Why does “torque” have 2 different units?












1














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







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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
















1














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







share|cite|improve this question




















  • 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














1












1








1







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







share|cite|improve this question















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






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




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edited 4 hours ago







sparpo

















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














  • 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










2 Answers
2






active

oldest

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3














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.






share|cite|improve this answer





















  • 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



















3














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.






share|cite|improve this answer





















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    2 Answers
    2






    active

    oldest

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    2 Answers
    2






    active

    oldest

    votes









    active

    oldest

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    active

    oldest

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    3














    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.






    share|cite|improve this answer





















    • 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
















    3














    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.






    share|cite|improve this answer





















    • 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














    3












    3








    3






    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.






    share|cite|improve this answer












    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.







    share|cite|improve this answer












    share|cite|improve this answer



    share|cite|improve this answer










    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


















    • 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











    3














    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.






    share|cite|improve this answer


























      3














      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.






      share|cite|improve this answer
























        3












        3








        3






        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.






        share|cite|improve this answer












        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.







        share|cite|improve this answer












        share|cite|improve this answer



        share|cite|improve this answer










        answered 4 hours ago









        FarcherFarcher

        47.8k33796




        47.8k33796






























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