Newton’s First Law of Motion states that a body that sits still or moves with a constant velocity with respect to a motionless observer will have its status unaltered until acted upon by an unbalanced force. Such a change in motion is accompanied by an acceleration, which is a change of velocity of an object:
F = ma
If an object moves with a constant velocity through empty space, it will possess kinetic energy ( KE ), but its motion is unassisted by continuous energy inputs. One notable example of this type of motion is that of a photon of light which moves at a constant velocity ( c ) within a vacuum and whose quantum of energy is summarized as follows:
E = hf
Plank’s constant ( h = 6.62607015 x 10-34 J*Hz-1 ) is a constant of proportionality, and the energy ( E ) of a photon is directly proportional to the frequency of its electromagnetic wave. The SI unit of frequency is hertz ( Hz ). It is important to note that the frequency of an electromagnetic wave is inversely proportional to its wavelength ( 𝛌 ); thus, a photon with a large wavelength will have wave components that interact less frequently at a given point in space, and vice versa:
c = 𝛌f
And,
f = ( c / 𝛌 )
Substituting of ( f ) into the photon energy equation yields the following result:
E = hc / 𝛌
Contrary to photons, objects that move with a constant velocity against a source of resistance ( Ex. friction ) do so at the expense of work ( W ). The energy that flows into such systems must occur at an energetically favorable rate. This threshold energy per unit of time flowing into a system is defined as power ( P ). The SI unit of power is the watt ( W ), which itself is comprised of the SI units of joules ( J ) and seconds ( s ):
P = ( J / s )
Recall that the voltage ( V ) of a simple electrical system is comprised of the SI units of joules and coulombs ( C ):
V = ( J / C )
Additionally, the current ( I ) of a simple electrical system describes how many coulombs of charge flow past a point-of-reference in a second:
I = ( C / s )
We arrive at our much-sought-after equation for power within an electrical system as follows:
P = ( C / s )( J / C ) = ( J / s )
And,
P = IV
Using the ohm’s law derivative of voltage, we may expand this expression of power to other useful forms:
V = IR
( V / R ) = I
P = ( V / R )( V ) = ( V2 / R )
And likewise,
P = ( I )( IR ) = I2R
The latter expression is commonly used to determine what power losses will occur within a system in relation to its current and the resistance the current will encounter during its travels.
RENAISSANCE PHYSICS 