Question

A bubble of air released at the bottom of a pool of water becomes larger as it approaches the water surface. This is due to (1) decreasing pressure on the bubble as it rises (2) high temperature of water near the water surface (3) changing surface tension of the water (4) decreasing stability of the bubble with the height from the bottom

Short answer

Option 1: decreasing pressure on the bubble as it rises.

Step-by-step solution

Understanding the Scenario

A bubble of air is released at the bottom of a pool and becomes larger as it ascends toward the water surface.

Consider Pressure Changes (Option 1)

As the bubble rises, the pressure of the water surrounding it decreases. According to Boyle's Law, at constant temperature, the volume of a gas is inversely proportional to its pressure.

Analyze Temperature Effects (Option 2)

High temperature at the water surface might increase the bubble size. However, the temperature change in a pool is generally minimal and not sufficient to cause significant changes.

Evaluate Surface Tension (Option 3)

Changing surface tension affects the shape of the bubble but is less likely to influence the overall volume significantly as it rises.

Examine Bubble Stability (Option 4)

Decreasing stability of the bubble does not directly correlate with the bubble expanding in size as it ascends.

Conclude the Correct Option

Option 1 is the most plausible reason: the bubble of air becomes larger as it approaches the water surface due to decreasing pressure on the bubble as it rises.

Key concepts

Pressure Changes

When discussing why a bubble of air released at the bottom of a pool increases in size as it rises, understanding pressure changes is key. As the bubble ascends, the pressure exerted by the water on the bubble decreases. This can be explained by Boyle's Law, a fundamental principle in physics.
Boyle's Law states: \[ P_1V_1 = P_2V_2 \] where \(P_1\) and \(P_2\) are the initial and final pressures, and \(V_1\) and \(V_2\) are the initial and final volumes, respectively.
This relationship tells us that at constant temperature, the volume of a gas increases as the pressure decreases.
Therefore, as the bubble ascends and the pressure drops, its volume expands. This decrease in pressure is the primary reason the bubble grows in size.

Gas Volume

The volume of gas in the bubble changes due to the variations in pressure as it moves upward through the water. According to Boyle's Law, if the temperature remains constant, the volume of the air in the bubble will increase as the pressure decreases.
This happens because the gas molecules are less compressed as the external pressure decreases, allowing the bubble to expand.
In simpler terms:

• The deeper the bubble is, the higher the pressure around it.
• As the bubble rises, the pressure decreases.
• With the drop in pressure, the gas molecules in the bubble spread out, making the bubble larger.

Water Surface Tension

Surface tension affects the shape and stability of the bubble: it is the elastic tendency of water's surface, which makes it contract and resist external force. While surface tension can impact the bubble's shape, its role in changing the bubble's volume as it rises is minimal compared to pressure changes.
However, it's crucial to understand that:

• Surface tension tries to minimize the surface area of the bubble.
• As the bubble increases in size, the effects of surface tension become less significant compared to the large volume changes due to pressure.
• The interaction between surface tension and pressure helps the bubble maintain its spherical shape as it rises.

Bubble Dynamics

Bubble dynamics encompasses the behavior and movement of bubbles underwater. Several factors affect bubble dynamics, but pressure change is the most significant in the context of a bubbling rising in water. Other important factors include:

• Temperature: Higher temperatures can cause slight expansion, but pool water temperature changes are usually too small to matter greatly.
• Stability: As bubbles rise, they may become less stable due to deformation caused by water currents and turbulence. This doesn't significantly affect bubble volume.
• Shape: Initially small and perfectly spherical, bubbles can become more spherical or slightly deformed as they rise due to changing surface tension and pressure dynamics.

Understanding these dynamics allows us to grasp why pressure changes play the most crucial role in a bubble's growth in size.