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

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.â€

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

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?

 

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.â€

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

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?

 

<div class='quotetop'>QUOTE(dogfriend @ Sep 12 2007, 08:37 PM) [snapback]511720[/snapback]</div>

Thanks Dogfriend. Your Wikipeda reference answered my question. There really is a unit of measure called the Kilogram-force, which although it it not an official SI unit, is in wide use on Earth and often abbreviated to just Kg. with "force" implied same as in pound-force. Hence, the existance of the conversion tables that I found and Godiva refered to.

So then, getting back to the questions that were bothering me, you could say that an astronaut who weighed 60 Kilograms-force on Earth would weigh 10 Kilograms-force on the moon, whith the understanding that the non-SI unit Kilograms-force is defined as the force exerted by 1 Kg-mass under the influence of the standard Earth gravity (1 kilogram-force = 9.81 Newtons)

Kilogram-force
From Wikipedia, the free encyclopedia
• Ten things you didn't know about images on Wikipedia •Jump to: navigation, search
The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. Although the gravitational pull of the Earth varies as a function of position on earth, it is here defined as exactly 9.80665 m/s². So one kilogram-force is by definition equal to 9.80665 newtons.[1]

The kilogram-force has never been a part of the International System of Units (SI), which was introduced in 1960. The SI unit of force is the newton.

Prior to this, the unit was widely used in much of the world; it is still in use for some purposes. The thrust of a rocket engine, for example, was measured in kilograms-force in 1940s Germany, in the Soviet Union (where it remained the primary unit for thrust in the Russian space program until at least the late 1980s), and it is still used today in China and sometimes by the European Space Agency.

 

<div class='quotetop'>QUOTE(dogfriend @ Sep 12 2007, 08:37 PM) [snapback]511720[/snapback]</div>

Thanks Dogfriend. Your Wikipeda reference answered my question. There really is a unit of measure called the Kilogram-force, which although it it not an official SI unit, is in wide use on Earth and often abbreviated to just Kg. with "force" implied same as in pound-force. Hence, the existance of the conversion tables that I found and Godiva refered to.

So then, getting back to the questions that were bothering me, you could say that an astronaut who weighed 60 Kilograms-force on Earth would weigh 10 Kilograms-force on the moon, whith the understanding that the non-SI unit Kilograms-force is defined as the force exerted by 1 Kg-mass under the influence of the standard Earth gravity (1 kilogram-force = 9.81 Newtons)

Kilogram-force
From Wikipedia, the free encyclopedia
• Ten things you didn't know about images on Wikipedia •Jump to: navigation, search
The unit kilogram-force (kgf, often just kg) or kilopond (kp) is defined as the force exerted by one kilogram of mass in standard Earth gravity. Although the gravitational pull of the Earth varies as a function of position on earth, it is here defined as exactly 9.80665 m/s². So one kilogram-force is by definition equal to 9.80665 newtons.[1]

The kilogram-force has never been a part of the International System of Units (SI), which was introduced in 1960. The SI unit of force is the newton.

Prior to this, the unit was widely used in much of the world; it is still in use for some purposes. The thrust of a rocket engine, for example, was measured in kilograms-force in 1940s Germany, in the Soviet Union (where it remained the primary unit for thrust in the Russian space program until at least the late 1980s), and it is still used today in China and sometimes by the European Space Agency.