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: How can I observe the role density plays?

Right after the Pentagon was hit, NEADS learned of another possible hijacked aircraft. It was an aircraft that in fact had not been hijacked at all. After the second World Trade Center crash, Boston Center managers recognized that both aircraft were transcontinental 767 jetliners that had departed Logan Airport. Remembering the "we have some planes" remark, Boston Center guessed that Delta 1989 might also be hijacked. Boston Center called NEADS at 9:41 and identified Delta 1989, a 767 jet that had left Logan Airport for Las Vegas, as a possible hijack. NEADS warned the FAA's Cleveland Center to watch Delta 1989. The Command Center and FAA headquarters watched it too. During the course of the morning, there were multiple erroneous reports of hijacked aircraft. The report of American 11 heading south was the first; Delta 1989 was the second. NEADS never lost track of Delta 1989, and even ordered fighter aircraft from Ohio and Michigan to intercept it. The flight never turned off its transponder. NEADS soon learned that the aircraft was not hijacked, and tracked Delta 1989 as it reversed course over Toledo, headed east, and landed in Cleveland. But another aircraft was heading toward Washington, an aircraft about which NORAD had heard nothing: United 93. United Airlines Flight 93 FAA Awareness. At 9:27, after having been in the air for 45 minutes, United 93 acknowledged a transmission from the Cleveland Center controller. This was the last normal contact the FAA had with the flight. Less than a minute later, the Cleveland controller and the pilots of aircraft in the vicinity heard "a radio transmission of unintelligible sounds of possible screaming or a struggle from an unknown origin." The controller responded, seconds later: "Somebody call Cleveland?"This was followed by a second radio transmission, with sounds of screaming.
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QUESTION: Two radio transmissions that included (possible) screaming came from which aircraft?

Light rays strike a reflecting surface. They are then reflected back. You can predict the angle of the reflected light. Imagine a ball bouncing off a surface. Light can do the same thing. That is, assuming the surface is shiny. So how do you know where light will go after it strikes a shiny surface? It depends on how the light initially strikes the shiny object. Light does not always go straight toward a surface. Therefore, not all light bounces straight back. Sometimes, light can hit a surface at an angle. The angle at which it strikes the surface tells us how it will bounce off. While light is different to a ball, they react in a similar manner. Many sports rely on knowledge of reflection. Pool players know a lot about reflection. They take great care when they strike the pool ball. They need it to go to a certain place. They know the angle it will hit the side of the pool table.
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QUESTION: Do pool players use the principles of reflection to get a ball to go to a certain place?

The factory is highly automated and designed to shift flexibly to produce many different kinds of chips to suit demand. "The diversity is the big difference with this plant," said Richard Doherty, president of Envisioneering, a research firm. "It gives IBM the capability to make so many different kinds of custom chips, and the world is going to custom chips." The 140,000-square-foot plant is a testament to advanced manufacturing technology. The 300-millimeter silicon wafers -- about the size of a standard pizza -- are shuttled around the facility in enclosed plastic pods, which ride on overhead tracks. They drop down from wires automatically into machines, sheathed in stainless steel and glass, for each stage of processing and fabrication. Throughout the 500 processing steps, which typically last 20 days, the wafers are not touched by human hands. The circuits etched into the chips are less than one thousandth the width of a human hair. Human operators are there to monitor the systems, catch errors and fine-tune the production process for maximum efficiency. Because each of the hundreds of processing machines is self-enclosed, and essentially airtight, the uniforms operators wear are less constricting than in the previous generation of chip plants, which looked like space suits. The operators at the East Fishkill factory wear light nylon uniforms, light blue shoe coverings and translucent hair nets made of paper. They look more like workers in a bakery. Yes, said Richard Brilla, director of the new facility, "but the donuts are a lot more costly here." Each wafer, holding hundreds of chips, is worth $6,000 to $10,000 apiece, depending on what insulation, circuitry and materials are used.
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QUESTION:
What is the brief summarization of the appearance of the operators' uniforms as described above?