Why is Energy a Scalar? A Simple Explanation

[oneplusone]

I am having trouble understanding why energy is a scalar. (1/2 mv^2, mgh, 1/2kx^2, etc).
Can someone just briefly hit over why? I tried asking a few people but I still don't get it. Thanks.

 

[A.T.]

I am having trouble understanding why energy is a scalar. (1/2 mv^2, mgh, 1/2kx^2, etc).
Can someone just briefly hit over why? I tried asking a few people but I still don't get it. Thanks.

Because that's what is conserved.

 

[kith]

For every (continuous) symmetry a physical system inhibits, we have a conserved quantity. The translation invariance in 3 spatial directions leads to 3 momentum components which are conserved. The temporal translation invariance leads to energy conservation.

In relativity, the 3-vector of momentum is combined with energy to form the 4-momentum.