Which indicates that the clump in a lava lamp is moving downward rather than upward?

Which indicates that the clump in a lava lamp is moving downward rather than upward?

• A. It is less dense than the surrounding liquid.
• B. Its molecules are losing kinetic energy.
• C. Its molecules begin to slow down before they become faster.
• D. Its temperature increases before it decreases again.

Answer: (D)

Movement in a lava lamp is driven by changes in density caused by heating and cooling. A blob rises when it becomes less dense than the surrounding liquid (it’s warmer and lighter), and it sinks when it cools and becomes denser. The statement that the blob’s temperature increases first and then decreases again signals this heating then cooling cycle. After heating, the blob cools and its density increases, causing it to sink. This pattern—warming followed by cooling leading to sinking—is what indicates downward movement. The other cues don’t directly tie to the density change needed for sinking: being less dense would push the blob upward; simply losing kinetic energy describes cooling but doesn’t specify relation to the surrounding liquid’s density; a slowing then speeding in the molecules doesn’t address density changes; and temperature increasing before decreasing points to the cooling phase that results in sinking.

Movement in a lava lamp is driven by changes in density caused by heating and cooling. A blob rises when it becomes less dense than the surrounding liquid (it’s warmer and lighter), and it sinks when it cools and becomes denser.

The statement that the blob’s temperature increases first and then decreases again signals this heating then cooling cycle. After heating, the blob cools and its density increases, causing it to sink. This pattern—warming followed by cooling leading to sinking—is what indicates downward movement. The other cues don’t directly tie to the density change needed for sinking: being less dense would push the blob upward; simply losing kinetic energy describes cooling but doesn’t specify relation to the surrounding liquid’s density; a slowing then speeding in the molecules doesn’t address density changes; and temperature increasing before decreasing points to the cooling phase that results in sinking.