Probe and Ponder Solutions

Page 1: Probe and Ponder

These questions are designed to spark curiosity. While they don’t have single “exam-style” answers, here are the scientific explanations behind them.

1. Why is one side of a puri thinner than the other?

Scientific Explanation: When a rolled dough disk is dropped into hot oil, it submerges. The bottom side contacts the hot oil first.

1. Heat Transfer: The bottom layer gets cooked and stiffens almost immediately.
2. Steam Generation: Water in the dough turns to steam.
3. Expansion: The steam pushes upward. Since the bottom is already slightly stiff, the steam expands the upper layer, which is still soft and elastic.
4. Result: The upper layer stretches significantly more than the bottom layer, becoming thinner as it expands like a balloon.

2. Are there more grains of sand on all the beaches and deserts of the world, or more stars in our galaxy?

Scientific Estimate: This is a classic “Fermi Problem” (an estimation problem).

• Grains of Sand: Scientists estimate there are roughly $7.5 \times 10^{18}$ (7.5 quintillion) grains of sand on Earth.
• Stars in the Universe: There are approximately $10^{11}$ to $10^{12}$ stars in our galaxy (Milky Way), and there are roughly $2 \times 10^{12}$ galaxies in the observable universe. The total stars are estimated around $10^{22}$ to $10^{24}$.

Answer: There are far more stars in the Universe than grains of sand on Earth. However, if we restrict it just to our galaxy (The Milky Way), grains of sand might outnumber the stars.

3. Why has nature created such a vast variety of plants and animals?

Scientific Concept: Evolution and Adaptation. Nature has a vast variety because environments vary (deserts, oceans, forests).

• Living things possess variations (differences).
• Those with traits best suited to their specific environment survive and reproduce.
• Over millions of years, this leads to Biodiversity, ensuring life can survive in almost any condition on Earth.