When it falls back to the ground that energy will become kinetic energy again, E=0.5mv 2 (where m is the stone’s mass and v is its velocity). If that spring tosses a stone into the air, then at the top of its flight it will have converted all of that energy into gravitational potential, in the amount of E = mgh (mass of the stone times the acceleration of gravity times height). If that motor is used to compress a spring, then the energy stored in the spring is E=0.5kA 2 (where k is a spring constant, and A is the distance it’s compressed). If that electrical energy runs a motor, then the energy used is E = VIT (voltage times current times time). If those photons then fall onto a solar panel, that light energy can be converted into electrical energy. If that energy travels from the Sun to the Earth as light, then each photon of that light carries E=hν (Planck’s constant times frequency), of it. If fusion in the Sun releases energy*, then the amount released is E = (Δm)c 2 (where Δm is the change in mass between the hydrogen input and helium output and c is the speed of light). We can measure each of them, and we know that the total value between all of the various forms stays constant, and just like every other every constant, measurable thing it gets a name energy. There’s this quantity, that takes a lot of forms (physical movement, electromagnetic fields, being physically high in a gravitational well, chemical potential, etc., etc.). So, energy can change from one form into another into another into another, etc., but the question remains: what is energy? The answer to that is a little unsatisfying. Some form of energy without matter: that happens. It’s “matterless”, sure, but that doesn’t mean that electromagnetic fields (light) are any closer to being pure than, say, gravity fields (another, very different, massless form of energy). Light is about the closest anything comes to being pure energy, but it’s not pure energy so much as it’s one of the several kinds of energy that isn’t tied up in matter. For example, when “energy is released” in an explosion (most explosions) that energy mostly takes the form of kinetic energy (things moving and heat).
“Pure energy” shows up a lot in fiction, and most sci-fi/fantasy fans have some notion of what it’s like, but it isn’t a thing you’ll find in reality.Įnergy comes in a hell of a lot of forms, but they’re all pretty mundane.
0 kommentar(er)
