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Ketchup Bottles

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I work at the bar, Murph's, on Friday and Saturday, and one of my tasks is to refill ketchup bottles. In order to get the ketchup to the neck of the bottle, I hold it by the bottom and spin it in a vertical circle. 

This works because of centripetal force. You might be saying, however, that centripetal force pulls objects towards the center of the circle. While this is true, it acts on less dense materials at a greater magnitude. Inside the ketchup bottle, there is only air and ketchup. Since air is less dense, it gets pulled towards the center, displacing the ketchup. 

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