Physics: multiple choice (Density and buoyancy)

Question

In considering density and buoyancy, a helium balloon floats in air even as wood floats on water. A father was bringing home balloons for a party and had attached the balloons to the seat of a van so that they were floating freely on all sides without touching the ceiling. If he turns the car to the right with a large velocity which way will the balloons move?

 

 

a. To the right

b. To the left

c. They don’t move

Answer 1

This is an interesting question since there are two different forces to consider.

One force is as described by Joseph C. below.

However, there is another force acting in the opposite direction caused by the more dense air surrounding the balloons also moving to the left leaving the less dense balloons moving to the right due to buoyant forces.

The combination of these forces might mean the balloons would move to the right if the buoyant force is greater than the inertial force.

I recall seeing a demonstration of candles burning under a dome rotating on a turntable and seeing the flames point inward toward the center of the turntable. As hot air from flames tends to rise like the helium balloons, I believe the balloons will move to the right.

Answer 2

By turning to the right, the balloons will appear to move to the left relative to the car. The acceleration of the car into the turn will mean that the car will move into the turn at a greater rate than the contents of the car, including the driver.

 

This apparent motion to the left will be the result of the inertia, not the buoyancy, of the balloons. Their buoyancy will only serve to keep them suspended in air.