字幕表 動画を再生する 英語字幕をプリント As you probably know by now, we’ve been working with Google and YouTube to answer ten of the most popular science questions asked on the internet. And I gotta hand it to you, because there are few questions that are as confounding and complex and fascinating and inspiring, as this one the collective consciousness has spewed forth: What is energy? I'm Hank Green, and this is the World’s Most Asked Questions. [Intro] Energy is everything. It’s everywhere. It’s one of the true constants of the universe, because as long as there’s been a universe, there’s been energy. And while it comes in lots of different forms that can seem different to us, they all amount to the same thing: Energy is the ability to do work. And work is just the act of displacing something by applying force. So, say you stomp on a stomp rocket. The force of your foot hitting the pedal is turned into the force of air leaving the cannon -- sending your rocket sailing. Or maybe you're enjoying a nice patty melt -- the energy from that food is broken down for all of the quadrillions of cells that you have to do all of the things that they have to do -- make copies of your DNA, assemble and repair proteins, transport materials from one place to another, make muscle cells contract -- you know, all the stuff of being alive. That rocket sailing, your cells toiling away, your phone or computer being on right now to watch me -- that’s all work being done. And the ability to do these things is inherent in everything around you. Even things that look inert, completely lacking in energy. Like this log. This log, for example, is chock full of chemical energy because it’s made up of combinations of carbon and hydrogen and oxygen formed into lignin, which is the stuff that makes up wood. All of the bonds between all of those atoms, in every molecule of lignin, contain energy. How do I know? Because if I were to apply enough extra energy, like as heat, to break those bonds -- it would release that chemical energy as fire. That chemical energy also the kind of energy you get from that patty melt -- your body is fueled by the chemical bond energy in sugars, fats, and proteins. But this log also contains nuclear energy! Each atom in this wood has a nucleus, made of protons and neutrons, and the energy that binds them together is one of the most powerful sources of energy in the universe. If you could split one of the atoms of carbon or hydrogen in this log, and rip those protons and neutrons apart, it’d release some of that energy. There’s so much nuclear energy in each atom that, if I could unleash all of it that's in this log? There’d be a giant smoldering crater where I’m standing and everyone in the town of Missoula, Montana would be dead. So, everything that’s made of atoms has nuclear energy locked up in it, but also, it turns out, that mass and energy are the same thing! You might have heard of this little equation that a German patent clerk came up with about a hundred years ago: E = mc2. And there are SO MANY OTHER KINDS of energy that I’d love to get into if we had the time ... .. but even though they may seem different, they can all be used to do work, whether it’s driving a turbine, or moving a engine piston, or allowing the screen on your tablet to glow. Or, if it’s that most mysterious of energies, dark energy, causing the universe to expand more than it seems like it should. But here’s the thing to remember. Once the work is done, the energy isn’t done. Because energy never goes away. It can never be destroyed, and in the same way, it can never be created. It can only be transferred from one source to another -- like, how the energy in the plants and animals that were in the patty melt were transferred into you -- or it can be transferred from one form into another -- like the chemical energy in the wood being transferred to light and heat as fire. You could think of the universe as a constant flow of energy, and we are just little pit stops along the way. Everything your body is doing right now -- whether it’s your lungs absorbing oxygen, your heart pumping blood, your brain cells firing as you watch me and learn things -- all those things are using recycled energy that’s been around since the origin of the universe. And by simply being alive, you’re releasing that energy back into the environment around you, to be used by other things in other ways. So Internet, to answer your question: Energy is everything. And for those of you who answered our questions on our SciShow survey, where you feel like you get your energy may be keeping you up at night. Survey takers who have a hard time falling asleep nearly every night get their energy from knowledge first, second from purpose. Least likely? From exercise. Of all the fascinating questions in the world, what question do you want to see answered most? Let us know on Facebook or Twitter or down in the comments down below and we will aim to answer those questions in a new video at the end of the month.