Question 1

Why does a hole expand when the surrounding solid is heated?

Accepted Answer

A hole is empty space bounded by the material, not a separate object. As the surrounding solid expands, its boundary moves outward, so the hole's diameter increases as though the hole were filled with the same material.

Question 2

Why does the brass ball jam in the iron ring at 200 °C?

Accepted Answer

From 20 °C to 200 °C, the brass ball diameter increases by 0.0684 mm, while the iron hole increases by about 0.0432 mm. Their differential diameter growth is therefore about 0.0252 mm, which exceeds the initial 0.0200 mm clearance by about 0.0052 mm; that 0.0052 mm is the resulting interference.

Question 3

Does the ball jam immediately above 20 °C?

Accepted Answer

No. The clearance becomes smaller gradually. With the stated dimensions and constant coefficients, the two diameters become equal at about 163 °C; the ball jams at higher temperatures.

Question 4

Why is the visual enlargement in the 3D model labeled?

Accepted Answer

The actual millimetre changes are much smaller than the 20 mm body. The model enlarges the thermal changes and initial radial clearance consistently by a factor of 12 for visibility, so the visual fit threshold remains near 163 °C; all displayed diameters and clearances use the actual textbook values.

Question 5

Is thermal expansion always reversible?

Accepted Answer

Within the constant-coefficient linear model it is reversible when cooling and reheating do not cause permanent deformation. Real materials can also undergo permanent changes at sufficiently high temperatures or after repeated cycling.

Thermal Expansion Lab — Why the Ball Jams the Ring

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Practice