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Lec2 - Physics 101 • Today Chapter 3 Chapter 3 Linear...

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Unformatted text preview: Physics 101: • Today: Chapter 3 Chapter 3: Linear Motion Preliminaries • Linear motion is motion in a straight line. • Note that motion is relative : eg your paper is moving at 107 000 km/hr relative to the sun. But it is at rest relative to you. Unless otherwise stated, when we talk about speed of things in the environment, we will mean relative to the Earth’s surface. Clicker Question 1. The preserver upstream. 2. The preserver downstream 3. Both require the same. Suppose you and a pair of life preservers are floating down a swift river, as shown. You wish to get to either of the life preservers for safety. One is 3 meters downstream from you and the other is 3 meters upstream from you. Which can you swim to in the shortest time? Suppose you and a pair of life preservers are floating down a swift river, as shown. You wish to get to either of the life preservers for safety. One is 3 meters downstream from you and the other is 3 meters upstream from you. Which can you swim to in the shortest time? 1. The preserver upstream. 2. The preserver downstream 3. Both require the sam e. Answer: 3, same time. You, and both life preservers are moving with the current – relative to you before you start swimming, neither of the life preservers are moving. An analogy: We can think of things on earth as being in a “current” traveling at 107 000 km/h relative to sun. Speed • Speed measures “how fast” : Units: eg. km/h, mi/h (or mph), m/s meters per second, standard units for physics Speed = distance time Instantaneous vs Average Speed Things don’t always move at the same speed, eg car starts at 0 km/h, speed up to 50 km/h, stay steady for a while, and then slow down again to stop. Average speed = total distance covered time interval 50 km/h 0 km/h time speed average speed Eg. Carl Lewis once ran 100m in 9.92s. • What was his average speed during that run? Average speed = dist/time = 100m/9.92s = 10.1 m/s • How much distance did he cover per second, on average? 10.1 m, by definition of average speed • How did this relate to his top speed?...
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Lec2 - Physics 101 • Today Chapter 3 Chapter 3 Linear...

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