A metal rim expands on heating due to thermal expansion, a property of materials where they increase in size when temperature rises.
Concept Explanation:
- Metals are made of atoms arranged in a lattice.
- When heated, atoms gain kinetic energy and vibrate more vigorously.
- This increased vibration causes the average distance between atoms to increase, leading to expansion.
Key Principle:
- Expansion occurs uniformly in all directions.
- Even the hole (inner diameter) of a metal rim expands, not contracts.
Mathematical Expression:
For linear expansion:
ΔL = α L ΔT
Where:
- ΔL = change in length
- α = coefficient of thermal expansion
- ΔT = change in temperature
Practical Application:
- Metal rims are heated to fit onto wheels or shafts easily
- On cooling, they contract and fit tightly
Conclusion:
A metal rim expands on heating because increased atomic vibrations push atoms farther apart, causing an overall increase in dimensions.