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Changes Around Us: Physical and Chemical

Slow changes in rocks

Rock and soil slide down a hill in a landslide. The landslide leaves a pile of stones. What made them?

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The idea

One big rock.
Step 1 of 4
  1. One big rock.
  2. A crack opens.
  3. It breaks into smaller pieces.
  4. Over time it becomes sand and small stones.

Big rocks break into stones, very slowly.

Weathering is the slow breaking or changing of rocks. It forms soil.

  • Physical: frozen water in cracks and tree roots split rocks. Heat and cold split them too.
  • Chemical: water can react with a rock. Black rock with iron can form a red layer of iron oxide. Iron oxide is iron joined with oxygen.

Erosion is wind or flowing water carrying broken rock away. It is a physical change.

The rule

Rocks break in physical changes. Some rocks change into new substances. Most of these changes are slow.

These changes can take thousands of years. They are not undone.

Jump to lesson

This track

  1. 0 Start here
  2. 1 Fold it, cut it, crumple it
  3. 2 Ice, water and steam are one substance
  4. 3 Dissolving is not disappearing
  5. 4 Some of these will not go back
  6. 5 Checkpoint: changes that make nothing new
  7. 6 A test for something new
  8. 7 Five signs, and what each one is worth
  9. 8 One candle, two changes at once
  10. 9 Two questions, not one
  11. 10 Slow changes in rocks
  12. 11 Checkpoint: new substances and the two questions
  13. 12 Burning needs air
  14. 13 The fire triangle
  15. 14 A change written in words
  16. 15 Useful and harmful changes
  17. 16 Checkpoint: burning, equations and useful changes
  18. 17 The big picture
  19. 18 Track quiz

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