Christine Yarbrough, age 16, of Gary, Ind., for her question:
WHEN WERE WEIGHING SCALES FIRST USED?
One of the scales used today to weigh heavy industrial loads is called the electronic scale. In many cases, it can do a job faster and less expensively than can other kinds of scales. The weight reading indicator can be located up to 2,000 feet away from the scale itself, making it possible to transmit weight readings directly to calculators of computers.
A weighing scale is a device used to measure weight. Some scales are designed to weigh a few grains of chemicals while others can easily weigh railroad boxcars.
There are four main types of weighing scales: balances, spring scales, mechanical scales and electronic scales.
Oldest of all weighing scales are balances. These were used in ancient Egypt about 3000 B.C. They were probably developed from the shoulder yoke, a device that balanced two loads to make them easier to carry.
There are two main types of balances: the equal arm balance and the steelyard.
The equal arm balance is made up of a horizontal beam with a pan suspended from each end. The beam is supported at its center by a thin edge of metal. The object being weighed is put in one pan while weights of known quantity are placed in the other pan until the two balance.
The steelyard was developed about 2,000 years ago in ancient Rome. This scale uses a small weight to balance a heavy load. The beam of a steelyard has arms of unequal lengths. A pan on the shorter arm holds the object being weighed and the load is balanced by moving a weight along the longer arm. Doctors still use a type of steelyard to weigh patients.
Spring scales were invented about A.D. 1700 and are made up of a pan or platform that hangs or rests on a spring. The object being weighed stretches the spring and moves a pointer.
The mechanical scale was developed in the late 1900s and uses a series of levers to balance a load against a known weight. The load is put on a platform that is supported by two or more connected levers. The levers divide the load so that a small weight can be used to balance a heavy load. A dial attached to the scale indicates the weight of the load.
Electronic scales were introduced during the mid 1900s. They use various electrical methods to measure and indicate weight. Most have a device called a strain gage load cell which measures the amount of pressure caused by the weight of the load on the scale.
Large mechanical scales are used to weigh trucks and railroad cars. Supermarkets use smaller mechanical scales to weigh food products.
Industries also use electronic scales to weigh trucks and other heavy equipment. Electronic equipment is also used extensively in many markets to weigh meat and other items.