Page 1: Probe and Ponder
Q1: Why is it possible to pile up stones or sand, but not a liquid like water? Answer: Stones and sand grains are solids. Each individual grain has a fixed shape and strong forces holding its own particles together. Water is a liquid; its particles are free to flow and slide past each other, so it cannot maintain a pile and flows away due to gravity.
Q2: Why does water take the shape of folded hands but lose that shape when released? Answer: Water is a liquid. Its particles have weaker attractive forces than solids, allowing them to flow and adapt to the shape of any “container” (like your folded hands). When the support (hands) is removed, gravity pulls the water down, and since it has no fixed shape, it flows away.
Q3: We cannot see air, so how does it add weight to an inflated balloon? Answer: Even though air is invisible, it is made of matter (particles). These particles have mass. When you inflate a balloon, you force billions of air particles into it. The combined mass of these particles adds weight to the balloon.
Q4: Is the air we breathe today the same that existed thousands of years ago? Answer: The matter (atoms and molecules) is largely recycled through cycles (like the carbon cycle and water cycle), but the composition has changed slightly due to pollution and geological changes. However, the fundamental particle nature remains the same.