Why can't matter or energy be created nor destroyed?

Energy Can Neither Be Created Nor Destroyed ... The law of conservation of energy, also known as the first law of thermodynamics, states that the energy of a closed system must remain constant—it can neither increase nor ... Even mass is a form of energy, as Albert Einstein's famous E = mc2 showed. read more

Kinetic energy is the energy of its motion when it starts rolling. The sum of these is called mechanical energy. The heat in a hot object is the mechanical energy of its atoms and molecules in motion. read more

One of the interesting things about physics are how conserved quantities arise from symmetries about our universe. This is a mathematical result called Noether’s Theorem. read more