- #1
Biker
- 416
- 52
Hello,
I have been doing high school physics for about 3 years now and I am perfectly fine with it. However, Something tricked me off few days ago. It is how we treat units. I was kind of hesitant to post this thread because I have seen multiple threads about it before and some member really posted useful links about it. It is a very common one.
I will define a "Unit" from what I understand. Unit is a measurement of physical quantity. We define how much a Kg weighs and we use it in our mathematics. We say we have 5 Kg which means we have something that weighs 5 times bigger than the unit we chose.
We can add similar units together. It makes intuitive sense.
2 Kg + 3 Kg = 5 Kg
we can subtract, divide such as density.
Now if I think about different units.
I can't simply add:
2 apples + 3 oranges = ... (No physical meaning)
"Multiplication is repeated addition" or we can see it is scaling which consists of addition.
So 2 apples * 3 oranges = shouldn't give you 6 apples x oranges.
However division makes sense. For example speed when I say 5m/s
I am just saying that for every sec passes I move 5 m.
and what about area? I define an area of an object to be made out of a square meter for example which is just a square with length of 1 m
So when I find the area of a rectangle with length 5 and width 2 I am simply stating
that I have 5 square meters for 1 width so you have 10 square meters
We reach to the same result as if we multiply units
5 m x 2 m = 10 m^2
I have read books about this and they just simply state that the derived quantity is just the product of the units without giving explanation
A summary of all this is, Why do we treat units as if they were variables?
Hopefully, Someone can set me straight because it is really irritating that I am not able to figure this out and it is kind of embarrassing :/
I have been doing high school physics for about 3 years now and I am perfectly fine with it. However, Something tricked me off few days ago. It is how we treat units. I was kind of hesitant to post this thread because I have seen multiple threads about it before and some member really posted useful links about it. It is a very common one.
I will define a "Unit" from what I understand. Unit is a measurement of physical quantity. We define how much a Kg weighs and we use it in our mathematics. We say we have 5 Kg which means we have something that weighs 5 times bigger than the unit we chose.
We can add similar units together. It makes intuitive sense.
2 Kg + 3 Kg = 5 Kg
we can subtract, divide such as density.
Now if I think about different units.
I can't simply add:
2 apples + 3 oranges = ... (No physical meaning)
"Multiplication is repeated addition" or we can see it is scaling which consists of addition.
So 2 apples * 3 oranges = shouldn't give you 6 apples x oranges.
However division makes sense. For example speed when I say 5m/s
I am just saying that for every sec passes I move 5 m.
and what about area? I define an area of an object to be made out of a square meter for example which is just a square with length of 1 m
So when I find the area of a rectangle with length 5 and width 2 I am simply stating
that I have 5 square meters for 1 width so you have 10 square meters
We reach to the same result as if we multiply units
5 m x 2 m = 10 m^2
I have read books about this and they just simply state that the derived quantity is just the product of the units without giving explanation
A summary of all this is, Why do we treat units as if they were variables?
Hopefully, Someone can set me straight because it is really irritating that I am not able to figure this out and it is kind of embarrassing :/