Greatest mysteries of the world

Greatest mysteries of the world

Bigfoot

Bigfoot, also known as “Sasquatch,” is an ape-like creature reputed to inhabit remote forests, particularly in the US and Canada. It is described as being twelve feet tall, walking upright, and covered in dark brown or dark reddish hair. It's known as “Yeti” in Tibet and Nepal, “Yeren” in mainland China, and the “Yowie” in Australia. Whether Bigfoot is an alien creature from another galaxy or an elaborate hoax - or indeed real, the mystery has remained unsolved since centuries.

Bermuda Triangle

An unknown number of ships and aircraft have vanished without a trace here. Situated in the northwestern Atlantic Ocean between the coast of Florida and the islands of Puerto Rico and Bermuda, Bermuda Triangle has claimed everything from charter boats to large surface vessels, from small pvt airplanes to large commercial airliners, with passengers and crew never heard from again. Many believe that an extraterrestrial influence gives this portion of the ocean menacing power.

Egyptian Sphinx

Depicting a reclining half-human, half-lion mythological figure, the Egyptian Sphinx is the earliest known monumental sculpture. It's believed that it was built by the ancient Egyptians as the great protector. A treasure of untold value or even from an extraterrestrial culture is believed to be buried beneath this famous statue. Mystery has surrounded the Great Sphinx for nearly five thousand years, yet the Egyptian govt has been reluctant to let anyone solve the riddle. 

Machu Picchu

Machu Picchu - a Pre-Columbian city in Peru was constructed around 1450, at the height of the Inca Empire, and was abandoned less than 100 years later, as the empire collapsed. Few knew of its existence until 1911, when it was brought to the world’s attention. It is said that the silhouette of the mountain range behind Machu Picchu represents the face of the Inca looking upwards, while the largest peak, Huayna Picchu , represents his pierced nose. It is often referred to as "The Lost City of the Incas".

King Tut’s tomb

In 1922, the richest tomb in archeological history was opened in the Egyptian Valley of the Kings. The tomb of King Tutankhamen - an Egyptian pharaoh of the 18th dynasty - had been untouched for 3,300 years before it was opened. Mystery surrounds the cause of the famous king's death and the unexplained deaths of the many of the researchers who opened the tomb. Many believe it to be the 'Curse of King Tut' which unleashed punishment and death on those who opened the tomb. 

How the Physics of Football Works

How the Physics of Football Works

When you throw a football across the yard to your friend, you are using physics. You make adjustments for all the factors, such as distance, wind and the weight of the ball. The farther away your friend is, the harder you have to throw the ball, or the steeper the angle of your throw. This adjustment is done in your head, and it's physics -- you just don't call it that because it comes so naturally

Fred Beasley of the 49ers running the ball.

Physics is the branch of science that deals with the physical world. The branch of physics that is most relevant to football is mechanics, the study of motion and its causes. We will look at three broad categories of motion as they apply to the game:

• Delivery of a football through the air
• Runners on the field
• Stopping runners on the field
  

Watching a weekend football game could be teaching you something other than who threw the most passes or gained the most yards. Football provides some great examples of the basic concepts of physics -- it's present in the flight of the ball, the motion of the players and the force of the tackles. In this article, we'll look at how physics applies to the game of football.

Throwing the Football

Talking Physics Acceleration - Rate of change of velocity with respect to time (calculated by subtracting the starting velocity from the final velocity and dividing the difference by the time required to reach that final velocity) Force - influence on a body that causes it to change speed or direction Velocity - Speed and direction that an object travels (distance traveled divided by the elapsed amount of time) Speed - How quickly an object moves (distance traveled divided by the elapsed amount of time)

When the football travels through the air, it always follows a curved, or parabolic, path because the movement of the ball in the vertical direction is influenced by the force of gravity. As the ball travels up, gravity slows it down until it stops briefly at its peak height; the ball then comes down, and gravity accelerates it until it hits the ground. This is the path of any object that is launched or thrown (football, arrow, ballistic missile) and is called projectile motion. To learn about projectile motion as it applies to football, let's examine a punt (Figure 1). When a punter kicks a football, he can control three factors:

• The velocity or speed at which the ball leaves his foot
• The angle of the kick
• The rotation of the football

The rotation of the ball -- spiral or end-over-end -- will influence how the ball slows down in flight, because the ball is affected by air drag. A spiraling kick will have less air drag, will not slow down as much and will be able to stay in the air longer and go farther than an end-over-end kick. The velocity of the ball and the angle of the kick are the major factors that determine:

• How long the ball will remain in the air (hang-time)
• How high the ball will go
• How far the ball will go

The angle of a kick helps determine how far it will travel.

When the ball leaves the punter's foot, it is moving with a given velocity (speed plus angle of direction) depending upon the force with which he kicks the ball. The ball moves in two directions, horizontally and vertically. Because the ball was launched at an angle, the velocity is divided into two pieces: a horizontal component and a vertical component. How fast the ball goes in the horizontal direction and how fast the ball goes in the vertical direction depend upon the angle of the kick. If the ball is kicked at a steep angle, then it will have more velocity in the vertical direction than in the horizontal direction -- the ball will go high, have a long hang-time, but travel a short distance. But if the ball is kicked at a shallow angle, it will have more velocity in the horizontal direction than in the vertical direction -- the ball will not go very high, will have a short hang-time, but will travel a far distance. The punter must decide on the best angle in view of his field position. These same factors influence a pass or field goal. However, a field goal kicker has a more difficult job because the ball often reaches its peak height before it reaches the uprights.

Football by the Numbers

Since physics is a quantitative science, developing some units and measures is a good way to begin to understand the effects of physics on football. Consider these useful numbers and units 

• Player at full speed - ~22 miles per hour (9.8 m/s)
• Linebacker - ~220 pounds (98 kg)
• Offensive lineman - ~300 pounds (133 kg)

Punting: Hang-Time, Peak Height and Range

The parabolic path of a football can be described by these two equations:

• y = V_yt - 0.5gt²
• x =V_xt
  • y is the height at any time (t)
  • V_y is the vertical component of the football's initial velocity
  • g is acceleration due to Earth's gravity, 9.8 m/s²
  • x is the horizontal distance of the ball at any time (t)
  • V_x is the horizontal component of the football's initial velocity

To calculate the hang-time (t_total), peak height (y_max), and maximum range (x_max) of a punt, you must know the initial velocity (V) of the ball off the kicker's foot, and the angle (theta) of the kick.

1. The velocity must be broken into horizontal (V_x) and vertical (V_y) components according to the following formulas:
   • V_x = V cos(theta)
   • V_y = V sin(theta)
2. The hang-time (t_total) must be determined by one of these two formulas:
   • t_total = (2V_y/g)
   • t_total = (0.204V_y)
3. Once you know the hang-time, you can calculate maximum range (x_max):
   • x_max = V_x t_total
4. You can calculate the time (t_1/2) at which the ball is at its peak height:
   • t_1/2 = 0.5 t_total
5. And you can calculate the peak height (y_max), using one of these two formulas:
   • y_max = v_y(t_1/2) - 1/2g(t_1/2)²
   • y_max = v_y(t_1/2) - 0.49(t_1/2)²

For example, a kick with a velocity of 90 ft/s (27.4 m/s) at an angle of 30 degrees will have the following values:

1. Vertical and horizontal components of velocity:
   • V_x = V cos(theta) = (27.4 m/s) cos (30 degrees) = (27.4 m/s) (0.0.87) = 23.7 m/s
   • V_y = V sin(theta) = (27.4 m/s) sin (30 degrees) = (27.4 m/s) (0.5) = 13.7 m/s
2. Hang-time:
   • t_total = (0.204V_y) = {0.204 (13.7m/s)} = 2.80 s.
3. Maximum range:
   • x_max = V_x t_total = (23.7 m/s)(2.80 s) = 66.4 m
   • 1 m = 1.09 yd
   • x_max = 72 yd
4. Time at peak height:
   • t_1/2 = 0.5 t_total = (0.5)(2.80 s) = 1.40 s
5. Peak height:
   • y_max = V_y(t_1/2) - 0.49(t_1/2)² = [{(13.7 m/s)(1.40 s)} - {0.49(1.40 s)²}] = 18.2 m
   • 1 m = 3.28 ft
   • y_max = 59.7 ft

If we do the calculations for a punt with the same velocity, but an angle of 45 degrees, then we get a hang-time of 3.96 s, a maximum range of 76.8 m (84 yd), and a peak height of 36.5 m (120 ft). If we change the angle of the kick to 60 degrees, we get a hang-time of 4.84 s, a maximum range of 66.3 m (72 yd), and a peak height of 54.5 m (179 ft). Notice that as the angle of the kick gets steeper, the ball hangs longer in the air and goes higher. Also, as the angle of the kick is increased, the distance traveled by the ball increases to a maximum (achieved at 45 degrees) and then decreases.

Runners on the Field

When we look at runners on the field, several aspects can be considered:

• Where they line up for a play
• Changing directions
• Running in an open field

Line-Up Positions 

When we look at the positions of the backs, both offensive and defensive, we see that they typically line up away from the line of scrimmage on either side of the offensive and defensive linemen. Their positioning allows them room, or time, to accelerate from a state of rest and reach a high speed, to either run with the ball or pursue the ball carrier. Notice that the linebackers have far more room to accelerate than the linemen, and the wide receivers have far more room than the linebackers. So linebackers can reach higher speeds than linemen, and wide receivers can reach the highest speeds of all.

Changing Directions on the Field 

Let's look at an example of a running play in which the quarterback hands the ball off to a running back. First, the running back starts from the set position, at rest, and accelerates to full speed (22 mi/h or 9.8 m/s) in 2 s after receiving the ball. His acceleration (a) is:

• a = (v_f - v_o)/(t_f - t_o)
  • v_f is final velocity
  • v_o is initial velocity
  • t_f is final time
  • t_o is initial time
• a=(9.8 m/s - 0 m/s)/(2 s - 0 s)
• a= 4.9 m/s²

As he runs with the flow of the play (e.g. to the right), he maintains constant speed (a = 0). When he sees an opening in the line, he plants his foot to stop his motion to the right, changes direction and accelerates upfield into the open. By planting his foot, he applies force to the turf. The force he applies to the turf helps to accomplish two things:

• Stop his motion to the right
• Accelerate him upfield

To stop his motion to the right, two forces work together. First, there is the force that he himself applies to the turf when he plants his foot. The second force is there between his foot and the turf. Friction is an extremely important factor in runners changing direction. If you have ever seen a football game played in the rain, you have seen what happens to runners when there is little friction to utilize. The following is what happens when a runner tries to change his direction of motion on a wet surface:

1. As he plants his foot to slow his motion, the coefficient of friction between the turf and him is reduced by the water on the surface.
2. The reduced coefficient of friction decreases the frictional force.
3. The decreased frictional force makes it harder for him to stop motion his to the right.
4. The runner loses his footing and falls.

The applied force and the frictional force together must stop the motion to the right. Let's assume that he stops in 0.5 s. His acceleration must be:

• a = (0 m/s - 9.8 m/s)/(0.5 s - 0 s)
• a = -19.6 m/s²
  *The negative sign indicates that the runner is accelerating is in the opposite direction, to the left.

Talking Physics Mass - The amount of substance that an object contains Momentum - The mathematical product of the mass of a moving object and its velocity Impulse - The mathematical product of force and the time over which that force is applied to an object

The force (F) required to stop him is the product of his mass (m), estimated at 98 kg (220 lbs), and his acceleration:

• F = ma = (98 kg)(-19.6 m/s²) = 1921 Newtons (N)
• 4.4 N = 1 lb
• F = ~500 lbs!

To accelerate upfield, he pushes against the turf and the turf applies an equal and opposite force on him, thereby propelling him upfield. This is an example of Isaac Newton's third law of motion, which states that "for every action there is an equal, but opposite reaction." Again, if he accelerates to full speed in 0.5 s, then the turf applies 1921 N, or about 500 lbs, of force. If no one opposes his motion upfield, he will reach and maintain maximum speed until he either scores or is tackled.

Running in an Open Field 

When running in an open field, the player can reach his maximum momentum. Because momentum is the product of mass and velocity, it is possible for players of different masses to have the same momentum. For example, our running back would have the following momentum (p):

• p = mv = (98 kg)(9.8 m/s) = 960 kg-m/s

For a 125 kg (275 lb) lineman to have the same momentum, he would have to move with a speed of 7.7 m/s. Momentum is important for stopping (tackling, blocking) runners on the field.

Blocking and Tackling

Tackling and blocking runners relies on three important principles of physics:

• Impulse
• Conservation of momentum
• Rotational motion

Photo courtesy North Carolina State University

Players use physics to stop each other on the football field.

When Runner and Tackler Meet

When our running back is moving in the open field, he has a momentum of 960 kg-m/s. To stop him -- change his momentum -- a tackler must apply an impulse in the opposite direction. Impulse is the product of the applied force and the time over which that force is applied. Because impulse is a product like momentum, the same impulse can be applied if one varies either the force of impact or the time of contact. If a defensive back wanted to tackle our running back, he would have to apply an impulse of 960 kg-m/s. If the tackle occurred in 0.5 s, the force applied would be:

• F = impulse/t = (960 kg-m/s)/(0.5 s) = 1921 N = 423 lb

Alternatively, if the defensive back increased the time in contact with the running back, he could use less force to stop him.

In any collision or tackle in which there is no force other than that created by the collision itself, the total momentum of those involved must be the same before and after the collision -- this is the conservation of momentum. Let's look at three cases:

1. The ball carrier has the same momentum as the tackler.
2. The ball carrier has more momentum than the tackler.
3. The ball carrier has less momentum than the tackler.

For the discussion, we will consider an elastic collision, in which the players do not remain in contact after they collide.

1. If the ball carrier and tackler have equal momentum, the forward momentum of the ball carrier is exactly matched by the backward momentum of the tackler. The motion of the two will stop at the point of contact.
2. If the ball carrier has more momentum than the tackler, he will knock the tackler back with a momentum that is equal to the difference between the two players, and will likely break the tackle. After breaking the tackle, the ball carrier will accelerate.
3. If the ball carrier has less momentum than the tackler, he will be knocked backwards with a momentum equal to the difference between the two players.

In many instances, tacklers try to hold on to the ball carrier, and the two may travel together. In these inelastic collisions, the general reactions would be the same as those above; however, in cases 2 and 3, the speeds at which the combined players would move forward or backward would be reduced. This reduction in speed is due to the fact that the difference in momentum is now distributed over the combined mass of the two players, instead of the mass of the one player with the lesser momentum.

The Tackling Process

Coaches often tell their players to tackle a runner low. In this way, the runner's feet will be rotated in the air in the direction of the tackle. Let's look at this closely:

Tackling a runner low requires less force because the tackler is farther away from the runner's center of mass.

Talking Physics Center of mass - The point in a body's distribution of mass at which all of the mass can be considered to be concentrated. Torque - A force that tends to produce rotation or twisting

Imagine that the runner's mass is concentrated in a point called thecenter of mass. In men, the center of mass is located at or slightly above the navel; women tend to have their center of mass below their navels, closer to their hips. All bodies will rotate easiest about their center of mass. So, if a force is applied on either side of the center of mass, the object will rotate. This rotational force is called torque, and is the product of the amount of force applied and the distance from the center of mass at which the force applied. Because torque is a product, the same torque can be applied to an object at different distances from the center of mass by changing the amount of force applied: Less force is required farther out from the center of mass than closer in. So, by tackling a runner low -- far from the center of mass -- it takes less force to tackle him than if he were tackled high. Furthermore, if a runner is hit exactly at his center of mass, he will not rotate, but instead will be driven in the direction of the tackle.

A lineman crouches low so that his center of mass is closer to the ground. This makes it hard for an opposing player to move him.

Similarly, coaches often advise linemen to stay low. This brings their center of mass closer to the ground, so an opposing player, no matter how low he goes, can only contact them near their center of mass. This makes it difficult for an opposing player to move them, as they will not rotate upon contact. This technique is critical for a defensive lineman in defending his own goal in the "red" zone, the last 10 yards before the goal line.

Thanks!Special thanks to Dr. David Haase, professor of physics and director of The Science House at North Carolina State University in Raleigh, NC.

We have only touched on some of the applications of physics as they relate to football. Remember, this knowledge appears to be instinctive; Most often, players and coaches don't consciously translate the mechanics of physics into their playing of the sport. But by making that translation, we can understand and appreciate even more just how amazing some of the physical feats on the football field really are. Also, applying physics to football leads to better and safer equipment, affects the rules of the sport, improves athletic performance, and enhances our connection to the game.

What if everybody in the United States flushed the toilet at the same time?

What if everybody in the United States flushed the toilet at the same time?

Nov. 19 is World Toilet Day, a time to reflect upon how far modern sanitation has come. In the United States in 2005, less than half of one percent of the country's more than 124 million households didn't have a flushing toilet [source: U.S. Census Bureau]. In comparison, 71 percent of India's total population of more than one billion people had no access to a toilet that same year. There were an estimated 350 million public and private toilets in the United States by the mid-1990s [source: Flushmate] -- a lot of toilets by anyone's measure. So what would happen if everyone in the United States decided to flush their toilets at the same time in celebration of World Toilet Day?

Since as far as we could find out -- no one's ever tried it before -- we can't say for certain exactly what would happen. But we can take a pretty good guess: "It would be ugly," says Steve Cox, one wastewater treatment facility operator we interviewed.

If everyone in the United States flushed the toilet at the same time, sewer systems across the country would be overwhelmed with wastewater.

The average home in America is outfitted with sewer pipes around four inches in diameter. The pipes from your home are connected to subdivision systems, which connect together at street systems. Street systems tie into road systems, which go to main road systems, and, ultimately, waste treatment plants. Underneath your town is a wastewater system as complex as a spider's web.

The closer you get to the treatment plant, the larger the inside diameter of the pipes becomes. So a four-inch pipe from your house connects to a 12-inch pipe and so on, until -- in larger cities -- pipes may be almost 10 feet in diameter. A pipe this size can hold a lot of water, but can it hold enough for everyone to flush at once?

If everyone in each of Milwaukee, Wisconsin's 330,584 households all flushed just one toilet at the same time, and each of those toilets expelled 3.5 gallons per flush, then Milwaukee's sewer system would suddenly be inundated with 1,157,044 gallons of wastewater [source]. Even with the city's new 108-inch pipes, this could be a problem, and we're not even counting all of the public toilets in the city.

Of course, the earth isn't level underneath many cities, and to overcome changes in elevation, sewer systems use lift stations, wastewater plants that push sewage uphill toward its final treatment destination. These stations would be the first overwhelmed by unanimous flushing. There would simply be too much wastewater trying to pass through the pipes at the same time -- kind of like trying to force an orange through a drinking straw -- and the flow of sewage would stop. Sewage already past the lift stations would return downhill, and as the lift stations flooded, the lines leading to them would back up.

Eventu ally this sewage would find its way to the place where this whole debacle originated -- your home. Backflow valves probably wouldn't help. Not only would your toilet overflow, but so, too, would every wastewater line in your home, including your shower, kitchen and bathroom sinks, and even your dishwasher and washing machine.

Outside, the manhole covers dotting the street would also flood and overflow, leaving people in sewage possibly more than ankle deep. Depending on how many people live in your city and how large the sewer pipes are, it could be even worse.

-flow Toilets: A Lot Less Mess

If everyone in Milwaukee conducted the same experiment from the first page using only low-flowtoilets, only 528,934 gallons of wastewater would suddenly deluge the city's sewer system. This would still cause quite a mess, but it would correct itself much faster, and the water pressure would equalize more quickly, too.

But low-flow toilets weren't designed to save Milwaukee from a public health hazard and an environmental catastrophe. They were designed to conserve water. And they have become so valuable at serving this purpose that they have replaced traditional toilets in stores. In fact, it is federal law that no toilet may be produced in the United States that uses more than 1.6 gallons per flush.

China Photos/Getty Images In Beijing, China, a very low-flow toilet is demonstrated using only a half-gallon of water.

When they were first introduced in the early 1990s, low-flow (or low-flush) toilets were accepted warily by consumers in the United States. They clogged easily, and even when the toilets didn't clog, they often failed to do their job on the first try. Some consumers griped that they had to flush the toilet more than once. If a homeowner had to flush a low-flow toilet three times, then he or she used 4.8 gallons, more than a gallon more than with a traditional toilet. Some Americans became so fed up with low-flow toilets that they crossed the northern border into Canada to purchase 3.5-gallon toilets, since none were available for sale back in the States. But low-flow technology has improved since the '90s, and the next generation of low-flow toilets appears to combine improved function with water conservation.

The United States Environmental Protection Agency (EPA) suggests that consumers in the market for a toilet should look for the WaterSense label. This certification is given to toilets that use no more than 1.28 gallons per flush, verified by testing at independent laboratories.

The EPA estimates that the average American will flush the toilet around 140,000 times in his or her lifetime. Since the amount of available water has become a real issue in the United States in the past few years, low-flow toilets are helping to allay a growing problem. The EPA is not the only governmental agency encouraging Americans to replace their toilets with low-flow toilets: Some American municipalities are offering $50 and $100 rebates as incentives for homeowners to make the switch. If everyone in the United States used only WaterSense toilets, the country would save an estimated 900 million gallons of water per day, equal to roughly twenty minutes of flow over Niagara Falls [source].

Just the savings alone (around $90 per year on your water bill) is reason enough for many people. But don't forget to take into account that if everyone switched to WaterSense toilets, it would cut the amount of mess caused by everyone flushing their toilets at the same time by more than half. And avoiding ankle-deep sewage is good for everyone.

How Light Propulsion Will Work

How Light Propulsion Will Work

More than 20 years ago, the United States began to develop a missile defense system that was given the nickname "Star Wars." This system was designed to track and use lasers to shoot down missiles launched by foreign countries. While this system was designed for war, researchers have found many other uses for these high-powered lasers. In fact, lasers could one day be used to propel spacecraft into orbit and to other planets.

An early model of a laser-propelled lightcraft

To reach space, we currently use the space shuttle, which has to carry tons of fuel and have two massive rocket boosters strapped to it to lift off the ground. Lasers would allow engineers to develop lighter spacecraft that wouldn't need an onboard energy source. The lightcraft vehicle itself would act as the engine, and light -- one of the universe's most abundant power sources -- would be the fuel.

A lightcraft in action. The bright light you see is the air combusting under the rim of the craft.

The basic idea behind light propulsion is the use of ground-based lasers to heat air to the point that it explodes, propelling the spacecraft forward. If it works, light propulsion will be thousands of times lighter and more efficient than chemical rocket engines, and will produce zero pollution. In this edition of How Stuff WILL Work, we'll take a look at two versions of this advanced propulsion system -- one may take us from the Earth to the moon in just five and a half hours, and the other could take us on a tour of the solar system on "highways of light."

Laser-propelled Lightcraft

Light-propelled rockets sound like something out of science fiction -- spacecraft that ride on a laser beam into space, require little or no onboard propellant and create no pollution. Sounds pretty far-fetched, considering we haven't been able to develop anything close to that for conventional ground- or air-travel on Earth. But while it may still be 15 to 30 years away, the principles behind the lightcraft have already been successfully tested several times. A company called Lightcraft Technologies continues to refine the research that began at Rensselaer Polytechnic Institute in Troy, N.Y.

Photo courtesy Rensselaer As the laser pulses, it superheats the air until it combusts. Each time the air combusts, it creates a flash of light, as seen in this photo of a test flight.

The basic idea for the lightcraft is simple -- the acorn-shaped craft uses mirrors to receive and focus the incoming laser beam to heat air, which explodes to propel the craft. Here's a look at the basic components of this revolutionary propulsion system:

• Carbon-dioxide laser - Lightcraft Technologies uses a Pulsed Laser Vulnerability Test System (PLVTS), an offspring of the Star Wars defense program. The 10 kw pulsed laser being used for the experimental lightcraft is among the most powerful in the world.
• Parabolic mirror - The bottom of the spacecraft is a mirror that the laser beam into the engine air or onboard propellant. A secondary, ground-based transmitter, telescope-like mirror is used to direct the laser beam onto the lightcraft.
• Absorption chamber - The inlet air is directed into this chamber where it is heated by the beam, expands and propels the lightcraft.
• Onboard hydrogen - A small amount of hydrogen propellant is needed for rocket thrust when the atmosphere is too thin to provide enough air.

Prior to liftoff, a jet of compressed air is used to spin the lightcraft to about 10,000 revolutions per minute (RPMs). The spin is needed to stabilize the craft gyroscopically. Think about football: a quarterback applies spin when passing a football to throw a more accurate pass. When spin is applied to this extremely lightweight craft, it allows the craft to cut through the air with more stability. Once the lightcraft is spinning at an optimal speed, the laser is turned on, blasting the lightcraft into the air. The 10-kilowatt laser pulses at a rate of 25-28 times per second. By pulsing, the laser continues to push the craft upward. The light beam is focused by the parabolic mirror on the bottom of the lightcraft, which heats the air to between 18,000 and 54,000 degrees Fahrenheit (9,982 and 29,982 degrees Celsius) -- that's several times hotter than the surface of the sun. When you heat air to these high temperatures, it is converted to a plasma state -- this plasma then explodes to propel the craft upward.

Lightcraft Technologies, Inc., with FINDS sponsorship -- earlier flights were funded by NASA and the U.S. Air Force -- has tested a small prototype lightcraft several times at the White Sands Missile Range in New Mexico. In October 2000, the miniature lightcraft, which has a diameter of 4.8 inches (12.2 cm) and weighs only 1.76 ounces (50 grams), achieved an altitude of 233 feet (71 meters). Sometime in 2001, Lightcraft Technologies hopes to send the lightcraft prototype up to an altitude of about 500 feet. A 1-megawatt laser will be needed to put a one-kilogram satellite in low earth orbit. Although the model is made of aircraft-grade aluminum, the final, full-size lightcraft will probably be built out of silicon carbide.

This laser lightcraft could also use mirrors, located in the craft, to project some of the beamed energy ahead of the ship. The heat from the laser beam would create an air spike that would divert some of the air past the ship, thus decreasing drag and reducing the amount of heat absorbed by the lightcraft.

Microwave-propelled Lightcraft

Another propulsion system being considered for a different class of lightcraft involves the use of microwaves. Microwave energy is cheaper than laser energy, and easier to scale to higher powers, but it would require a ship that has a larger diameter. Lightcrafts being designed for this propulsion would look more like flying saucers (now we're really heading into the realm of science fiction). This technology will take more years to develop than the laser-propelled lightcraft, but it could take us to the outer planets. Developers also envision thousands of these lightcraft, powered by a fleet of orbiting power stations, that will replace conventional airline travel.

Photo courtesy NASA Microwave-powered lightcraft will rely on orbiting power stations.

A microwave-powered lightcraft will also utilize a power source that is not integrated into the ship. With the laser-powered propulsion system, the power source is ground-based. The microwave propulsion system will flip that around. The microwave-propelled spacecraft will rely on power beamed down from orbiting, solar power stations. Instead of being propelled away from its energy source, the energy source will draw the lightcraft in.

Before this microwave lightcraft can fly, scientists will have to put into orbit a solar power station with a diameter of 1 kilometer (0.62 miles). Leik Myrabo, who leads the lightcraft research, believes that such a power station could generate up to 20 gigawatts of power. Orbiting 310 miles (500 km) above Earth, this power station would beam down microwave energy to a 66-foot (20-meter), disk-shaped lightcraft that would be capable of carrying 12 people. Millions of tiny antennae covering the top of the craft would convert the microwaves into electricity. In just two orbits, the power station would be able to collect 1,800 gigajoules of energy and beam down 4.3 gigawatts of power to the lightcraft for the ride to orbit.

The microwave lightcraft would be equipped with two powerful magnets and three types of propulsion engines. Solar cells, covering the top of the ship, would be used by the lightcraft at launch to produce electricity. The electricity would then ionize the air and propel the craft for picking up passengers. Once it's launched, the microwave lightcraft used its internal reflector to heat the air around it and push through the sound barrier.

Once in a high altitude, it would tilt sideways for hypersonic speeds. Half of the microwave power could then be reflected in front of the ship to heat the air and create an air spike, allowing the ship to cut through the air at up to 25 times the speed of sound and fly into orbit. The craft's top speed peaks at around 50 times the speed of sound. The other half of the microwave power is converted into electricity by the craft's receiving antennae, and used to energize its two electromagnetic engines. These engines then accelerate the slip stream, or the air flowing around the craft. By accelerating the slip stream the craft is able to cancel out any sonic boom, which makes the lightcraft completely silent at supersonic speeds.