Derivations of SI Units in my High-School Physics formulas.

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The discussion focuses on the derivations of SI units for various high school physics formulas, specifically within the context of the New South Wales curriculum in Australia. Key formulas include frequency (f = 1/t), work (W = Fs), charge (q = I/t), resistance (R = V/I), voltage (V = E/q), power (P = E/t), force (F = ma), magnetic flux (Ф = BA), and their respective derived units. Each formula is broken down to show how fundamental units like kilograms, meters, seconds, amperes, and joules relate to one another. The thread emphasizes that these derivations are intended for introductory physics without calculus, making them accessible for high school students. Overall, it serves as a playful exploration of unit derivations relevant to foundational physics concepts.
f3nr15
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I was bored so I make fun with derivations of SI units of many Physics formulas.
Note, this should just be called "introductory physics", that means NO calculus (but rate of change designated by the delta symbol) and motion is in one or two directions only.
This is high school physics level in Australia only (State NSW to be more precise).

Here goes, I hope I'm right.


f = 1/t

Unit: Hz (Hertz)
Derived Unit(s): s-1 (per second)



W = Fs

Unit: J (Joule)
Derived Unit(s): N m (Newton-metre)
Further Derived Unit(s): kg m s-2 x m = kg m2 s-2 (kilogram-metre squared per second squared)

(N = kg m s-2)



q = I/t (I = q/t)

Unit: C (Coulomb)
Derived Unit(s): A s (Ampere-second)

(A = C s-1)



R = V/I [V = IR (Ohm's Law)]

Unit: Ω (Ohm)
Derived Unit(s): V A-1 (Volts per ampere)
Further Derived Unit(s): kg m2 s-3 A-1 x A-1 = kg m2 A-2 s-3 (kilogram-metre squared per Ampere squared-second cubed)

(V = kg m2 s-3 A-1)



V = E/q (V = ΔPE/q)

Unit: V [Voltage (Potential Difference or Electromotive force (emf))]
Derived Unit(s): J C-1
Further Derived Unit(s): kg m2 s-2 x A-1 s-1 = kg m2 A-1 s-3 (kilogram-metre squared per Ampere-second cubed)

(J = kg m2 s-2 & C = A s)



P = E/t

Unit: W (Watt)
Derived Unit(s): J s-1 (Joules per second)
Further Derived Unit(s): kg m2 s-2 x s-1 = kg m2 s-3

(J = kg m2 s-2)



F = ma (Newton's Second Law)

Unit: N (Newton)
Derived Unit(s): kg m s-2 (kilogram-metre per second squared)

(a = m s-2 = N kg-1)



B = F / LI (F = LIB)

Unit: T (Testla)
Derived Unit(s): N m-1 A-1 (Newton per metre-Ampere)
Further Derived Unit(s): kg m s-2 x m-1 x A-1 = kg A-1 s-2 (kilogram per Ampere-second squared)

(N = kg m s-2)

&

Wb m-2 (Weber per metre squared)



Ф = BA

Unit: Wb (Weber)
Derived Unit(s): T m2 (Testla-metre squared)
Further Derived Unit(s): kg A-1 s-2 x m-2 = kg A-1 m-2 s-2 (kilogram per Ampere-metre squared-second squared)

(T = kg A-1 s-2)
 
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Q should be I*t. I'm sure you knew that.
 
Meir Achuz said:
Q should be I*t. I'm sure you knew that.

My bad ... but I can't edit my thread !
 
Last edited:
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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