Puzzle | Car and Helium Balloon motion

Puzzle:

A Geek was in a car with a helium balloon on a string that is tied to the floor. The windows are closed. When she steps on the accelerator, what happens to the balloon: does it move forward, move backwards, or stay put?

Solution:

• When the car accelerates, the air is pushed backwards, just as your body is.
• This sends a the Helium balloon, which is lighter than air, forward.
• When the car brakes suddenly, the air piles up in front of the windshield.
• This sends the balloon backwards.
• Hence the Helium balloon moves in the direction of the acceleration of the car, i.e. and When the car moves backwards, the Helium balloon moves backwards.