What you seem to be asking can be found by considering the law of conservation of energy. The energy we encounter and use in our everyday lives has always been with us since the beginning of the universe and always will be with us. It just changes form.<br /><br />Energy can be found in many systems (like ice cream falling off a cone and landing on a warm summer pavement….that is a system of energy transfer) and in many forms. <br /><br />Energy might be most simply described as having 2 forms that would include:<br /><br />1. Potential energy in objects at rest that will make them move if resistance (opposition to motion) is removed. <br /><br />2. Kinetic energy in objects that are moving. <br /><br />Please note that all matter, right down to basic molecules and atoms, has a huge amount of energy, as Einstein's E = mc^2 pointed out. Energy can also travel in the form of electromagnetic waves, such as the light you asked about that hits a wall. Electromagnetic waves are also seen as heat, radio, and high energy rays. <br /><br />Energy is constantly flowing and in flux. Indeed, if you have recently eaten (or not) your body is using metabolic energy. Rub your hands together. What is the energy transition? Well, you used your metabolic energy to rub your hands together and in so doing turned metabolic energy into mechanical energy. Your hands, I bet, “heated” up. The “heat-up” occurs when the mechanical energy turned into heat energy. <br /><br />So energy can change form, but where did that energy ultimately come from? Consider a series of everyday occurrences. A skate-board & rider are rolling down a steep driveway, transferring potential energy into kinetic (movement) energy. The skate-board got its potential energy (energy due to position related to gravity) by the rider using metabolic energy to move the board. The motion of the rider’s feet used mechanical energy to push against the ground, which moved the 4 wheels. The rider's metabolic energy came from chemical energy