Wednesday 24 October 2007

How much water is there on Earth?

There's a whole lot of water on Earth! Something like 326,000,000,000,000,000,000 gallons (326 million trillion gallons) of the stuff (roughly 1,260,000,000,000,000,000,000 liters) can be found on our planet. This water is in a constant cycle -- it evaporates from the ocean, travels through the air, rains down on the land and then flows back to the ocean.

The oceans are huge. About 70 percent of the planet is covered in ocean, and the average depth of the ocean is several thousand feet (about 1,000 meters). Ninety-eight percent of the water on the planet is in the oceans, and therefore is unusable for drinking because of the salt. About 2 percent of the planet's water is fresh, but 1.6 percent of the planet's water is locked up in the polar ice caps and glaciers. Another 0.36 percent is found underground in aquifers and wells. Only about 0.036 percent of the planet's total water supply is found in lakes and rivers. That's still thousands of trillions of gallons, but it's a very small amount compared to all the water available.

The rest of the water on the planet is either floating in the air as clouds and water vapor, or is locked up in plants and animals (your body is 65 percent water, so if you weigh 100 pounds, 65 pounds of you is water!). There's also all the soda pop, milk and orange juice you see at the store and in your refrigerator… There's probably several billion gallons of water sitting on a shelf at any one time!

What is the Year 2038 problem?

The Year 2000 problem is understood by most people these days because of the large amount of media attention it received.

Most programs written in the C programming language are relatively immune to the Y2K problem, but suffer instead from the Year 2038 problem. This problem arises because most C programs use a library of routines called the standard time library . This library establishes a standard 4-byte format for the storage of time values, and also provides a number of functions for converting, displaying and calculating time values.

The standard 4-byte format assumes that the beginning of time is January 1, 1970, at 12:00:00 a.m. This value is 0. Any time/date value is expressed as the number of seconds following that zero value. So the value 919642718 is 919,642,718 seconds past 12:00:00 a.m. on January 1, 1970, which is Sunday, February 21, 1999, at 16:18:38 Pacific time (U.S.). This is a convenient format because if you subtract any two values, what you get is a number of seconds that is the time difference between them. Then you can use other functions in the library to determine how many minutes/hours/days/months/years have passed between the two times.

If you have read How Bits and Bytes Work, you know that a signed 4-byte integer has a maximum value of 2,147,483,647, and this is where the Year 2038 problem comes from. The maximum value of time before it rolls over to a negative (and invalid) value is 2,147,483,647, which translates into January 19, 2038. On this date, any C programs that use the standard time library will start to have problems with date calculations.

This problem is somewhat easier to fix than the Y2K problem on mainframes, fortunately. Well-written programs can simply be recompiled with a new version of the library that uses, for example, 8-byte values for the storage format. This is possible because the library encapsulates the whole time activity with its own time types and functions (unlike most mainframe programs, which did not standardize their date formats or calculations). So the Year 2038 problem should not be nearly as hard to fix as the Y2K problem was.

Sunday 14 October 2007

What is an IP address?

Dear all,

I hope this topic will be more interesting than my previous post. Ofcourse, we are going to discuss on the frequently heard term called "IP". Often, you will check your System IP's everytime by pinging"IPCONFIG" in your command window, it some times mean that you dont have any other work to do. :)

Lets go in to the topic now...

Every machine on the Internet has a unique identifying number, called an IP Address. A typical IP address looks like this:


To make it easier for us humans to remember, IP addresses are normally expressed in decimal format as a "dotted decimal number" like the one above. But computers communicate in binary form. Look at the same IP address in binary:

* 11011000.00011011.00111101.10001001

The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers. Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between 0 and 255. Combine the four octets and you get 232 or a possible 4,294,967,296 unique values!

Out of the almost 4.3 billion possible combinations, certain values are restricted from use as typical IP addresses. For example, the IP address is reserved for the default network and the address is used for broadcasts.

The octets serve a purpose other than simply separating the numbers. They are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need. The octets are split into two sections: Net and Host. The Net section always contains the first octet. It is used to identify the network that a computer belongs to. Host (sometimes referred to as Node) identifies the actual computer on the network. The Host section always contains the last octet. There are five IP classes plus certain special addresses:

* Default Network - The IP address of is used for the default network.

* Class A - This class is for very large networks, such as a major international company might have. IP addresses with a first octet from 1 to 126 are part of this class. The other three octets are used to identify each host. This means that there are 126 Class A networks each with 16,777,214 (224 -2) possible hosts for a total of 2,147,483,648 (231) unique IP addresses. Class A networks account for half of the total available IP addresses. In Class A networks, the high order bit value (the very first binary number) in the first octet is always 0.


Host or Node


* Loopback - The IP address is used as the loopback address. This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing.

* Class B - Class B is used for medium-sized networks. A good example is a large college campus. IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier. The other two octets are used to identify each host. This means that there are 16,384 (214) Class B networks each with 65,534 (216 -2) possible hosts for a total of 1,073,741,824 (230) unique IP addresses. Class B networks make up a quarter of the total available IP addresses. Class B networks have a first bit value of 1 and a second bit value of 0 in the first octet.


Host or Node


* Class C - Class C addresses are commonly used for small to mid-size businesses. IP addresses with a first octet from 192 to 223 are part of this class. Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (221) Class C networks each with 254 (28 -2) possible hosts for a total of 536,870,912 (229) unique IP addresses. Class C networks make up an eighth of the total available IP addresses. Class C networks have a first bit value of 1, second bit value of 1 and a third bit value of 0 in the first octet.


Host or Node


* Class D - Used for multicasts, Class D is slightly different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 0. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class D accounts for 1/16th (268,435,456 or 228) of the available IP addresses.


Host or Node


* Class E - Class E is used for experimental purposes only. Like Class D, it is different from the first three classes. It has a first bit value of 1, second bit value of 1, third bit value of 1 and fourth bit value of 1. The other 28 bits are used to identify the group of computers the multicast message is intended for. Class E accounts for 1/16th (268,435,456 or 228) of the available IP addresses.


Host or Node


* Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address

Hope you would had fun with this one and thereabout will meet you with more special topics.

Monday 8 October 2007

How do they get lead in a wooden pencil?

Hi all,

Take a look at the writing end of a brand-new wooden pencil before sharpening it :);
it appears that the wood casing is one solid piece. This might lead you to believe that pencil-makers bore a hole straight down the middle of the wood and then slide in a rod of lead. Although early pencils were constructed in this manner, it is not how most wooden pencils are mass-produced today.

Before discussing how the lead is put into the wood casing, let's clear up what the actual lead is. Pencil lead is not lead at all; it's a combination of finely ground graphite and clay, mixed with water and pressed together at high temperatures into thin rods. We call it lead is because the Englishmen who first discovered graphite believed they had found lead. According to the Cumberland Pencil Museum, in the mid-16th century, a violent storm knocked over several trees in Borrowdale, England, uncovering a large deposit of a black substance that was first thought to be lead. More than 200 years later, an English scientist discovered that the substance was not actually lead, but a type of carbon instead. The substance was named graphite, after the Greek word meaning "to write," since that's how people used the substance.

Early pencils were crude versions of today's standard model. The first pencil was just a chunk of graphite used by carpenters and artisans to make markings without denting their materials. This evolved into a graphite chunk wrapped in sheepskin, followed by a string-wrapped graphite pencil, the first pencil with a rod-shaped graphite core. To use one of these pencils, the writer would have to unravel the string as the graphite wore down. The next major leap in design was hollowing out a stick of cedar and sticking a piece of graphite down the hole, an idea often credited to the Italians. The English embraced this idea but simplified the manufacturing process considerably. Instead of hollowing out a piece of wood, they simply cut a groove in the wood, inserted a piece of graphite and broke it off level with the top of the groove. They then glued a small slat of wood on top, encasing the graphite.

Today, most wooden pencils are mass produced from large blocks of cedar cut into slats. A machine cuts eight grooves, half as deep as the graphite-clay rod is thick, into the slats, and then places rods in each groove. Once the rods are in place, a second grooved slat is glued on top of the first. When the glue dries, the slats are fed through a cutting machine that cuts the wood into various shapes and divides the slats into eight separate pencils. The seams where the two slats are joined are sanded down and several coats of paint are applied to the pencil, giving it the appearance of a solid structure.

According to Musgrave Pencil Co. Inc, more than 14 billion pencils are produced in the world every year, enough to circle the earth 62 times. This pile of pencils includes a wide variety of styles and widths. If you've ever have taken a fill-in-the-bubble test, you're probably aware that pencils vary in darkness. The number printed on the side of the pencil indicates hardness and darkness of the graphite core: the higher the number, the harder the graphite core. Because a hard core leaves behind less of the graphite-clay mixture on the paper, it will have a fainter mark than a softer core.

Monday 1 October 2007

How many sheets of paper can be produced from a single tree?

Hi all,

In this topic we shall see some how many sheets can be made from a single tree. I guess, its an interesting and useful topic for all.

Let me go to the topic quickly,

It is probably hard to get an exact number, but here is how I would start answer to this question: First, we have to define what a "tree" is. Is it a giant redwood tree or a little weeping willow? Most paper is made from pine trees, so I went out in the woods and looked at some pines. :)

Most are about 1 foot in diameter and 60 feet tall. Ignoring taper, that's about 81,430 cubic inches of wood:

pi * radius2 * length = volume
3.14 * 62 * (60 * 12) = 81,430

I have a 2x4-foot piece of lumber in the backyard. It weighs about 10 pounds and contains 504 cubic inches of wood. That means a pine tree weighs roughly 1,610 pounds (81430/504 * 10).

I know that in manufacturing paper, the wood is turned into pulp. The yield is about 50 percent -- about half of the tree is knots, lignin and other stuff that is no good for paper. So that means a pine tree yields about 805 pounds of paper. I have a ream of paper for a photocopier here and it weighs about 5 pounds and contains 500 sheets (you often see paper described as "20-pound stock" or "24-pound stock" -- that is the weight of 500 sheets of 17" x 22" paper). So, using these measurements, a tree would produce (805/5 * 500) 80,500 sheets of paper.

These are all fairly rough estimations.

How much does planet Earth weigh?

Hi all,

Lets now concentrate on a science topic,How much does planet Earth weigh?

It would be more proper to ask, "What is the mass of planet Earth?"1 The quick answer to that is: approximately 6,000,000,000,000,000,000,000,000 (6E+24) kilograms.

The interesting sub-question is, "How did anyone figure that out?" It's not like the planet steps onto the scale each morning before it takes a shower. The measurement of the planet's weight is derived from the gravitational attraction that the Earth has for objects near it.

It turns out that any two masses have a gravitational attraction for one another. If you put two bowling balls near each other, they will attract one another gravitationally. The attraction is extremely slight, but if your instruments are sensitive enough you can measure the gravitational attraction that two bowling balls have on one another. From that measurement, you could determine the mass of the two objects. The same is true for two golf balls, but the attraction is even slighter because the amount of gravitational force depends on mass of the objects.

Newton showed that, for spherical objects, you can make the simplifying assumption that all of the object's mass is concentrated at the center of the sphere. The following equation expresses the gravitational attraction that two spherical objects have on one another:
F = G * M1 * M2 / R2

* R is the distance separating the two objects.
* G is a constant that is 6.67259x10-11m3/s2 kg.
* M1 and M2 are the two masses that are attracting each other.
* F is the force of attraction between them.

Assume that Earth is one of the masses (M1) and a 1-kg sphere is the other (M2). The force between them is 9.8 kg*m/s2 -- we can calculate this force by dropping the 1-kg sphere and measuring the acceleration that the Earth's gravitational field applies to it (9.8 m/s2).

The radius of the Earth is 6,400,000 meters (6,999,125 yards). If you plug all of these values in and solve for M1, you find that the mass of the Earth is 6,000,000,000,000,000,000,000,000 kilograms (6E+24 kilograms / 1.3E+25 pounds).

It is "more proper" to ask about mass rather than weight because weight is a force that requires a gravitational field to determine. You can take a bowling ball and weigh it on the Earth and on the moon. The weight on the moon will be one-sixth that on the Earth, but the amount of mass is the same in both places. To weigh the Earth, we would need to know in which object's gravitational field we want to calculate the weight. The mass of the Earth, on the other hand, is a constant.