Scientrics

Grenades have played a part in warfare for hundreds of years. They were originally developed around 1000 AD by the Chinese, just on­e application of their r­evolutionary gunpowder technology. Europeans came up with their own versions in the 15th and 16th centuries, with mixed results. The typical design of these early grenades was a hollow metal container filled with gunpowder. Soldiers simply lit a ­wick and tossed the grenade -- as fast as they could. By the 18th century, these weapons had fallen out of favor: They weren't especially useful in the battle style of the time, and the simple design made them extremely dangerous. The weapon saw a resurgence in the 20th century with the development of new modes of combat. In the trench warfare of World War I, soldiers could use grenades to take out machine gunners without ever revealing themselves to the enemy. Thanks to mechanical ignition systems that made the weapons relatively practical and safe, grenades took their plac...

On August 10, 2006, authorities in Great Britain announced that they had arrested several people in connection with a plot to attack airplanes with liquid explosives. The attackers planned to disguise the explosives as ordinary liquids and smuggle them aboard. For this reason, authorities in both the United States and Great Britain warned all passengers that liquids would not be allowed in carry-on luggage until the crisis passed. The ban on liquids included hair spray, shampoo and beverages -- items people travel with all the time. AP Photo/Kevin Wolf A trash container overflows with water bottles and other liquid items near the security checkpoint at Dulles Airport on August 10, 2006, in Chantilly, Va. So what exactly are liquid explosives, and what do they do? Most explosives work in basically the same way. They burn or decompose very quickly, producing lots of heat and gas, which rapidly expands and can tear things apart. Usually, an explosive material requires some kind...

Mayan mathematical system-1-20 Mayan Numbers and Math Along with their advances to the calendar -- like the Tzolk'in, the Haab, and the Long Count -- the Mayans also created their own math system. They used a series of dots and bars to signify numbers. One dot equaled one unit while one bar equaled five units. A shell symbol signified zero. In a system similar to the one we use now, the Mayans used place values to designate large numbers. However, the similarities end there. Mayan math - 27Mayan math - 29 Their place values are vertical, where ours are horizontal. For instance, we write the number 27 horizontally -- the number 2, then the number 7 to the right of it. The Mayans, however, would write 27 vertical­ly -- their symbol for 7 (a line with 2 dots over it) would be on the bottom, and the symbol for 20 (a dot on the line above) would be directly over it. The same applies for other numbers, like 29.

The Long Count Calendar Topical Press Agency/ Getty Images A Mayan calendar column was found in Quirigua, Yucatan peninsula, Mexico, on August 13, 1929. Unfortunately, the Long Count calendar isn't as simple as combining two calendars together to get new dates. It'­s a little more complicated and abstract. In order to understand the Long Count, you first need to become familiar with a few terms: One day - kin 20 days - uinal 360 days - tun 7,200 days - katun 144,000 days - baktun The span of the Long Count calendar is called the Great Cycle , and lasts approximately 5,125.36 years [source: Jenkins ]. To find the Lon­g Count date that corresponds with any Gregorian date, you'll need to count the days from the beginning of the last Great Cycle. But determining when the last cycle began and matching that up to a Gregorian date is quite a feat. English anthropologist Sir Eric Thompson set out to determine the date, and he looked to the Spani...

The Haab Calendar and the Calendar Round mayan calendar in stoneThe Haab calendar is very similar to the Gregorian calendar that we use today. It's based on the cycle of the sun, and was used for agricultural, economic and accounting activities. Much like the Tzolk'in calendar, it's also comprised of uinals, and each day has its own hieroglyph and number. However, instead of using 13 uinals for 260 days, the Haab calendar has 18 uinals, giving it 360 days. Astronomers noticed that 360 days wasn't enough time for the sun to make it through a full solar cycle. They argued that the calendar should follow the cycle as closely as it could in order to be as accurate as possible. However, Mayan mathematicians didn't see it that way. They wanted to keep things simple, in increments of 20, just like their math system. The astronomers and mathematicians finally agreed on the 18 uinals, with five "nameless days" called the wayeb [source: The Maya Calendar]. The wa...

The Tzolk'in Calendar The Tzolk'in calendar was the first one used by the Mayans . Most calendars used throughout Mesoamerica consisted of 260 days. The Tzolk'in, or Sacred Round, calendar followed suit. One theory for its length is that 260 days is the length of pregnancy , and the calendar was based on that [source: Maya Mystery School ]. Another states that it was the length of time to cultivate corn. It's more likely that it was based on numbers. Numbers had great significance in the Mayan culture. For example, the number 20 signifies the number of digits a person has -- 10 fingers and 10 toes. The number 13 refers to the major joints in the human body where it's believed disease and illness enter and attack -- one neck, two shoulders, two elbows, two wrists, two hips, two knees and two ankles [source: Garcia ]. The number 13 also represented the levels of heaven where sacred lords ruled the Earth [source: Tzolk'in Calendar ]. It's these numbe...

A traditional Mayan calendar Most people around the globe look at some form of a calendar every single day. ­Business executives check to see when their meetings are scheduled. The busy mom confirms soccer practices and piano lessons. College students ensure that their papers are turned in on time and they have plenty of time to study for their history exams. For the people of ancient Maya, calendars were just as important to daily life as they are to people today. In this article, we'll look at how the Mayan calendar came to be and the meaning behind each type of calendar the Mayans created. First, let's get a little background on the Mayans. The Mayans originated in a region called Mesoamerica , or Middle America. This region lies in between Mexico and South America and was home to many other cultures, including the Aztec , Olmec, Teotihuacan and Toltec. The Mayans lived in what are today's Guatemala , Belize , Honduras , El Salvador and Southern Me...

© iStockPhoto /dlstudio The end of the world may resemble another ice age. The Long Count to the End The May­ans have a complex system of calendars, and each calendar has a differen­t purpose. There are thought to be 20 calendars in use, though only 15 have been revealed to the public. The Mayans keep the other five a secret within t­heir culture. Some of the more commonly known Mayan calendars are: The Tzolk'in Calendar - Used primarily in crop rotation, this calendar allows one 260-day period to ready the land and one 260-day period to grow and harvest the corn. The Haab Calendar - This calendar lasts 360 days, with a 5-day period called the wayeb. Close to the Gregorian calendar we use today, this calendar follows the cycle of the sun . The Calendar Round - The Calendar Round gave the Mayans a way to record history in longer increments. It's a combination of the Tzolk'in and Haab calendars and goes through about 52 years. Fifty-two years was longer than the Mayans...

There have been countless theories throughout time about how the world will end and how -- ­or if -- life will cease to exist. At the turn of the 21st century, conspiracy theorists claimed that the Y2K bug was only a small part of the impending devastation: The new century would bring about total destruction, and no one would survive. Others believe that Earth is slated for another ice age, which will kill off all living things. And according to astronomers, billions of years from now, the s­un will become a red giant, expanding to a size larger than the Earth's orbit and consuming the Earth in the process. Even if the planet somehow survives, the sun will eventually shrink, becoming a white dwarf and gradually cooling off until it can no longer warm anything in the solar system.In 2006, Mel Gibson released a movie about the Mayan civilization. "Apocalypto" follows one man's journey from slavery back to his family. During the course of the movie, a young woman prophes...

A Sense of Scale At roughly minus 460 F, absolute zero is abysmally cold, yet at least we can imagine it. Being only a few hundred degrees below zero, it's in the realm of something we can put our minds around. This is not true of the opposite of absolute zero, the theoretical highest possible temperature. In conventional physics, this is approximately 100,000,000,000,000,000,000,000,000,000,000 degrees. In this interactive, get a taste of temperatures from absolute zero to absolute hot , and see why, for instance, even the core of the sun is relatively "chilly" compared to what many physicists believe the temperature of the universe was an instant after the Big Bang.— Glenn Elert Launch interactive This feature requires Flash, a free software plug-in, and JavaScript. Install Flash . Glenn Elert is Research Coordinator and Webmaster for the Physical Science Department of Midwood High School at Brooklyn College....

Is there an opposite to absolute zero? Seems like an innocent enough question, right? Absolute zero is 0 on the Kelvin scale, or about minus 460 F. You can't get colder than that; it would be like trying to go south from the South Pole. Is there a corresponding maximum possible temperature? Well, the answer, depending on which theoretical physicist you ask, is yes, no, or maybe. Huh? you ask. Yeah, that's how I felt. And the question doesn't just mess with the minds of physics dummies like me. Several physicists begged off of trying to answer it, referring me to colleagues. Even ones who did talk about it said things like "It's a little bit out of my comfort zone" and "I think I'd like to ruminate over it." After I posed it to one cosmologist, there was dead silence on the other end of the line for long enough that I wondered if we had a dropped call. I had touched a nerve, because, unbeknownst to me, the highest-...