*Hannah-Louise asked the Naked Scientists:*

I have been learning about physics and i got confused and my teacher wont explain why and I was wondering if you could help me, here is my question: Why can energy be lost and transferred but it can't be destroyed or created?

In

mechanics energy conservation comes from the

homogeneity of time: given the postulate that every instant of time is equivalent, then energy conservation is proved mathematically: you write energy H as: H = Σ

_{i}p

_{i}q

_{i}' - L(q

_{i},p

_{i},t) then you evaluate dH/dt using the Hamilton's equations:

q

_{i}' = ∂H/∂p

_{i}p

_{i}' = -∂H/∂q

_{i}(the ' means time derivative)

and the fact that, if time is homogeneous, then ∂L/∂t is = 0; the result is zero, so energy is conserved, so it cannot be destroyed or created.