Question

What is the SI unit of energy?

Answer 1

The SI unit of energy is in joules.

We know from the work-energy theorem, that:

ΔE=WΔE=W

(Change in energy equals to work)

We know that work is defined as “force multiplied by displacement”. So we can substitute this into the equation.

ΔE=F⃗⋅d⃗

(Change in energy equals to force times displacement)

This is the tricky part. When we equate two expressions, we are saying that they share the same dimensions (same units). The SI unit for force is Newtons, and the SI unit for displacement is Meters. Therefore, the unit of energy and work is Newton-meters. We define 1 Newton-meter as 1 joule. This is how the unit of energy is derived.