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.

Question: "Based on the explanation in the article, why do you expect to happen with the water and oil?"

Response: "The more dense substance will rise"

A: no

Energy is stored in chemical compounds. This energy is called chemical energy. Chemical energy is a form of potential energy. When bonds between atoms are broken, energy is released. The wood in fireplaces has chemical energy. The energy is released as heat and light when the wood burns. Most living things get their energy from food. When food molecules are broken down, the energy is released. It may then be used to do work, like playing ball or studying science. If you have ever heard, "Eat a good breakfast", thats why. You need energy to do things during the day. To do those things you need energy. You get your energy from the food you eat. That energy is stored in your body until you need it. How did you get to school today? If you walked, you used chemical energy from the food you ate. What if you rode the bus or were driven in a car? Where did that energy come from?

Question: "How is the energy from potential energy released?"

Response: "By chemical compounds"

A: no

American Airlines Flight 11: FAA Awareness. Although the Boston Center air traffic controller realized at an early stage that there was something wrong with American 11, he did not immediately interpret the plane's failure to respond as a sign that it had been hijacked. At 8:14, when the flight failed to heed his instruction to climb to 35,000 feet, the controller repeatedly tried to raise the flight. He reached out to the pilot on the emergency frequency. Though there was no response, he kept trying to contact the aircraft. At 8:21, American 11 turned off its transponder, immediately degrading the information available about the aircraft. The controller told his supervisor that he thought something was seriously wrong with the plane, although neither suspected a hijacking. The supervisor instructed the controller to follow standard procedures for handling a "no radio" aircraft. The controller checked to see if American Airlines could establish communication with American 11. He became even more concerned as its route changed, moving into another sector's airspace. Controllers immediately began to move aircraft out of its path, and asked other aircraft in the vicinity to look for American 11. At 8:24:38, the following transmission came from American 11: American 11: We have some planes. Just stay quiet, and you'll be okay. We are returning to the airport. The controller only heard something unintelligible; he did not hear the specific words "we have some planes." The next transmission came seconds later: American 11: Nobody move. Everything will be okay. If you try to make any moves, you'll endanger yourself and the airplane.

Question: "What did the controllers do when American 11 left the first controller's airspace and moved into another sector?"

Response: "They moved other flights out of its path and asked other area planes to look for American 11"

A:
yes