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A metal bar is heated. Its mass stays the same but the bar gets slightly longer. What happens to its density?
AIt becomes larger
BIt stays the same
CIt becomes zero
DIt becomes smaller
Answer & Solution
Correct answer: D. It becomes smaller
1. Heating gives the particles more energy so they move further apart.
2. The number of particles does not change, so the mass in grams stays the same.
3. The bar takes up more space, so its volume in millilitres goes up.
4. Density is mass divided by volume, so a larger volume with the same mass lowers it.
5. The density therefore becomes smaller when the bar is heated.
6. It cannot stay the same, because only one of the two quantities has changed.
7. It cannot reach zero, because the bar still has mass.
_Source: Siyavula Natural Sciences Grade 8 (CC BY 4.0), Expansion and contraction of materials_