physics_135_winter_2018_lecture_1C - Racquetball Striking a Wall Physics for the Life Sciences Physics Tools Lecture#1C Stewart Hall Mt Etna A Nice

# physics_135_winter_2018_lecture_1C - Racquetball...

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Physics Tools Physics for the Life Sciences Lecture #1C Racquetball Striking a Wall Mt. Etna Stewart Hall
A Nice Way to Use Vectors Relative velocity: sometimes a velocity is ‘made up’ of several parts: you walk through a train while it moves over the track Your total velocity is a sum of several components v person-ground = v person-train + v train-ground ! v person-train v train-ground v train-ground ! v person-train v person-ground y x z v PG = v PT + v TG OR Note: ! v PG = ! v GP , ! v PT = ! v TP , and ! v TG = ! v GT
In Two Dimensions It’s the Same Imagine a dog swimming across a river The dog swims at 1.2 [m/s] relative to the water The water flows left at 1.2 [m/s] If the dog “heads straight across” (swims relative to the water with his nose pointing to the opposite shore), it travels at 45º relative to the shore . v dog-water v dog-shore v water-shore v dog-water v water-shore v dog-shore = v dog-water + v water-shore or v DS = v DW + v WS y x z
Imagine a dog swimming across a river o The dog can swim at 2 [m/s] relative to the water o The water flows West at 1 [m/s] relative to the shore What direction must the dog swim to end up directly across the river as shown?