MadSci Network: Physics |
The short answer here is perhaps that energy doesn't carry matter, but matter carries energy. But in order to see this, we need to understand something about what is meant when people talk about "energy". In physics, we usually think about two types of energy: kinetic energy and potential energy. That's a bit of a simplification, but an amazingly large chunk of what we know about physics is gotten simply from knowing the kinetic and potential energy functions of a system. Kinetic energy is the energy of motion. When an object moves relative to you, it has kinetic energy. The faster something moves, the more kinetic energy it has. Also, if two objects are moving with the same speed, the one with larger mass has more kinetic energy. An object which is not moving relative to you has zero kinetic energy. As you probably know, the total energy of any system is conserved, that is, it does not change. If you push on something, and make it go faster, you have increased that objects kinetic energy. Since energy is conserved, the increased energy of the object (appearing as kinetic energy) must have come from some other place. This kind of "stored" energy is called potential energy, since it has the potential to create motion (note that this isn't the only way to create motion, since you can transfer kinetic energy from one object to another by colliding them together; the total energy still remains the same). Potential energy may appear in many different forms. In the example above, where you push on something to make it move, the potential energy is stored in chemicals in your muscles. Another simple example is a spring. If you stretch a spring, it now contains potential energy, for as soon as you let it go, it starts to move. Gasoline contains potential energy, which is converted to heat when it burns in your car, which your engine then changes into the kinetic energy of the car's motion. The Earth's gravity also has potential energy. When you hold up a ball, and then let it go, the gravitational potential energy is converted into the kinetic energy of the ball, as it falls faster and faster. Let's look at the examples you gave. Rather than say "wind is energy", it is more correct to say "wind carries energy". Wind is simply the motion of air, so it's energy is an example of kinetic energy, in this case, carried by the molecules of the air. Waves in water form as a combination of kinetic energy of the water and potential energy from gravity. So roughly speaking, we can say that matter carries energy, rather than the other way around. Obviously you need matter in order to have kinetic energy, and most of the examples above (muscles, gasoline, spring) also have kinetic energy somehow stored in matter. If you want to throw a monkey wrench into this nice scheme, you can bring up gravity, but that's a question physicists are still debating today.
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