I heard that if a car accelerates from rest, a balloon would move forwards instead of backward. Why is this? Science says it’s because of density, but I don’t get their explanation. It also seems like it’s violating newton’s first law.
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The air in the car “sloshes” back, just as your intuition tells you things in a car ought to do as the car accelerates. The balloon winds up going forward since that’s “easier.”
To replace the situation with one that perhaps feels much more intuitive, consider a tank half full of water. As the car accelerates the heavy water sloshes to the back of the tank, which means all of the air in the tank actually got pushed forward.
The balloon trick trips people up because we see the balloon and account for it as something that’s a real thing, while ignoring the air as another thing that’s in the car.
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