FILE No.148Unsolved
In a car with the windows fully closed, a helium balloon, not tied to the floor, floats near the ceiling. The car accelerates forward.
Which way does the balloon move?
If you get stuck, open the hints one at a time, in order.
What does the air in the car do when it starts moving?
Is a helium balloon lighter or heavier than air?
A light object moves toward the denser or the thinner air?
Which way does the balloon move?
Choose the answer closest to the truth.
Forward
The answer is "Forward."
When the car accelerates, the air in the car is pressed toward the back and bunches up there. When air gathers at the back, the pressure at the back rises, and the balloon, which is lighter than air, is pushed toward the front, where the pressure is lower.
A balloon moving backward would be the behavior of something heavier than air.
Because you think it will move backward like luggage.
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