Consider a bicycle pump. Why does the air inside the pump cylinder get noticeably warmer when you rapidly push the plunger down, even without any external heat source?

8 views 1 helpful Updated Jul 27, 2026
Appears in Class 8th
Solution ✔ Verified
  • AFriction between the plunger and the cylinder walls generates heat.
  • BThe rapid compression of air increases the frequency and force of molecular collisions, which translates to a rise in temperature.
  • CThe pump is designed to convert kinetic energy directly into thermal energy.
  • DAir molecules absorb heat from the surrounding environment during compression.
Explanation

When you rapidly push the plunger down, you are doing work on the air inside, causing it to be compressed into a smaller volume. This compression forces the air molecules closer together, increasing the frequency and force of their collisions with each other and the container walls. This increased molecular kinetic energy manifests as a noticeable rise in temperature.

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