Rough surfaces create more friction than smooth surfaces. Thats why cars have tires. Its also why we use rubber mats in areas that might get wet. In your bathtub, you may even use No-Slip tape. No-slip is another way of saying the items has a lot of friction. In Figure 1.9, the blades of the skates are very smooth. Thats why you cant slide across ice with shoes. The soles of your shoes are much rougher than skates. The rougher surface of shoes causes more friction and slows you down. Heavier objects also have more friction. A heavy object presses down with more force. The surfaces are held together more tightly. This makes the surfaces harder to slide past each other. Did you ever try to push something heavy across the floor? Heavy objects are much harder to push than light objects.

What property does the surface of a rubber mat have that prevents us from slipping in wet areas?

Billy and Sally are brother and sister. Billy is seven and Sally is eight. Their mother, Deborah, likes to have Billy and Sally dress up in costumes and play a game where they are answering the telephone. Usually when they play the game, Billy answers the telephone in a loud voice, and Sally answers the telephone in a quiet voice. On Tuesdays, Billy answers in a quiet voice, and Sally answers in a loud voice. On Fridays, Billy answers in a loud voice and Sally in a quiet voice. Billy has blonde hair. Sally has brown hair. Deborah has blonde hair, and Billy and Sally's father, Bob, has brown hair. He tells them to eat lettuce every time that he sees them, so that they grow big and strong like he is. Deborah likes to add some sugar with the lettuce so that Billy and Sally know what it is like to have sweet tastes in their life. One day, a Wednesday, Billy throws some lettuce into Sally's hair. Deborah laughs an grabs some straw from their farm and puts it in Billy's hair. Billy and Sally live on a farm. They have a goat, named Joey, and a duck, named Quack. They sometimes play a game with the goat where they chase him around the farm. Other times, they play a game with Quack where they wave at Quack and laugh. They have a fun life growing up on the farm.

What color hair does everyone have in Billy and Sally's family?

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.
Which flight never turned off its transponder?