Density is also an important physical property of matter. The concept of density combines what we know about an objects mass and volume. Density reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter is more dense. Differences in density of matter explain many phenomena. It explains why helium balloons rise. It explains why currents such as the Gulf Stream flow through the oceans. It explains why some things float in or sink. You can see this in action by pouring vegetable oil into water. You can see a colorful demonstration in this video.
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QUESTION: What are three examples of density given in the article?

How would the universe look without gravity? It would have no planets and no stars. Thats how it looked when it was young. When the universe was young, there was only gas and dust. From this gas and dust, everything we now see was made. How were stars and planets created from just gas and dust? The answer is gravity. The same gravity that holds you down on Earth. The same force that causes your pencil to roll off your desk. The same force that causes it to fall to the floor. The invisible force of gravity caused dust and gas particles to be pulled together. This force is what formed all the objects in our solar system. This force formed the smallest moons. It also formed our Sun. This force caused more than just our solar system to form. It caused all the other solar systems to form. It caused the formation of all the galaxies of the universe.
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QUESTION: What did role did gravity play in the creation of the universe?

I wondered if that were my case--if I rode out for honour, and not for the pure pleasure of the riding. And I marvelled more to see the two of us, both lovers of one lady and eager rivals, burying for the nonce our feuds, and with the same hope serving the same cause. We slept the night at Aird's store, and early the next morning found Ringan. A new Ringan indeed, as unlike the buccaneer I knew as he was unlike the Quaker. He was now the gentleman of Breadalbane, dressed for the part with all the care of an exquisite. He rode a noble roan, in his Spanish belt were stuck silver-hafted pistols, and a long sword swung at his side. When I presented Grey to him, he became at once the cavalier, as precise in his speech and polite in his deportment as any Whitehall courtier. They talked high and disposedly of genteel matters, and you would have thought that that red-haired pirate had lived his life among proud lords and high-heeled ladies. That is ever the way of the Highlander. He alters like a clear pool to every mood of the sky, so that the shallow observer might forget how deep the waters are.
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QUESTION: Who are the two people who "talked high and disposed of genteel matters"?

A flood occurs when a river overflows its banks. This might happen because of heavy rains. Floodplains In very flat regions, flood water may spread out on the surface of the land. It then slows down and drops its sediment. If a river floods often, a floodplain develops. A floodplain is an area where a thick layer of rich soil is left behind as the floodwater recedes. Thats why floodplains are usually good places for growing plants. They are very flat areas and they have very rich soils. The Nile River valley is a great example of a floodplain. Each year, the Nile River rises over its banks. This floodwater carries a lot of sediment. This sediment has been eroded off areas of land from upstream. This sediment is dropped as the water slows down after spreading across the land. What is left behind is a very rich soil. Thats why crops can be raised in the middle of a sandy desert. Natural Levees A flooding river often forms natural levees along its banks. A levee is a raised strip of sediments deposited close to the waters edge.
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QUESTION:
What may cause a river to flood and overflow its banks?