe they were expecting, that a 60 Kg astronaut would weigh 10 Kg on the moon because the force of gravity is 1/6 that of the earth and the astronaut would weigh 150 Kg on Jupiter because the gravity of Jupiter is 2.5 times that of the Earth..

I asked my daughter teacher about this and the response I got was this:
I think you are correct. Glencoe/McGraw Hill wants to start with simple concepts while introducing differences between mass and weight. The purpose of this worksheet is to distinguish between mass and weight and how gravity influences that. For now we are using grams and kilograms as a unit of mass and/or weight. Later this year we will also learn about Newtons as a unit of weight (and/or force). The metric system, and the concepts of mass, weight and gravity are difficult topics for most students. As science and math teachers we have found that kids digest complex information in short sequential steps. These concepts will be developed and built upon later in more advanced lessons.

I can understand taking baby steps, but I still am having problems accepting the idea of teaching something that is wrong as a stepping stone to teaching the correct concepts.

What does everyone else think? Should I get a life instead?

[NoMoShocks]

I have been Goggling, and not found a definitive answer to this question.

Are grams or kilograms ever proper to use as units of weight. Most web results I have found clearly identify these as units of mass, but then there is also a plethora of conversion charts between Kg and pounds that imply they can be used for weight as well.

I realize there seems to be a common convention to use g. and Kg as units of weight here on Earth, but is it really proper if you start talking about weights of objects in other places in the universe?

Last night, my daughter in 8th grade asked me for some tutoring on a science worksheet titled Fundamentals of Earth Science, Mass, Weight and Gravity, Copyright © Glencoe/McGraw Hill.

Two of the questions bothered me:
6. On Earth, an astronaut weighs 60 Kg. How much will she weigh on the moon?
7. The gravity on Jupiter is 2 – ½ times that of Earth. How much would the 60 Kg astronaut weigh if she could land on Jupiter?

Knowing that Kg is an SI unit of Mass, and Newton is an SI unit of weight, I went to the narrative above these questions to look for a description of gravitational constants to review with my daughter. All that I found were these very general statements:

“The weight of an object is a measure of the amount of force with which gravity is pulling on an object.”

“The mass of an object is the same everywhere. But the weight changes if the force of gravity changes.”

There was not any quantitative explanation of the relationship between units of mass and weight or gravitational constants.

I can understand Glencoe/McGraw Hill wanting to start with simpler concepts, and I can understand them wanting to continue with reinforcing the SI system of units, but I cannot understand reinforcing incorrect concepts that will need to be unlearned later.

Although it may be a common convention here on Earth to refer to weights in Kg, as soon as they start bringing weight on the Moon and Jupiter into the questions, they need to introduce Newtons.

An alternative could have been to use pounds, since the gravitational constant on Earth is unity, and then it might have been legitimate to introduce separate units for pounds mass, pounds weight, Kg and Newtons in a later more advanced lesson.

I found it impossible to coach my daughter to enter the answers I believe they were expecting, that a 60 Kg astronaut would weigh 10 Kg on the moon because the force of gravity is 1/6 that of the earth and the astronaut would weigh 150 Kg on Jupiter because the gravity of Jupiter is 2.5 times that of the Earth..

I asked my daughter teacher about this and the response I got was this:
I think you are correct. Glencoe/McGraw Hill wants to start with simple concepts while introducing differences between mass and weight. The purpose of this worksheet is to distinguish between mass and weight and how gravity influences that. For now we are using grams and kilograms as a unit of mass and/or weight. Later this year we will also learn about Newtons as a unit of weight (and/or force). The metric system, and the concepts of mass, weight and gravity are difficult topics for most students. As science and math teachers we have found that kids digest complex information in short sequential steps. These concepts will be developed and built upon later in more advanced lessons.

I can understand taking baby steps, but I still am having problems accepting the idea of teaching something that is wrong as a stepping stone to teaching the correct concepts.

What does everyone else think? Should I get a life instead?

[galaxee]

all my measures of "weight" are in mg or g at work. atomic weights are in g/mol so i calculate the number of g to add to my buffer solutions.

physics was never my strong suit...

[galaxee]

all my measures of "weight" are in mg or g at work. atomic weights are in g/mol so i calculate the number of g to add to my buffer solutions.

physics was never my strong suit...

[Godiva]

Yes. Grams and kilograms are proper units of weight.

weight conversion calculator.

[Godiva]

Yes. Grams and kilograms are proper units of weight.

weight conversion calculator.

[dogfriend]

W=mg.

Weight is the force of gravity so it is properly expressed in Newtons (N)

Kilograms is actually a unit of mass.

Kilogram-force is actually what people are using when they specify weight in Kilograms.

http://en.wikipedia.org/wiki/Weight

[dogfriend]

W=mg.

Weight is the force of gravity so it is properly expressed in Newtons (N)

Kilograms is actually a unit of mass.

Kilogram-force is actually what people are using when they specify weight in Kilograms.

http://en.wikipedia.org/wiki/Weight

[F8L]

While I do not see any problem with taking baby steps I think your real issue with the actual question posed to your child. The lesson plan could have used different scenarios to explain mass, density, volume etc. and not run the risk of being confusing to the child later on in their studies. On the otherhand, it may not be so harmful considering some principles apply only to specific scenarios. Think the macro world vs the subatomic world (classical physics vs quantum mechanics). Kinda. I'm not a physicist so please excuse my courseness.

So in essence, there are many cases where one may have to forget what they know about a particular subject and apply new principles when studying a different subject. For example. In biology we would define "Kinetic Energy" slightly different than a physicist would. We may define it as thermal energy as opposed to the energy of motion because it makes more sense when learning biology. Or we may define Potential Energy as stored energy or as chemical energy (bonds between molecules). So being able to develop flexibility with definitions depending on context is not a bad thing. Context is everything!

Yes, Kg is used to measure weight very often if one considers weight the same as mass in general terms. Pull up nearly living organism on the web and it will list it's weight (mass) in Kg or appropriate prefix added to gram. To be very specific you may have to use kilogram-force but I don't know much about this so here is what Wiki says. lol

Feel free to correct me in any of this. I'm still learning.

[F8L]

While I do not see any problem with taking baby steps I think your real issue with the actual question posed to your child. The lesson plan could have used different scenarios to explain mass, density, volume etc. and not run the risk of being confusing to the child later on in their studies. On the otherhand, it may not be so harmful considering some principles apply only to specific scenarios. Think the macro world vs the subatomic world (classical physics vs quantum mechanics). Kinda. I'm not a physicist so please excuse my courseness.

So in essence, there are many cases where one may have to forget what they know about a particular subject and apply new principles when studying a different subject. For example. In biology we would define "Kinetic Energy" slightly different than a physicist would. We may define it as thermal energy as opposed to the energy of motion because it makes more sense when learning biology. Or we may define Potential Energy as stored energy or as chemical energy (bonds between molecules). So being able to develop flexibility with definitions depending on context is not a bad thing. Context is everything!

Yes, Kg is used to measure weight very often if one considers weight the same as mass in general terms. Pull up nearly living organism on the web and it will list it's weight (mass) in Kg or appropriate prefix added to gram. To be very specific you may have to use kilogram-force but I don't know much about this so here is what Wiki says. lol

Feel free to correct me in any of this. I'm still learning.