Some time ago a heard that a truck filled with chickens would weigh the same if the chickens either are on the floor of the truck or if they are hovering just under the roof. The reasoning is that the chickens are part of the same «system» as the truck, so the whole «system» would always weigh the same, even if the objects inside it is not in contact with it physically. Can someone explain what is meant by this «system» and if this is a true statement?
Thank you!
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In physics there are two types of systems: open systems and closed systems. The exact system is determined by the physicist working on the problem, though is usually pretty obvious for a given problem.
A closed system is one where nothing can enter or exit, such as your truck.
An open system allows energy and/or matter to enter or exit. A relevant example might be a railroad cattle car.
As for birds on a truck, that was [MythBusters Season 5, Episode 9](https://youtu.be/lVeP6oqH-Qo)
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