Helium balloon centrifugal force

AI Thread Summary
When a car decelerates, a helium balloon tied inside will swing backward instead of forward, contrary to typical expectations. This occurs because, in a decelerating frame of reference, the effective direction of gravity shifts forward. The helium balloon, which naturally rises against gravity, will respond to this altered gravitational pull by moving in the opposite direction. Thus, as the car slows down, the balloon appears to float backward. Understanding this behavior relies on the equivalence principle, which equates acceleration with gravitational effects.
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Helium balloon "centrifugal" force

Homework Statement


Assume that you are driving down a straight road at a constant speed. A helium-filled balloon is tied to a string that is pinned to the front seat. Which way will the balloon swing when you apply the brakes? Explain why.


Homework Equations


Not a calculation.


The Attempt at a Solution


Normally the object would try to sustain its motion and would swing foward. However, the helium balloon must change this scenario? Thanks.
 
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The easiest way to solve this problem would be to apply the equivalence principle, which says that in an accelerating reference frame, acceleration is indistinguishable from gravity. So inside the decelerating car, it feels as if gravity has a component forwards. Which way would the balloon move if a component of gravity goes forward?
 


foward, yes?
 


No. Helium balloons normally go against gravity, right? If the direction of "gravity" changes, the balloon will still go opposite gravity.
 


They go the opposite of gravity? They float you mean? Hmmmmph, yes; I think I understand where you are coming from now.
 

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