In some ways, Roman numbering worked like the modern Arabic numeral system where, starting from the left, there are thousands, hundreds, tens and individual units. However, Roman numerals are quite different. One thousand is written as M, five hundred as D, one hundred as C, fifty as L, ten as X and five as V.
Picture credit: google
The decimal system describes a numbering system for calculation based on multiples of ten. Multiplying or dividing a number by ten is very easy because only the decimal point needs to be moved. In the decimal system, each number has a value ten times that of the next number to the right. For instance, 5,283 means five thousands, two hundreds, eight tens and three ones. The decimal point simply separates the main number from numbers less than one. The number ten has always been important in mathematics — you can easily count it on your fingers.
Picture credit: google
The metric system is a group of various units of measurement. Its name comes originally from the metre. It is a decimal system, which means that each unit is ten times bigger, or smaller, than the next unit. Previously, measurements were difficult to calculate; in measurements of length, for example, there were 12 inches in one foot and three feet in one yard, while weight was calculated using ounces and pounds (16 ounces in one pound).
The metric system was devised in the 1790s in France, and is now used in most countries in the world for all scientific and technical measurements.
Picture credit: google
Numbers are used to describe the amount of things. We can express numbers in words, by hand gestures or in writing, using symbols or numerals. When we talk about a number we use words (‘five’) rather than the numeral (5), but when we write we use both words and numerals.
Numbers can describe how many objects there are or their position among lots of objects, such as 1st or 5th for example. Other types of numbers describe how many units of something there are, for example how many kilograms (weight) or metres (length).Numbers are just a convenient way to describe ideas.
Picture credit: google
Calendars have been used for thousands of years. The early ones were usually based on the phases of the Moon and the movement of the Sun. We still depend largely on the natural movements of the Earth, Moon and Sun to divide up time. The calendar we use today is based on the Julian calendar, which, was introduced by the Romans in 46 BC. It had 365 days, and the Romans had not yet discovered the need for leap years. By 1582 the Julian calendar was ten days out, and Pope Gregory decreed that ten days would have to go missing from that year. This caused rioting because people felt that ten days of their lives had been stolen.
Picture credit: google
In 1884 an international conference decided that the 0 degree line of longitude, or meridian, would run through the Royal Observatory in Greenwich, England. As you move to the east from the Greenwich Meridian, the time is one hour ahead of Greenwich Mean Time for each degree you move. If you move to the west, time is one hour behind for each degree. Midday is the point where the Sun is highest in the sky, whichever time zone you are in.
The amount of daylight varies with the seasons, so daylight - saving time or summer time, was introduced to make maximum use of daylight hours. In the northern hemisphere, clocks are reset one hour ahead in spring and one hour back in autumn. (In the southern hemisphere the seasons are reversed.
Picture credit: google
After the invention of sundials, other means of telling the time indoors were developed, such as hourglasses and burning candles. The invention of clocks, however, allowed far more accurate timekeeping. Early clocks were powered by a weight hanging from a fine chain (a pendulum), but later on springs were used to store energy. Most mechanical clocks and watches now contain a balance wheel that spins backwards and forwards, allowing an escapement wheel to move a very small amount each time it spins. This wheel is driven by the energy stored in the clock spring.
Many watches and clocks are now powered by an electronic timer with no moving parts. It contains a tiny integrated circuit and a vibrating quartz crystal, which measures time with great accuracy.
Picture credit: google
The Earth spins on its own axis once every 24 hours, or day. The Earth orbits the Sun every 365 days, or year. Every 4 years we need to have a leap year with an extra day to make up the difference between the calendar year (365 days) and the time it takes for one complete orbit of the Sun. The year is divided into 12 months, which roughly correspond with the time it takes for the Moon to complete one full orbit of the Earth.
Picture credit: google
Sundials are the simplest way to measure time during the day. A simple stick casts a shadow that grows shorter until midday, when the Sun is at its highest in the sky. The shadow grows longer again after midday. A sundial simply casts its shadow onto a plate marked with the hours. Sundials have been used for many centuries, and are still in use today.
Picture credit: google
People have always organized their lives by the passing of time. The earliest hunters had to hunt during the hours of daylight. When farming had developed, it was important for farmers to understand the seasons in order to plant their crops at the right time.
Long ago, people realized that the movement of the Sun allowed them to recognize the time of day. They also realized that the movement of the Moon was regular and could be used to give measurements of roughly one month. Modern life is governed much more by time, and we now depend on highly accurate clocks to measure every second of the day.
Picture credit: google
For thousands of years people have used levers as a way of transferring a force from one place to another, and to change the amount of movement that results.
To move a heavy object, a long lever can help. The lever is free to move about a point called the fulcrum. The shorter end of the lever is placed under the object, and force is applied to the longer end. This will cause the object to be lifted, but the long end of the lever will have to be pushed down a long way to lift the object only a short distance. With a long-enough lever you could lift a car for a short distance.
Picture credit: google
A gyroscope is a heavy metal wheel made with ball bearings that reduce friction. Once the wheel is set spinning at high speed in an upright position, the force of gravity will try to topple it. However, the effects of gravity are countered by another force called precession. This force means that a spinning body tends to move at right angles to any force that tries to change its direction of rotation. The effect is to keep the gyroscope in the same position until it has slowed down so much that gravity overcomes precession.
Picture credit: google
When you whirl something around your head on the end of a string it flies outwards, and appears to defy the force of gravity. Centrifugal force is acting to pull the object away. The object tries to fly off, and you are applying a force to retain it. This is called centripetal force. The centripetal force stops suddenly when you let go of the string, and centrifugal force makes the object fly away in a straight line. These forces are the reason why you can whirl a bucket of water around above your head without spilling a drop.
Picture credit: google
Due to a force called inertia, an object will remain still or travel in a straight line unless some force interferes with it. Friction is one such force. The greater the mass of an object, the greater its inertia, and the bigger the force that will be needed to start it moving. This is why it is very difficult to move a stationary car by pushing it, but much easier once the car starts to roll. A very strong man is able to pull along a railway carriage once it has started to move. Inertia is the explanation for the magician’s trick of pulling a tablecloth off a table without disturbing the china and cutlery on it.
Picture credit: google
Falling objects are subject to the force of gravity, and as they fall their speed increases, or accelerates, by 9.8 m per second every second. This increase continues until the friction of the air becomes so great that acceleration stops and the object then fall at a constant speed.
Gravity produces the same force on any object, no matter how heavy or light it is. In a vacuum, a feather would fall and accelerate just as quickly as a brick. When a bullet is fired from a gun, the force of the explosion accelerates the bullet along the gun barrel. This force stops immediately the bullet leaves the gun, and friction begins to slow the bullet’s speed.
Picture credit: google