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Why does a steel spring snap back into shape while a lump of clay simply stays bent? Why is a raindrop round rather than any other shape? Why does honey crawl out of a jar while water rushes out?
Three properties of matter answer all of it. Elasticity is a solid's ability to return to its original shape once the load is removed. Surface tension is the pull along a liquid's surface that makes it behave like a stretched skin. Viscosity is a fluid's internal friction — its reluctance to flow.
General science papers return to these three every year, and almost always through everyday examples rather than heavy calculation: insects standing on pond water, oil rising in a lamp wick, a parachute falling at a steady speed. Get the definitions and the two or three formulas straight, and the examples answer themselves.
1. Which of the following is the most elastic?
2. The SI unit of surface tension is:
3. Young's modulus of a material is the ratio of:
4. A falling raindrop takes a spherical shape mainly because of:
5. When the temperature of a liquid is increased, its surface tension:
6. With a rise in temperature, the viscosity of a gas:
7. Water rises in a narrow glass tube dipped in it mainly because:
8. A small ball dropped into a tall jar of oil soon starts falling with a constant velocity because: