Did you know that a ceramic mug can tolerate a warm drink one day yet crack when it experiences a sufficiently sudden change in temperature? A Secondary 1 student may think the ceramic simply melted, or that cold water somehow cuts through the mug. I ask a better question: What happens when one part of a brittle solid changes temperature faster than another part, so the regions try to expand or contract by different amounts? That is the beginning of the explanation of *thermal shock*.
For families looking for a Secondary 1 Chemistry Tutor Hougang, the quick answer is that rapid, uneven temperature changes can create mechanical stresses inside ceramic material because different regions expand or contract at different times. If the stress at a flaw or weak region becomes large enough, a crack can form or grow. Many ceramics resist high temperatures in suitable steady conditions yet can fracture under an abrupt temperature gradient. The effect depends on composition, thickness, manufacturing flaws, glaze and design. It does not mean every ceramic mug must crack when any warm drink is added.
This example brings together the properties of materials, thermal energy transfer, expansion and contraction, particles, measurement and careful conditional language. Singapore Secondary 1 pupils ordinarily study Chemistry-related foundations within integrated lower-secondary Science rather than a standalone national Pure Chemistry examination. G1, G2 and G3 courses differ in depth and sequence; fracture mechanics and formulas are enrichment when beyond the student’s class. We will teach the physical cause first, then build to worked cases, fair tests, safe interpretation and a small-group tutorial plan. Never deliberately shock, heat or break ceramic or glass objects to demonstrate the effect.
1. Observe a crack without pretending to see stress
The visible outcome may be a narrow crack, a shattered mug or a glazed surface with fine lines. The observation itself does not identify every internal stress or the precise history of the material.
A student should first describe the defect, then use the provided temperature conditions to support a thermal-shock explanation. Without that history, impact damage or an earlier flaw could also be relevant.
2. What ceramic means
Ceramics are inorganic, non-metallic materials often formed and processed at high temperatures. Many common mugs are made from clay-based ceramic bodies whose constituents transform during firing.
Ceramic does not mean one pure element or one universal compound. Porcelain, stoneware and earthenware differ in composition and microstructure, affecting strength and thermal behaviour.
3. Ceramic mugs are manufactured materials
A typical mug contains a body formed from mineral raw materials and may have a glassy glaze on its surface. The firing process changes the material’s microstructure and creates its final shape and properties.
The overall product can contain multiple phases, pores and interfaces. We should not describe it as one flawless single crystal merely because the outside looks smooth.
4. What high-temperature resistance means
A suitable ceramic material may withstand exposure to relatively high temperatures without melting or decomposing under its intended use conditions. That property is not identical to its resistance against sudden temperature gradients.
A child who says ‘it was fired in a hot kiln, so it can never crack from hot water’ has confused manufacturing temperature with thermal-shock resistance in a finished object.
5. The main idea: thermal expansion
Many materials change dimensions as their temperature changes. Heating generally causes expansion over relevant ranges, while cooling tends to cause contraction. The amount depends on material and temperature interval.
A simple drawing can show a solid becoming slightly longer after uniform heating. The actual dimensional change in ceramic objects is often small, but even small constrained changes can produce important stresses.
6. Uniform heating is not the same as uneven heating
If a mug warms relatively evenly, its regions can expand more compatibly. If the inside heats quickly while the outside remains cooler, the different regions tend to change size by different amounts.
That mismatch can generate internal stresses. The problem is not simply that the material was hot, but that a temperature gradient developed and the body could not accommodate it without excessive stress.
7. What a temperature gradient is
A temperature gradient is a change in temperature from one position to another. A mug wall can be warmer on its inner face than on its outer face during rapid heating, depending on thickness and heat-transfer conditions.
The student’s diagram should label the warm and cool regions rather than give one identical temperature to every part of the wall. The gradient is central to the thermal-shock mechanism.
8. How heat moves through a wall
Thermal energy transfers through the ceramic wall by conduction. The rate depends on material conductivity, thickness, geometry and the temperature difference. The outer surface may not warm as rapidly as the inner surface.
A more conductive material can redistribute heat more quickly under suitable conditions, potentially reducing some temperature gradients. But fracture resistance also depends on strength, expansion and flaws, so conductivity alone is not a universal prediction.
9. Why the inside and outside can disagree mechanically
Suppose the inner layer is suddenly heated and tries to expand while the outer layer remains cooler. Because they are joined as one solid, the layers cannot expand independently without producing deformation and stress.
The ceramic is not filled with little springs that have been pulled by hand. The constraint comes from the continuous solid structure, which connects regions at different thermal states.
10. What stress means in materials Science
Stress describes internal force per unit area within a material. Thermal expansion mismatch can produce stress even if no person is visibly pulling on the mug.
The detailed stress distribution depends on geometry and which regions are heated or cooled. A first-year learner can understand the qualitative mismatch without calculating a tensor or solving elasticity equations.
11. Why ceramics are often brittle
Many ceramics can sustain substantial compressive forces but fail relatively suddenly when tensile stresses become too high, especially near pre-existing flaws. They do not usually show the large plastic deformation common in many metals.
The University of New South Wales materials-science tutorial explains why flaws can concentrate stress and why thermal shock can fracture ceramics. This is the structural explanation behind an everyday crack.
12. Tensile and compressive stress
Tension tends to pull a region apart, while compression tends to squeeze it. A thermal gradient may create both in different parts of an object, depending on geometry and the direction of heating or cooling.
Cracks often propagate from regions experiencing excessive tensile stress. The pupil should not assume the same surface is always in tension in every thermal-shock arrangement.
13. Why a tiny flaw can matter
Small pores, scratches or pre-existing cracks can act as stress concentrators. Local stresses near a flaw can exceed those suggested by an average calculation over the whole mug.
A smooth-looking surface does not guarantee the ceramic is microscopically flawless. This is why two apparently similar products may respond differently under the same thermal conditions.
14. How a crack can grow
When local tensile stress is sufficient, an existing crack may extend. As the crack propagates, the object can lose mechanical integrity and sometimes separate suddenly.
The crack’s movement is a mechanical fracture event, not necessarily a chemical reaction converting ceramic into a new element. It is a consequence of stress and structural weakness.
15. Sudden cooling can also be harmful
Thermal shock is not limited to pouring hot liquid into a cold mug. Rapidly cooling a hot ceramic surface can also create large temperature differences between regions.
The stress direction and location may differ from rapid heating, but the underlying issue is again uneven expansion or contraction. Never test this by plunging hot crockery into cold water.
16. Why the outer surface might contract first
If a hot ceramic item is cooled sharply from the outside, its surface may contract more quickly than the warmer interior. The connected regions constrain one another, potentially creating high thermal stress.
The explanation should not claim that cold is a separate material flowing into the cracks. Thermal energy leaves the hotter regions, producing spatially uneven temperature change.
17. A mug is not a perfect uniform cylinder
Handles, bases, rims, glazes and changes in wall thickness influence how heat flows and how stress develops. The junction between a handle and the body can behave differently from the middle of a wall.
A detailed fracture diagnosis would need more information than a generic drawing. For Secondary 1, recognise that shape and thickness matter alongside ceramic composition.
18. Why a thick wall can have larger gradients
Under some rapid heating conditions, a thicker wall can maintain a larger temperature difference between its inner and outer faces than a thinner wall of the same material. However, thickness also affects mechanical strength and heat capacity.
Thus ‘thicker mug always safer from thermal shock’ is not a universal rule. Design has multiple interacting factors, and the correct answer should follow the stated conditions.
19. Why the handle may crack at a joint
A handle is joined to the mug body and may have different geometry or processing stresses. When the object experiences mechanical and thermal loading, stress concentrations near joins can be important.
The handle falling off is not sufficient evidence that thermal shock was the cause. Manufacturing defects, accidental impact and earlier damage can also matter.
20. What is a ceramic glaze?
A glaze is a surface layer, often glassy, applied to ceramics for useful appearance and performance. It is not necessarily the same composition or thermal expansion behaviour as the body underneath.
A coating can be strong and glossy while experiencing different stresses from the substrate during temperature changes. That makes the relationship between glaze and body a separate materials-design problem.
21. Why glaze can form fine cracks
Crazing describes fine networks of cracks in a glaze, which can arise when stresses develop due to expansion mismatch between glaze and body or other factors over time. It is not automatically identical to a through-body fracture.
A student should distinguish a surface pattern from a crack through the entire ceramic wall. One photograph might not reveal the extent of damage, so a product should not be declared safe from appearance alone.
22. Glaze expansion mismatch
If a glaze and ceramic body expand differently, heating or cooling can create stress at their interface. Manufacturers select compatible materials and firing conditions to manage this.
The problem is structurally related to thermal shock but may involve specific residual stresses from processing. The student’s main lesson is that two connected materials cannot always change size independently.
23. Thermal shock versus impact damage
An object can crack from being dropped, struck or thermally shocked. The visible fracture pattern and history may provide clues, but no generic photograph uniquely proves the mechanism.
A good exam answer uses the conditions explicitly supplied. If the question states a sudden temperature difference and no impact, explain thermal stress. If the history is unknown, qualify the inference.
24. Why glass can also break from temperature changes
Many glasses behave as brittle materials and can fracture under uneven thermal expansion. Although glass may be amorphous rather than crystalline, the broad thermal-stress problem is related.
This provides a useful comparison without claiming that every glass and ceramic shares one formula or identical thermal-shock resistance.
25. Why borosilicate glass often resists thermal shock better
Borosilicate glass is engineered with comparatively low thermal expansion for many uses, helping reduce stresses generated by a given temperature gradient. Its performance still depends on shape, flaws and intended operating conditions.
The phrase ‘heat-resistant glass’ is not a licence to subject every product to unlimited temperature changes. Always follow the manufacturer’s use instructions.
26. Why metal can deform differently
Many metals are more ductile and can accommodate some deformation without brittle fracture in situations where a ceramic would crack. They also often conduct thermal energy differently.
It is still wrong to say metals can never crack or suffer thermal stress. Material selection requires specifying composition, geometry and operating conditions.
27. How polymer cups differ
Some polymers can deform substantially without immediately fracturing, but their temperature limits, thermal expansion and chemical compatibility differ from ceramic materials.
A polymer cup may soften or deform at a temperature that a ceramic mug tolerates, illustrating why ‘does not shatter’ is not the same as ‘best material for every hot drink’.
28. Does the ceramic melt when it cracks?
No. Ordinary thermal-shock cracking can occur at temperatures far below the material’s melting range. The failure arises from mechanical stress due to uneven heating or cooling.
A student who states that hot water melted the mug has selected the wrong mechanism. Temperature gradients and brittle fracture are the key ideas.
29. Does cracking create a new chemical compound?
A fracture changes the object’s mechanical integrity and exposes new surfaces, but does not necessarily transform the ceramic into an entirely different chemical substance.
Manufacture and some environmental exposures can involve chemical changes; the act of cracking under thermal stress is primarily a mechanical event. The question must specify which process is being classified.
30. What does thermal conductivity contribute?
Thermal conductivity affects how quickly energy redistributes within a material. A relatively low conductivity can allow a temperature gradient to persist during abrupt exposure.
However, it does not determine fracture on its own. Thermal expansion coefficient, stiffness, tensile strength, flaws and geometry all influence the response.
31. Coefficient of thermal expansion
This material property describes how dimensions tend to change with temperature over a specified range. Different ceramics and glasses have different coefficients of thermal expansion.
For a new learner, the qualitative idea is enough: more expansion mismatch can mean more potential stress under constrained conditions. The exact formula is extension content when the school has introduced it.
32. A simplified length calculation
If a fictional 10.0 cm strip with constant expansion coefficient 5 × 10⁻⁶ K⁻¹ is uniformly heated by 100 K, the linear expansion estimate is ΔL = αLΔT = 0.005 cm.
The small size illustrates why thermal stresses can matter despite tiny visible dimensional changes. This formula is enrichment and should not be required unless the relevant Physics or Science content has been taught.
33. Why a small expansion can break a brittle solid
Even a microscopic mismatch between strongly connected regions can produce large internal forces because neither region is free to change length independently. Brittle materials can have limited ability to redistribute such stress plastically.
The child should not assume that a change too small to see is too small to matter. Science frequently connects microscopic causes with large visible outcomes.
34. A fictional temperature-gradient table
A teacher provides inner-wall temperatures of 30, 50 and 70 °C and corresponding outer-wall temperatures of 28, 35 and 45 °C at three times. The differences are 2, 15 and 25 °C.
The increasing gradient suggests growing mismatch during the stated heating stage. It does not by itself prove fracture will occur; the material’s resistance and flaws are also needed.
35. Calculate a wall-temperature difference
Question: The inner surface is 75 °C and the outer surface is 48 °C. What is the difference? Answer: 27 °C.
The subtraction is a measurement of thermal contrast, not the amount of stress or crack length. Do not invent a direct stress value without the appropriate material data and model.
36. Why the same hot drink may behave differently in two mugs
Two mugs may have different compositions, glazes, thicknesses, shapes and histories of damage. Even if filled with liquid at the same temperature, the resulting stress and fracture resistance can differ.
This is why one kitchen observation does not provide a universal ceramic temperature limit. Product specifications and condition matter for actual use.
37. What a fair comparison would require
A proper materials experiment would specify sample composition and geometry, initial temperature, change in thermal boundary conditions and measured outcome. A class can examine published results or a fictional dataset instead of breaking crockery.
If one sample is cracked in advance while another is new, we cannot attribute different results solely to material type. The controlled variables must match the research question.
38. The independent variable depends on the aim
If the school investigates how temperature-change rate affects damage in identical model samples, the rate is the independent variable. If comparing ceramic types, the material identity becomes the main factor.
The dependent measure could be whether damage occurred or a quantitative crack indicator. The experimental design determines the variable labels; they are not fixed by which word appears on a graph.
39. Why real cups should not be shock-tested at home
Abrupt heating or cooling can cause hot-liquid spills and sharp fragments. Children should never pour boiling water into a frozen mug, plunge hot ceramic into icy water or intentionally induce fracture.
These actions add hazards without improving the conceptual explanation. A safe diagram and teacher-supplied measurements are sufficient to teach thermal gradients and brittleness.
40. What a cracked mug means for safe use
A mug showing cracks, damage or leakage may be unsuitable for normal food or drink use. Do not treat a Chemistry lesson as evidence that a cracked item is safe because the fracture is ‘only physical’.
Practical safety decisions require condition, material and manufacturer guidance. The scientific cause of a crack and the appropriate response to a damaged object are related but different questions.
41. Does a glaze colour reveal strength?
A glossy blue or white glaze does not uniquely identify the ceramic body’s fracture strength or thermal expansion coefficient. Different compositions and processing can produce similar appearance.
A student should avoid using decoration or colour as a substitute for measurements of mechanical and thermal properties.
42. A comparison with heat-sensitive mugs
A thermochromic novelty mug changes visible colour because of temperature-sensitive pigment chemistry in its coating. A ceramic mug can crack because of constrained thermal expansion and brittle fracture.
The same stimulus—temperature change—can produce entirely different outcomes and mechanisms. Read the heat-sensitive mug guide to avoid confusing optical switching with mechanical fracture.
43. A comparison with vacuum flasks
A vacuum flask slows thermal energy transfer through its engineered layers. A ceramic mug under thermal shock can develop large gradients because of rapid heating or cooling and its material properties.
Both involve heat transfer and material selection, but the useful question differs. The vacuum flask guide focuses on insulation, not fracture mechanics.
44. Worked explain question
Question: ‘Explain why sudden heating can crack some ceramic mugs.’ A good answer says the inner and outer parts warm at different rates and tend to expand by different amounts. The resulting stress can grow cracks in a brittle material.
A weak answer says ‘the mug melts instantly’. Another says ‘heat destroys ceramic atoms’. Neither identifies temperature gradients and stress.
45. Worked predict question
Question: ‘A mug has a microscopic crack. Might it be more vulnerable to thermal stress?’ Yes, because the flaw can concentrate stress, although the actual outcome depends on conditions.
The student should not assign one exact fracture temperature from a diagram alone. Material strength, geometry and gradient matter.
46. Worked comparison question
Question: ‘Compare rapid uniform heating with strongly uneven heating of the same ceramic body.’ Uneven heating can generate larger internal expansion mismatches and therefore greater thermal stresses under appropriate conditions.
This is a conditional comparison, not a guarantee that every uniform temperature change is harmless or every small gradient cracks the object.
47. Worked numerical question
Question: The inner wall reads 80 °C and the outer reads 55 °C. Find the difference. Answer: 25 °C.
The correct unit is °C for a difference between two temperature readings. This number describes the gradient across the wall in the simplified example, not a computed stress.
48. G1 learning route
For G1, use a simple mug-wall diagram with one warm region and one cooler region. Explain that different parts try to expand by different amounts and the brittle mug may crack.
Follow the MOE G1 lower-secondary Science syllabus and current class content before introducing expansion coefficients.
49. G2 learning route
A G2 learner can connect heat conduction, uneven expansion and the tendency of brittle materials to fracture. A changed example involving rapid cooling should test whether the model transfers.
Use the MOE G2/G3 lower-secondary Science syllabus and the school’s actual teaching sequence.
50. G3 learning route
A secure G3 learner can discuss thermal expansion coefficient, conductivity, flaws and stress concentration. They can also explain why the same measured gradient does not uniquely predict failure across different ceramics.
The full mechanics equations are enrichment if not in the student’s school course. The aim is understanding how several physical properties work together.
51. A 90-minute small-group lesson
Minutes 0–10: Diagnose what pupils think a crack means. 10–25: Teach expansion and contraction with diagrams. 25–40: Explain gradients and constrained movement. 40–55: Introduce brittleness and flaws.
55–70: Interpret fictional inner/outer temperature readings. 70–80: Correct the false rule ‘kiln-fired mugs cannot crack’. 80–90: Each learner answers an unfamiliar rapid-heating or rapid-cooling case independently.
52. What parents should ask a tutor
One child may confuse cracking with melting; another understands thermal expansion but ignores the gradient; a third can explain the cause but misreads the temperature table.
Those are different missing links. A tutor should repair the precise one and test a changed problem. Hougang and Kovan families should verify the actual lesson venue, subject level, class size and availability rather than assume a local page guarantees a teaching slot.
53. Frequently asked questions
Why can a ceramic mug crack when heated suddenly? Uneven thermal expansion can create stress that exceeds the strength of a brittle region. Can rapid cooling also matter? Yes. Does the mug melt? Not in the ordinary thermal-shock explanation.
Can two mugs respond differently? Yes. Does a fine glaze crack mean the whole body fractured? Not necessarily. Is it safe to test at home? No—use diagrams and supplied data.
54. Authoritative reference
The University of New South Wales School of Materials Science and Engineering: Ceramics Properties and Thermal Shock explains brittle fracture, thermal expansion and rapid temperature-change damage.
This supports the mechanism but does not specify the safe temperature range of an unknown household mug. A relevant product’s manufacturer and condition determine appropriate use.
55. Continue through the Hougang Chemistry library
Compare Why a Vacuum Flask Keeps Drinks Hot and Cold, Heat versus Temperature and Why Heat-Sensitive Mugs Change Colour.
Return to the Hougang Chemistry Tutor Library. The key question is ‘Which regions are hotter or colder, how do they want to change shape, and what prevents them from moving independently?’
28 Worked Questions and Transfer Checks
Q1. The main mechanism
What is thermal shock? Answer: Stress or damage associated with rapid temperature changes and resulting gradients.
It is not another name for melting.
Q2. Expansion
What generally happens to dimensions when many solids heat? Answer: They expand slightly.
Actual response depends on material and temperature range.
Q3. Cooling
What can happen as a solid cools? Answer: It may contract.
Abrupt nonuniform contraction can create stress.
Q4. Gradient
What is a temperature gradient? Answer: A difference in temperature between positions.
The wall need not be uniformly heated.
Q5. Mug wall
Why can a hot interior and cool exterior cause problems? Answer: They try to expand differently while connected.
Internal stress can result.
Q6. Brittleness
Why are ceramics often vulnerable? Answer: They may fracture under excessive tensile stress without much plastic deformation.
Defects can intensify that stress.
Q7. A pre-existing flaw
Can a small scratch affect crack growth? Answer: Yes.
A flaw may concentrate stress.
Q8. Uniform versus uneven
Which can generate stronger thermal mismatch under suitable conditions? Answer: Highly uneven heating.
The answer depends on geometry and material.
Q9. Rapid cooling
Can cooling a hot ceramic surface too rapidly crack it? Answer: Yes.
A sudden external contraction can stress the connected structure.
Q10. Melting claim
Does a cracked ceramic mug necessarily melt? Answer: No.
Fracture is a mechanical event, not necessarily a change of state.
Q11. Glaze versus body
Is glaze cracking always the same as a complete through-body crack? Answer: No.
Different layers may experience different stresses.
Q12. A glass comparison
Can some glass also fracture from thermal shock? Answer: Yes.
Material composition and thermal expansion matter.
Q13. Borosilicate
Why can some borosilicate products resist thermal shock well? Answer: Their relatively low thermal expansion reduces mismatch stresses.
Follow product specifications for actual safe use.
Q14. A temperature difference
Inner wall 90 °C, outer wall 60 °C. What is the difference? Answer: 30 °C.
That is not itself a numerical stress value.
Q15. A second difference
Inner wall 45 °C, outer wall 40 °C. Difference? Answer: 5 °C.
The relative gradient is smaller than in the preceding example.
Q16. Independent variable
If varying heating rate, what is the independent factor? Answer: Rate of temperature change.
The dependent outcome might be measured damage.
Q17. Controlled material
Why use comparable ceramic samples? Answer: To avoid composition and flaw differences confounding the heating-rate comparison.
A fair test changes the intended factor.
Q18. A strength test
Does visible colour identify a mug’s tensile strength? Answer: No.
Mechanical testing and composition matter.
Q19. Two mugs
Can two mugs with identical colour behave differently? Answer: Yes.
Glaze, body, geometry and flaws may differ.
Q20. A thick wall
Is thicker automatically safer from thermal shock? Answer: No.
Thickness affects both heat gradients and mechanical design.
Q21. Safety
Should a pupil deliberately plunge a hot mug into ice water? Answer: No.
Shattering, sharp fragments and burns are hazards.
Q22. A crack
Should a cracked food-contact mug automatically be considered safe? Answer: No.
Follow manufacturer and practical food-safety guidance.
Q23. G1 checkpoint
Draw warm and cool parts of a wall and explain the mismatch.
Use a short causal story.
Q24. G2 checkpoint
Connect conduction, expansion and brittle fracture in a labelled diagram.
The model should include a temperature difference.
Q25. G3 checkpoint
Identify expansion coefficient, conductivity and flaws as separate factors.
One property alone does not decide the outcome.
Q26. Contrast with a mug’s colour change
Is a thermochromic mug changing colour the same as a body cracking? Answer: No.
One is an optical response; the other can be mechanical fracture.
Q27. A parent question
Why can a mug tolerate a stable hot environment but be vulnerable to a rapid change? Answer: The sudden difference creates stress before temperature equalises.
This is the core of thermal shock.
Q28. Final transfer
A brittle tile is heated unevenly and develops a crack. Could thermal stress be a plausible mechanism? Answer: Yes, subject to the specified conditions.
A correct pupil recognises the transferable cause without claiming that every crack was thermally produced.
Extended Cases: Faults, Temperature History and Material Selection
29. The unseen flaw case
Two ceramic mugs look identical, but one contains a very small manufacturing flaw. When both undergo the same abrupt temperature change, the damaged piece may be more susceptible to crack growth because the flaw concentrates local stress.
That does not guarantee it will be the one that fails. Fracture depends on the exact location, size and orientation of flaws and the stress field. A student should distinguish a plausible risk factor from an absolute prediction.
30. The warm-rim versus cool-base question
Imagine a mug whose rim becomes warm while its thick base remains relatively cool. A temperature gradient exists within the object, so different regions can tend to expand differently. The complicated geometry can affect the resulting stress.
This case tests whether the child understands that the thermal-shock mechanism is not limited to a simple flat wall. They should label the hot and cool regions and consider how connected material constrains motion.
31. Why a manufacturer may choose one ceramic over another
A product designer might compare thermal expansion, mechanical strength, thermal conductivity, glaze compatibility, cost and ability to survive expected use. A material that performs best on one measure may be weaker on another.
The correct engineering decision is made for the intended temperature profile, shape and lifetime, not simply by choosing the most expensive or thickest material. This is the same structure–property reasoning that supports other Chemistry and Science topics.
32. How temperature equalisation changes the situation
If a ceramic object is heated slowly enough for its regions to remain comparatively similar in temperature, the thermal mismatch may be smaller than after a sudden large change. That can reduce one source of stress under suitable conditions.
The general trend does not certify any particular mug as safe for arbitrary heating. The material may have other limitations, and manufacturer instructions remain the appropriate guide for real products.
33. A question about thermal-shock resistance
One ceramic composition expands less than another for the same uniform temperature change. Does the lower-expansion material always survive every thermal shock? Not necessarily; toughness, conductivity, defects, geometry and actual loading also contribute.
This is an excellent evidence question because a single property does not fully determine the performance of a multi-factor material. The child should identify which additional information a fair comparison needs.
34. Return to the first-principles explanation
A student can finish with three sentences: ‘Thermal energy enters or leaves different regions at different rates. Those regions tend to change dimensions differently while connected. If the resulting stress exceeds local fracture resistance, a crack can grow.’
The explanation is more valuable than memorising the word thermal shock. It can transfer to glassware, tiles and other brittle materials while staying conditional on the actual conditions.