Problem: 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: "How can I observe the role density plays?"

Answer: "By watching the animation or by adding oil to water yourself"
Answer: yes

Problem: LONDON, England (CNN) -- The most eagerly anticipated animated film this year hits big screens this weekend, as "The Simpsons Movie" opens worldwide. The Screening Room spoke to creator Matt Groening and writer Al Jean in London about everyone's favorite two-dimensional yellow family. Simpsons supremo Matt Groening with his creations at the film's premiere in Springfield, Vermont Matt Groening told the Screening Room that fans had driven the demand for the movie. "We've had fans clamoring for a movie for the past 18 years," he said. The film has taken four years to come to fruition, as writer Al Jean explained. "What really held us up for a long time was to have enough people to do the show and the movie," he said. "We talked for a while about doing the movie after the show is done, but the show is never done! So it really started in earnest in 2003, when we started working on this story that became the movie." Technology has also played its part. Jean continued, "The technology to do this film really wasn't even around five years ago. For example, there was this joke I once pitched and David Silverman, the director, started drawing and as I was pitching it, it went into the film and it was cut a day later. To go from pitch to cut in two days is pretty impressive." Its creators hope that "The Simpsons Movie" will both satisfy long-term fans and bring Homer and Marge's family to a new audience. Groening told the Screening Room, "This movie is designed to both honor the people who have loved the show all this time, so there's lots of little details for them in the movie, little characters and stuff who they know and love, but we also want people who don't know the family to not be completely confused. It is a complete movie experience, but again, we have a lot of little details that only the really, true die-hard fans are going to get." And fans can expect to be entertained by plenty of cartoon mishaps. Groening said, "When you see somebody fall off the roof in a live-action film, it's funny -- we all love it. But it's not as funny as when Homer falls off the roof.

Question: "Why was Jean impressed with the time it took for the joke he pitched to be cut?"

Answer: "It was much slower to cut than normal"
Answer: no

Problem: When you get sick, your body springs to action. Your body starts to fight the illness. Thats why you want to eat right and get plenty of sleep. You need a strong immune system to fight off illness. Plants dont have an immune system. That does not mean they do not get sick. Plants are affected by disease just like us. Typically, their first line of defense is the death of part of the plant. This prevents the infection from spreading. Many plants also produce special chemicals to fight disease. For example, willow trees produce a chemical to kill the bacteria. The same compound is used in many acne products. You can see a picture of a willow tree in Figure Plants may be smarter than we think. No, they cannot talk to each other. They may be able to send messages, though.

Question: "What are two ways plants can fight off disease?"

Answer: "Eat right and get plenty of sleep"
Answer:
no