# Helium balloon centrifugal force

gracedescent
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.

## Answers and Replies

Homework Helper

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?

gracedescent

foward, yes?

Homework Helper

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

gracedescent

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