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!
In: 1
The system in physics, it is a portion of the physical universe chosen for analysis. So it is the truck, the chicken, the air in it. There is not direct contact between the chickens and the truck but there is interaction via the air.
In that example, it is an enclosed compartment the chickens are in not just a wire cage exposed to the outside. If that was the case the weight would not be the same.
When the chickens stay up in the air there has to be an upward force equal to the force of gravity. Weight is the downward force of gravity on an object and to say still in the air you need to counteract it like by punching down air.
According to Newton’s third law “for every action (force) in nature, there is an equal and opposite reaction” so the upward force the chicken generates with the wings results in an equal downward force on the air. The air will push on more air and it will finally hit the floor of the truck and through its body of it to the tires and the ground.
So if you put a force sensor below wheels the force from gravity on the chicken will be translated to it. It does not matter if the chickens are flying or standing on the floor. The difference will just be if the air is involved in the force transfer or not.
Latest Answers