Erin Wheeler, age 15, of Camden, N.J., for her question:
WHEN WAS THE FIRST WEIGHING SCALE USED?
The oldest types of scales were balances and they were used in ancient Egypt about 3000 B.C. Ancient balancing scales probably developed from the shoulder yoke, a device that balanced two loads to make them easier to carry. The two main kinds of balances are the equal arm balance and the steelyard.
The simple equal arm balance is made of a horizontal beam with a pan suspended from each end. The beam is supported at its center by a thin edge of metal or some other hard substance. The object being weighed is placed in one pan and weights of known quantity are placed in the other pan until the two pans balance. Most balances have a pointer to indicate balanced pans.
The steelyard was developed by the ancient Romans about 2,000 years ago. This kind of scale uses a small weight to balance a heavy load. The beam of a steelyard has arms of unequal length. A pan on the shorter arm holds the object being weighed. The load is balanced by moving a weight along the longer arm. Markings on this arm indicate the weight of the load.
Spring scales were invented about A.D. 1700. They consist of a pan or platform that hangs from or rests on a spring. The weight of the object being weighed stretches or compresses the spring. This action moves a pointer on a dial and shows the weight of the load.
Mechanical scales, developed in the late 1800s, use a system of levers to balance a load against a known weight. The load is placed on a platform that is supported by two or more connecting levers. The levers divide the load so that a small weight can be used to balance a heavy load. Mechanical scales can be used to measure extremely heavy loads.
Electronic scales were introduced during the mid 1900s. They use various electrical methods to measure and indicate weight.
Most electronic scales have a device called a strain gauge load cell. This device measures the amount of pressure caused by the weight of the load placed on the scale. It converts the measurements into an electrical signal and transmits the signal to a weight indicator.
The weight indicator converts the signal into a weight reading.
Electronic scales can weigh some heavy loads faster and less expensively than can other kinds of scales. The weight reading indicator of an electronic scale can be placed up to 2,000 feet away from the scale itself.
Many electronic scales can transmit weight readings directly to adding machines, calculators and computers.
Industries use electronic scales to weigh trucks, railroad cars and other heavy equipment. Supermarkets use these scales to weigh meat, produce and other items.