Contents 1
1．What Caused the Tower of Pisa to Lean ？ 1
2．Was America Discovered Before Columbus ？ 5
3．Does the Whole World Have Time Zones ？ 8
4．How Does a Refrigerator Produce Cold ？ 12
5．What Makes anAirplane Stay up ？ 16
6．What Is Radar ？ 20
7．How Did Our System of Counting Begin ？ 24
8．Who Discovered Electricity ？ 28
9．Who Built the First Lighthouse ？ 31
10．Who Discovered the Atom ？ 35
11．Who Invented the Airplane ？ 39
12．How Big Is the Universe ？ 42
13．What Is the Milky Way ？ 45
14．What Are Falling Stars ？ 48
15．Where Does the Wind Come From ？ 52
16．What Is Fog ？ 56
17．What Is Dew？ 60
18．Why Do Snowflakes Have Six Sides ？ 64
19．Why Does Frost Form on Windows ？ 68
20．How Does Water Change to Ice ？ 71
21．What Is a Rainbow？ 75
22．What Is Light ？ 79
23．How Fast Does Sound Travel ？ 82
24．What Is Energy ？ 85
25．What Is Heat ？ 89
26．What Is Friction ？ 93
27．Why Does Iron Get Rusty ？ 96
28．What Is an Alloy ？ 99
29．What Is Petroleum ？ 103
30．Why Do We Get Tired ？ 107
31．What Happens When We Sleep ？ 111
32．What Causes Our Dreams ？ 114
33．Why Do We Laugh ？ 118
34．What Is Cancer ？ 121
35．Can Animals See in Color ？ 125
36．Why Does a Male Bird Have Brighter Colors Than the Female ？ 128
37．How Do Birds Find Their Way Home？ 131
38．How Do Fish Breathe ？ 135
39．Can Any Fish Live out ofWater ？ 138
40．Can a Porpoise Talk ？ 142
Glossary 145