Is there any physical quantity having two different units?

In summary, the conversation discusses the possibility of a physical quantity having two different units or formulas under different conditions. Examples such as velocity, torque, and energy are mentioned, showing that different disciplines may use different units for the same physical quantity. The concept of distributed forces is also introduced, where the same unit can be applied to different physical quantities. However, the conversation also highlights that if a physical quantity has different units, formulas, and applies to different conditions, it cannot be considered as the same quantity.
  • #1
Aaditya Jain
4
0
Is there any physical quantity having two different units or can it be possible that a physical quantity have two different units?
 
Physics news on Phys.org
  • #2
Hi Aaditya,
Not quite sure what you are asking?
Velocity uses two units, such as meter / sec - a length unit and a time unit.
 
  • #3
Good to hear from you. I am saying can a quantity have two different formula's having different units, if it acts under different conditions?
 
  • #4
A quantity such as distance can have units of meters or units of feet.
 
  • #5
The base units have to be the same but there are plenty of examples where different disciplines use different units. One well known example would be the use of Joules (J) and electron Volts (eV) for energy of particles. eV is very convenient because the charge on every electron is the same so the accelerating Voltage is a very handy measure to use. We also describe many EM waves in terms of wavelength and frequency - depending on convenience.
The list goes on.
 
  • #6
Aaditya Jain said:
Is there any physical quantity having two different units or can it be possible that a physical quantity have two different units?

In the geometrised units of GR, time and mass can be measured in units of length. The mass of the Sun, for example, is about ##3km##.
 
  • #7
There‘s the case of torque, which is measured in N m (Newton meters). Formally equivalent to energy (1 N m = 1 J), but you have to integrate torque against angular displacement to calculate work. I had always found this curious in high school.
 
  • Like
Likes DaveE, arivero, fresh_42 and 1 other person
  • #8
Aaditya Jain said:
I am saying can a quantity have two different formula's having different units
Maxwell’s equations have both different units and different formulas in SI units and in CGS units.
 
  • #9
Aaditya Jain said:
Good to hear from you. I am saying can a quantity have two different formula's having different units, if it acts under different conditions?

This still doesn't explain anything.

The electric field strength can be written in units of V/m or N/C. Are these "different" enough for you?

Zz.
 
  • #10
I mean to says different unit in dimension. Means, can it be possible that unit of a physical quantity equals to kgm2/s2 and kgm3s5, if it acts under different conditions.
 
  • #11
256bits said:
Hi Aaditya,
Not quite sure what you are asking?
Velocity uses two units, such as meter / sec - a length unit and a time unit.
I mean to says different units in dimension. Means, can it be possible that a physical quantity has unit equals to kgm2/s2 and kgm3s5, if it acts under different conditions.
 
  • #12
Yes. For example in quantum mechanics wave function ##\psi(\vec{r},t)## depends on dimension of problem. In one dimensional system it is ##L^{-1/2}##, in two dimensional is ##L^{-1}## and in three dimensional is ##L^{-3/2}##, where ##L## is lenght.
 
  • Like
Likes 256bits
  • #13
Aaditya Jain said:
I mean to says different units in dimension. Means, can it be possible that a physical quantity has unit equals to kgm2/s2 and kgm3s5, if it acts under different conditions.
Well it won't be the same physical quantity proper if the units are different.

But as @LagrangeEuler has replied, we can state something similar depending.
As an example,
Force acting at a point would be in Newtons.
An extended force could be expressed as Nt/m, such as that acting over a certain length of beam.
Or as Nt/m2 if the force is extended over a surface area.
These are called distributed forces.
 
  • #14
suremarc said:
There‘s the case of torque, which is measured in N m (Newton meters). Formally equivalent to energy (1 N m = 1 J), but you have to integrate torque against angular displacement to calculate work. I had always found this curious in high school.
I think that's a good example of two different physical quantities having the same units ( as distinct from two different units applying to the same physical quantity )
The difference between our definitions of torque and energy is that in the former case the relevant component force and distance are at 90 degrees to each other and in the latter case they are in the same direction.
 
  • #15
If they had different formulas, different units and apply to different conditions, by what logic would you even call them "the same quantity"?
 
  • Like
Likes Vanadium 50 and suremarc
  • #16
Dadface said:
The difference between our definitions of torque and energy is that in the former case the relevant component force and distance are at 90 degrees to each other and in the latter case they are in the same direction.
For the maximum values, what you say about the outcome of the definitions is true; but that's not even relevant.
 
  • Like
Likes nasu
  • #17
Mister T said:
For the maximum values, what you say about the outcome of the definitions is true; but that's not even relevant.
Sorry I don't understand your comment. Energy and Torque are completely different quantities which can both be expressed in the same units. But why "for the maximum values"?
 
Last edited:
  • #18
Dadface said:
But why "for the maximum values"?
These are the conditions under which you get the maximum values:

Dadface said:
The difference between our definitions of torque and energy is that in the former case the relevant component force and distance are at 90 degrees to each other and in the latter case they are in the same direction.
 
  • #19
Vitamin D is measured in functional units. If you immerse a half naked human in sunlight for a half hour, that human's skin will produce 20,000 units of cholecalciferol (nubile viamin D).
One mg of Vitamin D also equals 40,000 units. A tiny bit goes a long way.
The unit is a functional element while a milligram is your Newtonian classical mass.
 
  • #20
Dadface said:
The difference between our definitions of torque and energy is that in the former case the relevant component force and distance are at 90 degrees to each other and in the latter case they are in the same direction.
Mister T said:
These are the conditions under which you get the maximum values:
I'm still not sure what you mean by this. Whether the values be maximum or not the difference I described still holds. Also, I did not describe situations where you get maximum values, I referred to relevant "component" quantities which, depending on the relevant angles, can give values anywhere between the maximum possible and zero. I will try to describe the difference but very informally:

In the definition of work the distance referred to is the distance moved.
In the definition of torque the distance referred to is the distance between two points on whatever it is that the torque is applied to.
 

1. What is a physical quantity?

A physical quantity is a measurable property of a physical system, such as length, mass, time, or temperature.

2. Can a physical quantity have two different units?

Yes, a physical quantity can have two different units if it can be measured in two different ways or if it is expressed in different systems of measurement.

3. How do we convert between units of a physical quantity?

To convert between units of a physical quantity, we use conversion factors based on the relationship between the two units. For example, to convert from meters to feet, we multiply by 3.281.

4. Why do we use different units for the same physical quantity?

Different units for the same physical quantity may be used for historical reasons or because of different conventions in different countries. Additionally, some units may be more convenient or practical for certain applications.

5. Can a physical quantity have more than two units?

Yes, a physical quantity can have multiple units if it can be measured in multiple ways or if it is expressed in different systems of measurement. For example, velocity can be measured in meters per second, kilometers per hour, or miles per hour.

Similar threads

  • Other Physics Topics
Replies
1
Views
805
  • Other Physics Topics
Replies
19
Views
1K
Replies
50
Views
5K
Replies
8
Views
383
  • Other Physics Topics
Replies
9
Views
2K
  • Other Physics Topics
Replies
13
Views
2K
  • Other Physics Topics
Replies
1
Views
540
  • Other Physics Topics
Replies
7
Views
3K
  • Other Physics Topics
Replies
2
Views
587
  • Other Physics Topics
Replies
3
Views
12K
Back
Top