People for long time have dreamed of a flying machine that could rise from the ground right up. Leonardo Da Vinci around year 1500, made a drawing of giant helicopter,…
A heliograph can be seen up to 30 miles (48 kilometers) away on a clear day without a telescope. The modern heliograph is mounted on a tripod, like a camera.
Throughout history, armies and navies have sent messages across battlefields. Simple orders like “Advance” or “Retreat” could be given by bugle calls or cannon-fire. But sending reports of the battle…
Who was Marco Polo? Marco Polo was the first European to travel to Asia and tell his story. His book, "The Travels of Marco Polo" is the most famous travel…
Why is a day on earth 24 hours? The day lasts 24 hours just because the humans wanted to share it in such manner. There is nothing in nature that…
Do you live in a place where the water is "hard"? It is easy to tell if you do, because a chalky layer, or scale, will usually build up inside your…
We sometimes call valuable metals, such as platinum and gold, precious metals. Platinum is the most valuable metal in the world. It is called a catalyst because it produces a…
The weight of this air pressing down all around the earth produces air pressure. It is probably moving enough to make the branches on the trees sway slightly.
What is an airfoil? When an airfoil moves through the air, it produces lift because the force of the air pushing down on its top surface is less than the…
About one-fifth of the air is oxygen. Human beings and other animals would not be able to survive without oxygen. When we breathe, our lungs take the oxygen we need…