Question

A spirit level contains a bubble in a liquid. The level is suddenly jerked forward. Relative to the spirit level and liquid, the bubble moves

• A. backwards, due to its inertia.
• B. backwards, due to a pressure gradient in the liquid.
• C. forward, due to its inertia.
• D. forward, due to a pressure gradient in the liquid.

Answer 1

The correct option is D forward, due to a pressure gradient in the liquid.

As the spirit level is jerked forward, the liquid moves backward relative to the spirit level due to its inertia. Hence, the bubble must move forward relative to the liquid and the spirit level.
Due to backward motion of liquid, there must be a pressure gradient in the liquid. It is this pressure gradient which supplies the force which moves the bubble forward.