Why does “torque” have 2 different units?
On various websites I see torque expressed as kgm but I was always taught torque is Nm or kgm^2/s^2. These are clearly not the same, so why are they called the same and when do I use one or the other?
angular-momentum torque units
asked 4 hours ago
sparposparpo
83
add a comment |
On various websites I see torque expressed as kgm but I was always taught torque is Nm or kgm^2/s^2. These are clearly not the same, so why are they called the same and when do I use one or the other?
angular-momentum torque units
asked 4 hours ago
sparposparpo
83
2
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago
add a comment |
On various websites I see torque expressed as kgm but I was always taught torque is Nm or kgm^2/s^2. These are clearly not the same, so why are they called the same and when do I use one or the other?
angular-momentum torque units
asked 4 hours ago
sparposparpo
83
On various websites I see torque expressed as kgm but I was always taught torque is Nm or kgm^2/s^2. These are clearly not the same, so why are they called the same and when do I use one or the other?
angular-momentum torque units
angular-momentum torque units
asked 4 hours ago
sparposparpo
83
asked 4 hours ago
sparposparpo
83
edited 4 hours ago
sparpo
asked 4 hours ago
sparposparpo
83
asked 4 hours ago
sparposparpo
83
asked 4 hours ago
sparposparpo
83
83
2
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago
add a comment |
2
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago
2
2
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago
add a comment |
2 Answers
2
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Those other sources were probably referring to kilogram-force instead of Newtons. Given the constant conversion between mass and weight on Earth (i.e., $g = 9.8,textrm{m/s^2}$), mass and weight units are often used interchangeably in non-scientific contexts. So, torque can be expressed in kgf-m, where 1 kgf is the weight of 1 kg on Earth's surface. Notice that this is a multiplication, not a division. Units of kgf/m would be completely incorrect.
answered 4 hours ago
Mark HMark H
12.1k22340
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
add a comment |
The non SI unit is often written as 1 kg-m and is equal to 9.8 N m.
In such a case the 1 kg refers to the unit 1 kg force which is the weight of one kilogram.
Another unit is the Imperial (and US) unit the pound-foot which is equal to approximately 1.36 N m.
Here the unit of force is the pound force.
answered 4 hours ago
FarcherFarcher
47.8k33796
add a comment |
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2 Answers
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2 Answers
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Those other sources were probably referring to kilogram-force instead of Newtons. Given the constant conversion between mass and weight on Earth (i.e., $g = 9.8,textrm{m/s^2}$), mass and weight units are often used interchangeably in non-scientific contexts. So, torque can be expressed in kgf-m, where 1 kgf is the weight of 1 kg on Earth's surface. Notice that this is a multiplication, not a division. Units of kgf/m would be completely incorrect.
answered 4 hours ago
Mark HMark H
12.1k22340
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
add a comment |
Those other sources were probably referring to kilogram-force instead of Newtons. Given the constant conversion between mass and weight on Earth (i.e., $g = 9.8,textrm{m/s^2}$), mass and weight units are often used interchangeably in non-scientific contexts. So, torque can be expressed in kgf-m, where 1 kgf is the weight of 1 kg on Earth's surface. Notice that this is a multiplication, not a division. Units of kgf/m would be completely incorrect.
answered 4 hours ago
Mark HMark H
12.1k22340
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
add a comment |
Those other sources were probably referring to kilogram-force instead of Newtons. Given the constant conversion between mass and weight on Earth (i.e., $g = 9.8,textrm{m/s^2}$), mass and weight units are often used interchangeably in non-scientific contexts. So, torque can be expressed in kgf-m, where 1 kgf is the weight of 1 kg on Earth's surface. Notice that this is a multiplication, not a division. Units of kgf/m would be completely incorrect.
answered 4 hours ago
Mark HMark H
12.1k22340
Those other sources were probably referring to kilogram-force instead of Newtons. Given the constant conversion between mass and weight on Earth (i.e., $g = 9.8,textrm{m/s^2}$), mass and weight units are often used interchangeably in non-scientific contexts. So, torque can be expressed in kgf-m, where 1 kgf is the weight of 1 kg on Earth's surface. Notice that this is a multiplication, not a division. Units of kgf/m would be completely incorrect.
answered 4 hours ago
Mark HMark H
12.1k22340
answered 4 hours ago
Mark HMark H
12.1k22340
answered 4 hours ago
Mark HMark H
12.1k22340
answered 4 hours ago
Mark HMark H
12.1k22340
12.1k22340
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
add a comment |
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
Yes, and in particular it is strictly speaking wrong - though commonly done, and moreover this shows exactly why you shouldn't do it - to write the unit kgf as "kg".
– The_Sympathizer
5 mins ago
add a comment |
The non SI unit is often written as 1 kg-m and is equal to 9.8 N m.
In such a case the 1 kg refers to the unit 1 kg force which is the weight of one kilogram.
Another unit is the Imperial (and US) unit the pound-foot which is equal to approximately 1.36 N m.
Here the unit of force is the pound force.
answered 4 hours ago
FarcherFarcher
47.8k33796
add a comment |
The non SI unit is often written as 1 kg-m and is equal to 9.8 N m.
In such a case the 1 kg refers to the unit 1 kg force which is the weight of one kilogram.
Another unit is the Imperial (and US) unit the pound-foot which is equal to approximately 1.36 N m.
Here the unit of force is the pound force.
answered 4 hours ago
FarcherFarcher
47.8k33796
add a comment |
The non SI unit is often written as 1 kg-m and is equal to 9.8 N m.
In such a case the 1 kg refers to the unit 1 kg force which is the weight of one kilogram.
Another unit is the Imperial (and US) unit the pound-foot which is equal to approximately 1.36 N m.
Here the unit of force is the pound force.
answered 4 hours ago
FarcherFarcher
47.8k33796
The non SI unit is often written as 1 kg-m and is equal to 9.8 N m.
In such a case the 1 kg refers to the unit 1 kg force which is the weight of one kilogram.
Another unit is the Imperial (and US) unit the pound-foot which is equal to approximately 1.36 N m.
Here the unit of force is the pound force.
answered 4 hours ago
FarcherFarcher
47.8k33796
answered 4 hours ago
FarcherFarcher
47.8k33796
answered 4 hours ago
FarcherFarcher
47.8k33796
answered 4 hours ago
FarcherFarcher
47.8k33796
47.8k33796
add a comment |
add a comment |
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2
Don’t trust websites for introductory physics help. There’s a lot of crap and noise out there. The one you were always taught is perfectly right!
– knzhou
4 hours ago
@knzhou I see this unit of torque kg/m , in the details of electric motors. They always give the torque of an electric motor in kg/m. Do they just call it "torque" but mean something else?
– sparpo
4 hours ago
@knzhou Actually "kg/m" was probably just a mistake on this website, they probably meant kg*m.
– sparpo
4 hours ago
It has any number of units, since there are any number of unit systems. In cgs it has unit $dyne cdot cm$. If you stick to a single unit system you cannot go wrong. My advise is mksi, so $Nm$.
– my2cts
4 hours ago
@sparpo, kg is a unit of mass, and N is a unit of force. kg-m is NOT a unit of torque. This usage no doubt comes from the usage of ft-lb in the English system, but what most people don't realize is that there are pounds-force and pounds-mass, and the two units differ by a factor of 32.2.
– David White
3 hours ago