Pressure Differentials - Helium Balloon in Fish Tank (Chris Kipp)

Author

Chris Kipp

Principles Illustrated

• Density

• Buoyancy

Standards

Density and Buoyancy

8. All objects experience a buoyant force when immersed in a fluid. As a basis for understanding this concept:

8.c Students know the buoyant force on an object in a fluid is an upward force equal to the weight of the fluid the object has displaced.

Questioning Script

Prior knowledge & experience:

Students know that objects with large inertia will resist changes in motion. Students know that dense objects suspended from a string will fall behind when the string is accelerated forwards.

Root question:

I'm going to hang a tennis ball and a helium balloon from the inside of this fish tank. How will these two objects behave when I accelerate the fish tank forwards?

Target response:

When you create a pressure differential, dense objects sink relative to less dense objects.

1. The tennis ball falls opposite the direction of the accelerating force because it is more dense than the air around it.

2. The helium balloon falls the same direction as the accelerating force because it is less dense than the air around it.

Common Misconceptions:

1. All objects will move opposite the accelerating force because they all have the same inertia.

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