Why is the joule, the SI unit of energy, also the appropriate unit for measuring heat?

1 Answer
May 6, 2017

Answer:

1 Joule = 1 #Kgm^2/s^2# a complex unit derived from the definition of work.

Explanation:

The definition of work is a force acting over a distance.
=> Work = Force x Distance = F x d

From Newton's 2nd Law of Motion, Force = Mass x Acceleration
=> F = m x a

Substituting m x a for F in the Work formula => Work = m x a x d

The SI Unit for mass = #"Kilograms"(Kg)#, acceleration #((meters)/(second)^2)# =#(m/s^2)# and distance = #meters (m)#.

Substituting into Work = mass x acceleration x distance

= #(Kg)(m/s^2)(m)# = #Kgm^2/s^2# = #"Joule"#.

The other unit for heat quantities is the 'scientific calorie', or calorie (c) ; not to be confused with the neutritional calorie (C) (= 1000 scientific calories, or 1 Kilocalorie). The relationship between the two energy terms is as follows ...

1 calorie = 4.184 joules