
Next time you throw a ball in the air, and it doesn't fly off into outer space, thank gravity. Right now, you and everything in the room where you are, is getting pulled down by gravity. If you don't believe it, push a book of your desk. It will go plummeting toward the center of the Earth. It's gravity. The Earth's mass, the stuff it's made of, creates gravity. It's pulling down on you and every other object you can see; it's even pulling down on the air and the ocean. Not only that, you and every atom of every thing around you has gravity. So, the objects and atoms are all, ever so slightly, pulling up on the Earth! Without gravity, there would be no weight. When you step on a bathroom scale, the scale is getting squeezed between you and the Earth. The scale measures how strong this mutual attraction is. Gravity makes a force that pulls objects together. Not only is gravity pulling on every atom and molecule of everything around us, it pulls over huge, gigantic di
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E11993 · 26m
Things that fly need air. Even though we walk through it, breathe it, and sneeze it, air seems to be a whole bunch of nothing. But air is there, and it's powerful. Balloons inflate because air presses on the insides and outsides of the balloon. Air pressure in tires supports the weight of bikes, buses, trucks, cars, and planes. But air doesn't need to be inside something to exert pressure. Air that moves around pushes, too. What do birds, planes, kites, Frisbees, and helicopters have in common? They fly because moving air creates lift, or a push up. Airplane wings are shaped to push air down. The momentum of the air going down pushes wings up. Air above the wing gets going faster than the air underneath. Fast-moving air zips along, without pushing as hard side to side or up and down. The slow air pushes up from below harder than the fast air pushes down from above ... and you're airborne! Every flying thing, from the tiniest flying insect to the biggest airplane, us
E21993 · 26m
Don't just go with the flow. Settle down on the crust. Imagine a world without any crust. There would be no pies, just goopy filling, no bread, no hamburger buns, and no you or me. That's right. You, and every living thing we know of, live on or in the Earth's crust. And, living things need the Earth's crust to survive. Let's look at the science of the surface. By carefully studying the Earth's surface, scientists have discovered that the Earth is made up of gigantic layers. At the center of the Earth, there is a core – a big ball of solid metal mostly iron. The core is surrounded by a layer of liquid iron and other minerals. We usually just call it the outer core. The next layer, around the outer core is called the mantle. You may have seen a mantle above a fireplace. Well, the mantle is above the Earth's hot core places. The mantle is gooey hot nearly melted rock that flows the way asphalt does on a hot summer day. Scientists often say that the mantle is plastic. It
Breakthrough: The Ideas That Changed the World
2019 · ★ 7.8